Vulnerability Assessment of Buried Pipelines - IIIT Hyderabad

Vulnerability Assessment of Buried Pipelines by Pradeep Kumar Ramancharla, Terala Srikanth, Vasudeo Chaudhary, Chenna Rajaram, Bal Krishna Rastogi, Santhosh Kumar Sundriyal, Ajay Pratap Singh, Kapil Mohan

Report No: IIIT/TR/2014/-1

Centre for Earthquake Engineering International Institute of Information Technology Hyderabad - 500 032, INDIA March 2014

VACI/IIIT-H/Report: 04

Assessment of Vulnerability of Installation near Gujarat Coast Vis-à-vis Seismic Disturbances Title: Draft Report on Vulnerability Assessment of Buried Pipelines

International Institute of Information Technology Hyderabad

Institute of Seismological Research Government of Gujarat, India

Ministry of Earth Sciences Government of India August 2013

Earthquake Engineering Research Centre International Institute of Information Technology Gachibowli, Hyderabad – 500 032, India

Vulnerability Assessment of Buried Pipelines

Participants

From International Institute of Information Technology, Hyderabad Ramancharla Pradeep Kumar Terala Srikanth Vasudeo Chaudhary Chenna Rajaram

From Institute of Seismological Research, Govt. of Gujarat Bal Rastogi Santosh Kumar Sandriyal Ajay Pratap Singh Kapil Mohan

2



3


Abstract Pipelines have been acknowledged as the most reliable, economic and efficient means for the transportation of water and other commercial fluids such as oil and gas. They are often referred to as “lifelines”, since they carry materials essential to the support of life and maintenance of property. The earthquake safety of buried pipelines has attracted a great deal of attention in recent years. Many buried pipelines in India run through high seismic areas and therefore are exposed to considerable seismic risk. Pipelines running through high seismic zones should be designed in such a way that they remain functional even after subjected to high intensity earthquake shaking. In this report, performance of one of the high pressure gas pipeline in the state of Gujarat, under the fault movement and soil liquefaction is carried out. Based on the result from the study some recommendations are made to minimize the effect of earthquake on the existing pipeline. In the design of a pipeline for crossing a fault line, the following considerations generally will improve the capability of the pipeline to withstand differential movement. The following recommendations are as follows: 1. The pipelines crossing fault line should be oriented in such a way to avoid compression in the pipeline. Abrupt changes in wall thickness should be avoided within fault zone. In all areas of potential ground rupture, pipelines should be laid in relatively straight section avoiding sharp changes in direction and elevation. 2. To the extent possible, pipelines should be constructed without field bends, elbows, and flanges that tend to anchor the pipeline to the ground. If longer length of pipeline is available to conform to fault movement, level of strain gets reduced. Hence, the points of anchorage should be provided away from the fault zone to the extent possible in order to lower the level of strain in the pipeline. 3. The burial depth of pipeline should be minimized within fault zones in order to reduce soil restrain on the pipeline during fault movement. Pipelines may be placed on the above ground sliding supports. 4. In the design of a pipeline for in the Liquefied zone, the following considerations generally will improve the capability of the pipeline to withstand buoyancy force due to soil liquefaction. The buoyancy effect can also be minimized by shallow burial of the pipeline above the ground water level. An increase in pipe wall thickness will increase the pipeline’s capacity for buoyancy force due to soil liquefaction.

4


Table of Contents 1. Introduction………………………………………...……………………………….….……1 2. Pipeline Scenario in India……………………………………………………….…….……3 2.1

Petroleum pipeline………………………………………………………….…...3

2.2

Gas pipeline……………………………………………………………………...3

2.3

Crude oil pipeline……………………………………………………………….4

3. Pipeline policies and guidelines…………………………………………………….…..…7 3.1

Policy……………………………………………………………………………...7

3.2

Transnational pipelines…………………….……..………………………….…8

3.3

Indian Standards…..……………………………….……………………………8

4. Past pipeline performances…………………………………………………………..…...13 4.1

Seismic Hazard……….……………………………………….……..…………13

4.2

Indian context………………………………………………….……………….13

5. Effects of earthquake on pipelines …….…………………………………………………14 5.1

Continuous pipeline……………………………………………………….......16 5.1.1

Tensile failure………………………………………………………..…16

5.1.2

Local buckling………………………………………………………….16

5.1.3

Beam buckling………………………………………………………….17

5.2

Segmented pipeline…...………………………………………….……………17 5.2.1

Axial Pullout ….……………………………………………………..…17

5.2.2

Crushing of bell and spigot joints…………………………………….19

5.2.3

Flanged joint failure…...……………………………………………….19

5.2.4

Circumferential flexural failure and joint rotation………………….20

6. Vulnerability Assessment of buried pipelines…….....………………………………….21 6.1

Location 1-5………………..……………………………………...…….………21

6.2

Parametric study………………..………………………...……...…….………70

7. Conclusions…...…………………………………………………………………………….81 8. References…………………………………………………………………...……………...83

5


List of figures 1. A map of India’s Oil product pipelines of Gujarat state ...………………………….2 2. India’s product pipelines (Source: Petronet India Ltd)………………...……………5 3. Crude oil and gas pipelines in India ………………………………………………….6 4. Effect of landslide on pipeline resting tensile strain (ASCE, 1984) ……………….16 5. Locally buckling steel gas pipeline in the compression zone at North slope of Terminal Hill in 1994 Northridge earthquake. (EERI, 1995)….....…………………17 6. Beam buckling of a water pipeline made of iron. (USGS Photo Library) ……..…18 7. Axial pull-out at the joint of a water supply pipeline at Tangshan East Water Works in Tangshan Earthquake 1976 (EERL, 2004) ……………………….…….…18 8. Failed cast iron pipe due to failure of bell and spigot joint at Navlakhi port due to lateral spread in 2001 Bhuj earthquake (ASCE, 2001)………………………………………………..……………………………………19 9. Flanged joint pipe failure. (ASCE, 1997) ……………………………………..…..…20 10. Leaking at bell and spigot joint of water supply pipeline due to bending at Shippy Ghat, Port Blair in M9.0 Sumatra earthquake of 2004 (Photo: Suresh R Dash) ………..…………………………………………………………………………..20 11. a) Pipeline crossing parallel to the ground movement. b) Pipeline crossing transverse to the ground movement…………………………………………………24 12. a) Pipeline crossing parallel to the ground movement. b) Pipeline crossing transverse to the ground movement…………………………………………………34 13. a) Pipeline crossing parallel to the ground movement. b) Pipeline crossing transverse to the ground movement…………………………………………………43 14. a) Pipeline crossing parallel to the ground movement. b) Pipeline crossing transverse to the ground movement…………………………………………………53 15. a) Pipeline crossing parallel to the ground movement. b) Pipeline crossing transverse to the ground movement…………………………………………………62 16. Total strain vs pipe thickness for pipe diameter is 12 “……………………………71 17. Total strain vs pipe thickness for pipe diameter is 18 “……………………………72 18. Total strain vs pipe thickness for pipe diameter is 24 “……………………………73 19. Total strain vs pipe thickness for pipe diameter is 30 “……………………………74

6


7


List of Tables 1. Summary of IOC pipelines in the last year ………...………………………..……….5 2. Details of six pipelines by Reliance Industries Ltd ………….………………………6 3. Earthquake impact on Gujarat state during 1901-2002……….……………………11 4. Maximum strains in the pipe in compression and tension in four cases ………...32 5. Maximum strains in the pipe in compression and tension in four cases …...……41 6. Maximum strains in the pipe in compression and tension in four cases.………...50 7. Maximum strains in the pipe in compression and tension in four cases ...………60 8. Maximum strains in the pipe in compression and tension in four cases...………69 9. Strains due to internal pressure and temperature change with pipe wall thickness for pipe diameter is 12” ………...……………………….……………………..…...…70 10. Strains due to internal pressure and temperature change with pipe wall thickness for pipe diameter is 18” ………...……………………….……………………..…...…71 11. Strains due to internal pressure and temperature change with pipe wall thickness for pipe diameter is 24” ………...……………………….……………………..…...…72 12. Strains due to internal pressure and temperature change with pipe wall thickness for pipe diameter is 30” ………...……………………….……………………..…...…73 13. Longitudinal strains in the pipe due to tension and compression for pipe diameter is 12” ………...……………………...………….……………………..…...…74 14. Longitudinal strains in the pipe due to tension and compression for pipe diameter is 18” ………...……………………...………….……………………..…...…75 15. Longitudinal strains in the pipe due to tension and compression for pipe diameter is 24” ………...……………………...………….……………………..…...…75 16. Longitudinal strains in the pipe due to tension and compression for pipe diameter is 30” ………...……………………...………….……………………..…...…76 17. Total strains in the pipe due to tension Pipe diameter is 12” and fault displacement 1.5m………...……………………………..……………………..…...…76 18. Total strains in the pipe due to tension Pipe diameter is 18” and fault displacement 1.5m………...……………………………..……………………..…...…76 19. Total strains in the pipe due to tension Pipe diameter is 24” and fault displacement 1.5m………...……………………………..……………………..…...…77

8

Vulnerability Assessment of Buried Pipelines 20. Total strains in the pipe due to tension Pipe diameter is 30” and fault displacement 1.5m………...……………………………..……………………..…...…77 21. Total strains in the pipe due to tension Pipe diameter is 12” and fault displacement 2.5m………...……………………………..……………………..…...…78 22. Total strains in the pipe due to tension Pipe diameter is 18” and fault displacement 2.5m………...……………………………..……………………..…...…78 23. Total strains in the pipe due to tension Pipe diameter is 24” and fault displacement 2.5m………...……………………………..……………………..…...…78 24. Total strains in the pipe due to tension Pipe diameter is 30” and fault displacement 2.5m………...……………………………..……………………..…...…79 25. Total strains in the pipe due to tension Pipe diameter is 12” and PGA =0.45g …79 26. Total strains in the pipe due to tension Pipe diameter is 18” and PGA =0.45g …79 27. Total strains in the pipe due to tension Pipe diameter is 24” and PGA =0.45g …80 28. Total strains in the pipe due to tension Pipe diameter is 30” and PGA =0.45g …80

9


1. Introduction Pipelines have been acknowledged as the most reliable, economic and efficient means for the transportation of water and other commercial fluids such as oil and gas. These pipeline systems are commonly used to transport water, sewage, oil, natural gas and other materials. They are often referred to as “lifelines” since they carry materials essential to the support of life and maintenance of property. The earthquake safety of buried pipelines has attracted a great deal of attention in recent years. Pipelines are important lifeline facilities spread over large area and encounter a range of seismic hazards and soil conditions. Many buried pipelines in India run through high seismic areas and therefore are exposed to considerable seismic risk. Pipelines running through high seismic zones should be designed in such a way that they remain functional even after subjected to high intensity earthquake shaking. Pipeline systems are commonly used to transport water, sewage, oil, natural gas, etc over a large area and encounter a variety of seismic hazards and soil conditions. Pipelines are generally buried below ground primarily for aesthetic, safety, economic and environmental reasons. The gas and liquid fuel pipelines are generally welded at the joints to act as a continuous pipeline. Pipelines having rigid joints (i.e., strength and stiffness of joints are more than that of pipe barrel) are generally referred to as continuous pipelines (e.g., steel pipe with welded connection). On the other hand, the water supply pipelines with mechanical joints are generally treated as segmented pipelines. These segmented pipelines consist of pipe segments that are connected by relatively flexible connections (e.g., cast iron with bell and spigot joint). Modern pipelines manufactured with ductile steel with full penetration butt welds at joints possess good ductility. It has been observed that the overall performance record of oil and gas pipeline systems in past earthquakes was relatively good. However catastrophic failures did occurs in many cases, particularly in areas of unstable soils. Failures have mostly been caused by large permanent soil displacements (FEMA-233). A pipeline transmission system is a linear system which traverses a large geographical area, and soil conditions thus, is susceptible to a wide variety of seismic hazards. Ruptures or severe distortions of the pipeline are most often associated with relative motion arising from fault movements, landslides, liquefaction, loss of support, or differential motion at abrupt interfaces between rock and soil. Notable the most catastrophic damages are the once resulting from faulting and liquefaction. India is currently making huge investments in pipelines. Considering high seismicity of our country, it is important to ensure seismic safety of buried pipelines. Gujarat is one of the high earthquake prone states in India. And in last few years many state owned

10

Vulnerability Assessment of Buried Pipelines and private organizations had build up their pipeline networks across the state. Owing to these facts the performance of buried and above ground pipeline structures subjected to faulting and soil liquefaction effect and other seismic hazards have become an important subject of study. Gujarat State Petronet Ltd organization intends to expands its grid to 2200kms with an outreach to all the 25 districts of Gujarat thereby enabling industry, households and transportation to drive the benefits of an environment friendly fuel.

Figure 1. A map of India’s Oil product pipelines of Gujarat state This report illustrates the performance of one of the high pressure gas pipeline in the state of Gujarat, under the fault movement and soil liquefaction. Based on the result from the study some recommendations are made to minimize the effect of earthquake on the existing pipeline. Important characteristics of buried pipelines are that they generally cover large areas and are subject to a variety of geotectonic hazards. They can be damaged either by permanent movements of ground (i.e., PGD) or by transient seismic wave propagation. Permanent ground movements include surface faulting, lateral spreading due to liquefaction, and land sliding. Although PGD hazards are usually limited to small

11

Vulnerability Assessment of Buried Pipelines regions within the pipeline network, their potential for damage is very high. On the other hand, wave propagation hazards typically affect the whole pipeline network, but the rate of damage is lower (i.e., lower pipe breaks and leaks per unit length of pipe).

2. Pipeline Scenario in India 2.1 Petroleum and gas pipelines in India In view of the strategic importance of the oil & gas industry and oil security, and recognizing the increasing demand for energy, to fuel economic growth, the Government of India (GOI) has developed the ‘India Hydrocarbon Vision 2025’for the oil & gas industry. This vision statement creates a road map that guides the Indian policy on oil & gas up to the period 2025, forms the backbone and lays the framework for the policy initiated for the hydrocarbon sector; comprising the different segments including pipelines (both national and transnational) in a structured and organized manner. Details below present, in brief, the current status of the pipelines systems in India - for crude oil, products pipelines and gas. Pipelines occupy a key position in any petroleum and gas sector’s logistics. Both public sector units and private sector players tried to ensure control over this safe and economical mode of transportation in India. Initially each of these players had plans of laying their own pipelines, but the GOI wanted to ensure systematic growth, thus leading to the creation of Petronet India Ltd (PIL), a financial holding company, in 1998, with the objective of constructing a refined petroleum product pipeline infrastructure in the country. PIL is a joint venture organization of India’s state owned refineries, financial institutions and private sector players on a ‘common career’ basis. It is presently building pipelines that are expected to add 500,000 b/d to India’s current 325,000 b/d of pipe-line capacity for the transportation of refined petroleum products. Presently, a total of eight pipeline projects are being handled by PIL some of which are already in operation while some others are either under execution or in the planning stage. India transports just over 45%of its petroleum products via pipe-lines. A map of India’s Oil product pipelines is shown in Figure 1.

2.2

Gas pipelines

The Gas Authority of India Ltd (GAIL) – now called GAIL India Ltd– a leading public sector enterprise, is the largest gas transmission and marketing company in India. Today GAIL owns over 4000km of pipeline and has about 95%market share in the Natural Gas business in India. Also, more than half of the total urea production in India is gas-based, out of which GAIL contributes more than 90%,thus making a significant contribution to India’s agricultural sector also. The company also completed the world’s longest (1200 km) and India’s first cross country LPG pipe-line from Jamnagar to Loni, near Delhi. There exists a total of 3331km of LPG pipelines in the country, with a

12

Vulnerability Assessment of Buried Pipelines throughput capacity of 8304MMtpa, work on some of which is still in progress. GAIL is now in the process of doubling the throughput capacity of its main Hazira–BijaipurJagdishpur(HBJ) pipeline. Work on the capacity expansion began in 2002 and will eventually raise the capacity of the pipeline from about 1.1 Bcf/d to2.1 Bcf/d. GAIL also plans a new distribution network in West Bengal and a pipeline which could connect Kolkata with Chennai. India is investing heavily in the infrastructure required to support in-creased use of Natural Gas. This has become even more so with the major development in December 2002when Reliance announced its discovery of large volumes of Natural Gas in the Krishna-Godavari basin, offshore from Andhra Pradesh, around India’s Southeast coast. New reserves from this find are estimated at about 5 Tcf. Cairn Energy also reported finds in late 2002 offshore Andhra Pradesh as well as Gujarat, which contains reserves estimated at nearly 2 Tcf. State owned ONGC, which was originally engaged in the gas production from the Bombay-High offshore fields, has further added to gas discoveries on India’s East coast as well. Shell has signed a Memorandum of Understanding with the State Government of Uttar Pradesh in Northern India for the development of a Natural Gas distribution infrastructure. In addition, there are regional gas grids of varying sizes in Gujarat (Cambay Basin),Andhra Pradesh (Krishna-Godavari Basin), Assam(Assam-Arakan Basin), Maharashtra (Ex-Uran Ter-minal), Rajashthan (JaisalmerBasin), Tamilnadu (CauveryBasin), and Tripura (ArakanBasin).

Meanwhile, GSPL(Gujarat State Petronet Ltd)is implementing a 1600 km long gas grid in the state of Gujarat. GSPL was incorporated as a special purpose vehicle by the Gujarat State Petroleum Corporation in December 1998, especially to implement the gas grid for the trans-mission of LNG from import terminals to demand centres across the state.

2.3

Crude oil & petroleum product pipelines

Indian Oil Corporation Ltd.(IOCL) operates the largest net-work of crude and product pipelines and transports petroleum products to the various major demand centres of this geographically vast country and feed four major inland re-fineries. The pipeline division of IOCL has in-house capabilities of executing pipeline projects from concept to commissioning without any external support, whatsoever. Proven project techniques and tools are used in project management to ensure a high level of quality, productivity, time scheduling and cost control. A summary of IOC pipelines, as existed at the end of last year is given below:

13


Table 1. Summary of IOC pipelines in the last year

Figure 2. India’s product pipelines (Source: Petronet India Ltd) Oil India Ltd. transports all crude oil produced in North-East India to refineries via a 1,157 km pipeline. The Oil& Natural Gas Corporation (ONGC),India’s single largest crude producer, has a 7900 km onshore pipeline net-work while its offshore activities include a 3500 km pipeline network. Bharat Petroleum Corporation Ltd(BPCL) and Hindustan Petroleum Corporation Ltd (HPCL) also have product(over 250 km) and crude and product pipelines (over 750 km) respectively in operation as well, in addition to having partnerships with PIL in this economic mode of transport. The CIPL (Central India Pipeline Project), originally intended to be executed by PIL, has now been approved for award by the PIL Board to the joint venture of IOCL and Reliance Industries Ltd (RIL) – previously called Reliance Petroleum Ltd (RPL) -on a build–own– transfer–operate basis. In their proposal for CIPL, IOC and RPL have estimated a cost of

14

Vulnerability Assessment of Buried Pipelines about US$0.32 billion by stripping the spur lines, planned for Bhopal, Indore and Chittorgarh. Under the policy for the development of petroleum product pipelines ‘Common User Principle’, six pipe-lines to be put up by RIL have been approved. These include: Table 2. Details of six pipelines by Reliance Industries Ltd

Pipelines between refineries and major urban centres are replacing rail as the main mode of transportation. Some of the other pipeline projects for crudes and products under consideration/ implementation are: • Vadinar- Bina (crude) • Mundra-Bhatinda (crude) • Bina –Kanpur • Paradip-Rourkela • Bhatinda-Pathankot

15


Figure 3. Crude oil and gas pipelines in India

3. Pipeline Policies and Guidelines 3.1 Policy On September 29, 2003 the GoI announced the draft pipeline gas policy which envisaged the laying of 7,000 km of pipeline network for gas transportation at a cost of around MMUS$ 3902.86 in the next 5-6 years. As a part of this policy, GOI proposes a National Gas Grid on the pattern of the National Power Grid to manage the distribution effectively. While individuals will be permitted to lay pipelines for distribution purposes, say up to 100 km, but if the length is beyond the prescribed limit the construction would be carried out in accordance with the ‘Common Carrier Principle’ to avoid duplication and wasteful expenditure. The main objective of the draft policy, presently undergoing finalization with the GOI, is to put in place a distribution system for carrying gas, the availability of which is likely to improve considerably, it having been struck at several places, as mentioned above, with arrangements for the movement of liquefied Natural Gas (LNG) having been tied up indefinitely. Under the proposed policy, all trunk pipelines covering more than one state or operating at a pressure more than the notified level will be build or managed by a company to be decided by the GOI but, until it is notified, by GAIL India Ltd. Seizing the opportunity, GAIL has un-veiled a MM US$ 4336.51 plan to build a 7,890 km gas grid as shown in Figure 2, along with a completion schedule. The rationale: gas grids in several countries like Italy, France, Turkey and also in China and Korea have been built by the NOCs, because of issues of safety and security. The policy envisages appointment of a Regulator under the Petroleum Regulatory Board Bill 2002 for regulating transmission, distribution, supply and storage systems for Natural Gas/LNG and to promote development of the sector. The Regulator will ensure access to gas pipelines on non-discriminatory common carrier principle for all users. And the tariff for the transmission pipelines and distribution pipelines would be approved by the Regulator. Pipelines in India have traditionally operated at 100%capacity (since these are captive pipelines of oil companies). However, where pipelines are operated under a common carrier principle as mooted in the draft pipe-line policy, they may in reality be faced with uncertainty in utilization, arising from demand supply dynamics. Since these are long life projects, high capacity utilization over long periods becomes a pre-requisite for financial viability. Probably the key issue that requires resolution is the demand by the financial institutions that the proposed pipe-line projects enter into long term ‘Takeor Pay’ contracts. According to some, this demand would largely violate the common carrier principle, which at-tempts to ensure equitable access to all users. The key concern is price.

16

Vulnerability Assessment of Buried Pipelines The principles governing the tariff structure should ensure adequate competition among various mode combinations, fair return to investors (i.e., returns commensurate with the risks assumed), equitable access to all users and equitable costs to consumers. While it is easy to enunciate the broad principles, implementing this could be an extremely complex task, given the peculiarities of the situation and the relative lack of time available for formulation of policy and implementation.

3.2 Transnational pipeline In addition to the pipeline projects being developed within the country as mentioned above, the GOI is trying to strike alliances to import piped gas from gas-rich countries in the vicinity, such as Iran and Turkmenistan in central Asia, Qatar and Oman in West Asia and neighbouring Bangladesh. Proposals for gas pipelines from Iran and Bangladesh are under active consideration. The first proposition is to connect Iran’s South Pars field with the HBJ pipeline. The second preposition is to connect Bangladesh’s Bibiyana gas field in North Eastern Bangladesh with India’s Northern Gas markets. Unocal Corporation and its subsidiaries in Bangladesh have submitted a gas export pipeline proposal, known as The Bangladesh Natural Gas Pipeline Project, and the proposal is pending approval from the Bangladesh Parliament. The recent large gas discovery in Myanmar (OVL and GAIL collectively hold a 30% stake) has opened up a new avenue for importing gas into India. The emergence of this option would have a significant impact on the business dynamics of the proposed transnational pipelines from Iran and Bangladesh. Another crucial factor in this segment should be the progress made by the GOI in its efforts to improve the Geopolitical scenario in the region. GOI’s pricing policy (under formulation) would play a crucial role in the demand supply scenario of gas, as the user industries have alter-native options to gas. Once GOI clarifies its stand on gas pricing, LNG policy and the common carrier principle, significant, positive implications for the commercial aspects of the natural gas industry in India should be forthcoming.

3.3 Indian Standards The following codes and reports have been used in the preparation of this report. 1. IS 15663(Part 1):2006 This code covers requirements and recommendations for the design, materials, construction and testing of pipelines made of steel and used in the transportation of natural gas and re-gasified liquid natural gas (RLING). 2. IS 15663(Part 2):2006 The code covers the minimum requirements for design, installation and testing of pipelines of steel, crossing roads, railways, water courses and other buried services. 3. IS 15663(Part 3):2006 This code covers requirements for pre-commissioning and commissioning of pipelines.

17

Vulnerability Assessment of Buried Pipelines 4. IS 15654:2006 The standard provides guidelines for the definition, specification, performance analysis, and application of systems used for supervisory control and data acquisition for oil and gas pipe lines. 5. IS 15655:2006 This standard enlists various types of telecommunication facilities required for smooth and efficient operation and maintenance of oil and gas pipelines. 6. IS 15667:2006 This standard applies to data-acquisition and trend-monitoring systems for gas turbine installations and associated systems. 7. IS 15664:2006 This standard specifies procedures and rules for the conduct and reporting of acceptance tests in order to determine and/or verify the power, thermal efficiency and other performance characteristics of gas turbine power plants. 8. IS 15666(Part 1):2006 This standard covers terms and definitions relevant to the procurement of gas turbine systems. 9. IS 15666(Part 2):2006 This standard specifies the standard reference conditions and standard ratings for gas turbines. 10. IS 15666(Part 3):2006 This standard covers the design requirements for the procurement of all applications of gas turbines and gas turbine systems, including gas turbines for combined cycle systems and their auxiliaries, by a purchaser from a packager. It also provides assistance and technical information to be used in the procurement. 11. IS 15666(Part 4):2006 This standard provides guidelines for procurement of gas turbines with consideration of the fuel quality and of the environmental performance. Guidance is given to both the packager and purchaser on what information should be provided with regard to the fuel used by a gas turbine, and with regard to the type of information necessary to quantify the expected environmental impact. 12. IS 15666(Part 5):2006 This standard specifies requirements and gives recommendations for the design, materials, fabrication, inspection, testing and preparation for shipment of packaged gas turbines for use in drilling, production, refining and the transport by pipelines of petroleum and natural gas. It is applicable to the procurement of gas turbines and gas turbine systems, including gas turbines for combined cycle systems, and their auxiliaries by a purchaser from a packager. 13. IS 15666(Part 7):2006 This standard specifies the information that needs to be submitted during the proposal and contract stages of a project for the entire scope of supply for which the packager will assume technical and contractual responsibility. 14. IS 15666(Part 8):2006 This standard states the principles for systems and procedures to assure the integrity of a packager’s product and services. It gives guidance on the inspection, testing, installation and commissioning required for the package and

18

Vulnerability Assessment of Buried Pipelines packaged equipment. It outlines the responsibilities between the purchaser and packager for inspection, coordination, reporting and recording. 15. IS 15666(Part 9):2006 This standard provides a basis for exchange of information about reliability, availability, maintainability and safety between gas turbine manufacturers, users, consultants, regulatory bodies, insurance companies and others. It also describes component life expectancy, repairs and criteria for determining overhaul intervals. 16. IS 15665:2006 This standard gives terms and definitions used in the field of gas turbines and applies to open-cycle gas turbines, closed-cycle, semiclosed-cycle and combined-cycle gas turbines. 17. IS 15657:2006 This standard specifies requirements for centrifugal pumps, including pumps running in reverse as hydraulic power recovery turbines, for use in petroleum, petrochemical and gas industry process services. 18. IS 15661:2006 This standard specifies requirements and gives recommendations for the design, materials, fabrication, inspection, testing and preparation for shipment of centrifugal compressors for use in the petroleum, chemical and gas service industries. 19. IS 15659(Part 1):2006 This standard specifies requirements of plant applied external three layer extruded polyethylene and polypropylene based coatings for corrosion protection of welded and seamless steel pipes for pipeline transportation of gas and liquid hydrocarbons in the petroleum and natural gas industries. 20. IS 15659(Part 2):2006 This standard specifies the requirements for qualification, application, testing and handing of materials for plant application of single layer Fusion Bonded Epoxy (FBE) coatings applied externally for the corrosion protection of bare steel for use in pipeline transportation systems for the petroleum and natural gas industries. 21. IS 8062:2006 This code deals with general principles and requirements for cathodic protection system for prevention against corrosion of external underground buried surface of metallic high pressure hydrocarbon product pipeline/structure. This standard is intended to serve as a guide for establishing minimum requirements for control of external corrosion on pipeline/structure system. 22. IS 15678:2006 This code provides a uniform authentic reference to the pipeline operators which shall help them in taking decisions about selection of appropriate Magnetic Flex Leakage (MFL) tool for inline inspection to assess the health of the pipeline segment in quantifiable terms besides keeping them fully aware as to what best can be expected out of intelligent pigging inspection. 23. IS 15679:2006 This code covers the minimum requirements of materials, equipments and accessories for hot tapping and stopple plugging/line plugging operations of

19

Vulnerability Assessment of Buried Pipelines onshore natural gas pipelines. It covers the minimum safety requirements to be maintained during welding, cutting and plug setting, etc, while carrying out the hot tapping and stopple plugging/line plugging operations on pipelines. 24. IS 15672:2006 This standard provides guidance on selection, installation, calibration, performance and operation of Corioils meters for the determination of mass flow, density, volume flow and other related parameters of fluids, synonymous for liquids and gases. 25. IS 15673:2006 This standard specifies the requirements for the construction, methods of pressure tapping, working ranges with normal values of minimum/maximum flow rates and permissible errors for rotary piston meters. 26. IS 15674:2006 This standard covers multipath ultrasonic transit-time flow-meters, used for custody transfer measurement of natural gas for gas temperature between -10˚ to 55˚C. 27. IS 15675:2006 This standard specifies the geometry and method of use (installation and operating conditions) of orifice plates when they are inserted in a conduit running full to determine the flow rate of the fluid flowing in the conduit. 28. IS 15676:2006 This standard specifies the requirements of dimensions, ranges, construction, performance, calibration and output characteristics of turbine meters for gas flow measurement for custody transfer. It also specifies installation conditions, leakage testing and pressure testing and provides recommendations for use, field checks & perturbations of the fluid flowing. 29. IS 15677:2006 This code gives guidance on the specification, design, installation, operation and maintenance of metering systems for high accuracy flow measurement, estimation of uncertainty, secondary instrumentation, gas properties related to metering of natural gas and related safety aspects. These guidelines cover five types of meters namely orifice, turbine, ultrasonic, rotary and coriolis. 30. IS 15729:2007 This code covers the commissioning, operation and maintenance and safety aspects of natural gas pressure regulating and metering terminal. The table below shows the locations of the different earthquakes that have occurred in the past. Table 3. Earthquake impact on Gujarat state during 1901-2002 Date

Magnitude (Richter)

Intensity (MSK) & Location

Impact

Source

16 June

Mw 7.5

X 23.60N,

About 3,200 people were killed and

Bilham, ‘99

20

Vulnerability Assessment of Buried Pipelines 1819

69.60E

13 August 1821

5

19 August 1845

6

VII 23.80N, South-east of lakhpat kutchh District 68.90E affected.

26 April 1848

6

VII 24.40N, Damage in the Mount Abu area. 72.70E

29 April 1864

5

VII 22.30N, Surat-Ahmedabad area affected. 72.80E

14 January 1903

6

24.00N, 70.00E

North-east affected.

21 April 1919

5.5

VIII 22.00N, 72.00E

Bhavnagar District affected.

14 July 1938

5

VI 22.40N, 71.80E

23 July 1938

5.5

31 October 1940

Ms 5.8

21 July 1956

6.1

V 22.70N, 72.70E

dozens of towns and villages were destroyed in kutchh and adjoining parts of southern Pakistan. The earthquake resulted in great surface deformation including a 90-kilometer stretch that was uplifted about 4m, called the Allah Bund. The shock was felt throughout South Asia as far as Kolkata. Kaira-Daman-Ahmedabad affected.

of

kachchh

District

Morbid

USGS & NEIC USGS & ASC USGS & ASC USGS & ASC USGS & ASC USGS & ASC

Paliyad region in Bhavnagar District affected.

VII 22.40N, Felt at Rajkot, 71.80E Vikramgad. 23.70N, 69.10E

area

and

USGS & ASC USGS & ASC

Kutchh District affected.

ASC

115 people killed and hundreds injured. 1,350 buildings destroyed at Anjar alone. Felt over an area with a radius of 330 Km and as far as

GSI

21

Vulnerability Assessment of Buried Pipelines Mumbai and Hyderabad (Pakistan).

23 March 1970

Ms 5.4

26 people killed and 200 people injured in Bharuch and the neighbouring villages. Heavy damage in Bharuch city. Ground fissures reported over a distance of 20Km and large amounts of water and sand emitted from them. The quake was also felt in Ankleshwar, Bhavnagar, Surat and Vadodara cities.

ANSS & ASC

4. Past Pipeline Performances 4.1 Seismic Hazard A pipeline transmission system being a linear system which traverses a large geographical area, and soil conditions thus, is susceptible to a wide variety of seismic hazards. The major seismic hazards which significantly affect a pipeline system are: i) ground failure, ii) ground motion and iii) others miscellaneous effects. While ground failure includes faulting, liquefaction and earthquake induced landslides, tsunamis, and other affect of supporting and surrounding structures are usually placed under miscellaneous hazards. Ruptures or severe distortions of the pipeline are most often associated with relative motion arising from fault movements, landslides, liquefaction, loss of support, or differential motion at abrupt interfaces between rock and soil. Notably the most catastrophic damages are the ones resulting from faulting or ground rupture. Owing to these facts the performance of buried and aboveground pipeline structures subjected to faulting and other seismic hazards have become important subject of study.

4.2 Indian Context Currently, India has 7,000 km of pipelines. The oil and gas pipeline infrastructure is being accorded top priority by the nation's planners and a network of these pipelines criss-crossing the nation has been planned. The pipeline market itself is estimated to be around US$ 9 Billion over a period of five-six years. The National Gas Grid being implemented by GAIL (India) Ltd, which is expected to take three-four years to reach completion, will lay a 17,000 km pipeline network. The proposed oil pipeline network, on the other hand, is expected to build a pipeline network spanning over more then

22

Vulnerability Assessment of Buried Pipelines 5,000 km. These projects will give an enormous boost to the pipeline demand in the country. Notably, India has had more than five moderate earthquakes (Richter Magnitudes ~6.07.5) since 1988. As noted in IS 1893 Himalayan-Nagalushai region, Indo-Gangetic Plain, Western India, Kutch and Kathiawar regions are geologically unstable parts of the country, and some devastating earthquakes of the world have occurred there. A major part of the peninsular India has also been visited by strong earthquakes. From the past seismic performance of pipelines in various other countries it can be noted that the consequences of pipeline failure due to earthquakes could be an exaggerated one, particularly so for India, both in terms of economic and social aspects. Thus implementing the seismic design considerations at the current phase of Indian pipeline scenario is absolutely essential.

5. Effects of earthquake on pipelines The failure of pipelines during past earthquakes is described below. a) 1971 San Fernando Earthquake: It resulted in direct losses to the pipeline systems by damaging a 1.24 m diameter water pipeline at nine bend and welded joints. Ductile steel pipelines were able to withstand ground shaking but could not withstand ground deformation associated with faulting and lateral spread. Eleven transmission pipelines were damaged by liquefaction induced lateral spread and landslides. Eighty breaks occurred to the underground welded steel transmission pipeline located in the upper San Fernando Valley, the most serious in an old oxyacetylene-welded pipeline. Although located in an uplift zone the failure was caused by compressive forces wrinkling the pipes. b) 1983 Coalinga Earthquake: It caused numerous breaks in the natural gas line but fires did not occur since the main valve was closed manually shortly after the earthquake. Several pipeline failures occurred in oil drilling and processing facilities. In general it was noted that most pipe breaks occurred at pipe connections. c) 1987 Whittier Narrows Earthquake: Damages during this earthquake were usually limited to sections that were corroded or anchored at two locations which experienced large lateral relative displacement. Southern California Gas reported 1411 gas leaks were directly caused by the earthquake. Portions of the California State University, Los Angeles were without gas for 12 weeks. Five fires were reported; three of these were attributed to gas leaks. d) 1989 Loma Prieta Earthquake: This Magnitude 7.1 earthquake caused failure of many pipelines. Damage consisted primarily of broken water lines. Broken waterlines

23

Vulnerability Assessment of Buried Pipelines occurred at the Ford plant from liquefaction and excessive soil pressures. At the Port of Oakland located on the east side of the San Francisco Bay on fill all water lines broke and fire lines ruptured eliminating fire fighting protection. e) 1992 Big Bear Earthquakes: Two earthquakes occurred in San Bernadino County, California, a magnitude 7.5 another of magnitude 6.6. These two events were followed by numerous aftershocks. Horizontal fault rupture displacement associated with this event was from 5 to 9.5 feet. Most pipeline damage was associated with the rupture zone. f) 1994 Northridge Earthquake: This event caused about 1,400 pipeline breaks in the San Fernando Valley area. Outside the zone of high liquefaction potential, the dispersed pattern of breaks is attributed to old brittle pipes damaged by ground movement. In the On Balboa Boulevard a 0.5588m pipe suffered two breaks, one in tensile failure and the other in compressive failure. These pipe failures were located in a ground rupture zone perpendicular to the pipeline. Leaking gas ignited at several locations. Some broken water and gas lines were found to have experienced 0.1524 to 0.3048 m of separation in extension. The area experienced widespread ground cracking and differential settlements. A 2.159 m sewage pipe ruptured in the Jensen Filtration. g) 1995 Hyogoken-Nanbu Earthquake: Takarazuka City was also heavily damaged. The damage on the water supply pipelines was serious and 203 pipeline damages were reported. Although Sakasedai district has the area of almost 1km square, 30 pipeline damages (pipe material was DCIP) occurred in the 1995 Hyogoken-nanbu earthquake. Almost 50% of damages were occurred in unliquefied ground. h) 1999 (Mw 7.4) Kocaeli, Turkey Earthquake: Substantial water supply damage occurred in many cities. For example, the entire water distribution system in Adapazari was damaged. One of them, a water pipe made of steel with a diameter of 2.4 m, damaged at Kullar due to right-lateral strike-slip. A butt-welded Thames raw water steel pipeline 2.2 m in diameter crosses the Sapanca Segment of the North Anatolian fault and was damaged at the fault crossing. Damage was observed at three locations where a small surface leak was observed in the pipe at point near the fault crossing; a significant leak occurred at yet another point and a minor leak happened at the bend of pipe. i) 1999, the Chichi Earthquake: In Taiwan many buried water and gas pipelines were damaged at many sites. It was reported that buried gas pipelines underwent bending deformation due to ground displacement at a reverse fault near the Wushi Bridge about 10 km south of Taichung. The bending deformation in a 100A-size pipeline was V shaped, with the pipeline being bent at three points. The deformation of a 200A-size pipeline was Z-shaped, with the pipeline being bent at two points. There have been virtually no cases of substantial deformation comparable to this case in gas pipelines comprised of welded steel pipes.

24

Vulnerability Assessment of Buried Pipelines The main seismic hazards that are responsible for pipeline failure can be described as: i) Seismic wave propagation ii) Abrupt permanent ground displacement (faulting) iii) Permanent ground deformation (PGD) related to soil failures a) Longitudinal PGD b) Transverse PGD c) Landslide iv) Buoyancy due to liquefaction The main failure modes of both continuous and segmented pipelines are summarized in the following.

5.1 Continuous pipeline 5.1.1 Tensile failure Tensile strain in the pipeline can arise due to any of the seismic hazards (e.g., faulting, landslide, liquefaction, and relative ground motion) at pipe supports. Figure below illustrates the effect of landslide on the pipeline resting high tensile strain.

Figure 4. Effect of landslide on pipeline resting tensile strain (ASCE, 1984).

5.1.2 Local buckling Local buckling or wrinkling in pipeline occurs due to local instability of the pipe wall. Once the initiation of local shell wrinkling occurs, all subsequent wave propagation and

25

Vulnerability Assessment of Buried Pipelines geometric distortion caused by ground deformation tend to concentrate at these wrinkles. Thus, the local curvature in pipe wall becomes large and leads to circumferential cracking of the pipe wall and leakage. This is a common failure mode for steel pipes. Figure below illustrates local buckling of a 77 inch welded steel pipe during the 1994 Northridge earthquake.

Figure 5. Locally buckling steel gas pipeline in the compression zone at North slope of Terminal Hill in 1994 Northridge earthquake. (EERI, 1995)

5.1.3 Beam buckling Beam buckling of a pipeline is similar to Euler buckling of a slender column; the pipe undergoes an upward displacement. The relative movement is distributed over a large distance and hence the compressive strains in the pipeline are not too large and the potential for tearing of the pipe wall is less. For this reason, beam buckling of a pipeline for a ground compression zone is considered more desirable than local buckling. Beam buckling generally occurs in pipelines buried at shallow depths of about 3 feet or less. This can also happen during post-earthquake excavations, which are carried out deliberately to relieve compressive strain in the pipes. Figure-4 shows beam buckling of a water pipeline made of iron during the M7.8 San Francisco earthquake in 1906.

5.2 Segmented pipeline 5.2.1 Axial pull-out

26

Vulnerability Assessment of Buried Pipelines In the areas of tensile ground strain the common failure mechanism of a segmented pipeline is axial pull-out at joints, since the shear strength of joint caulking material is much less than that of the pipe. Figure shows a 30cm diameter cast iron pipeline pulled apart 25cm during 1976 Tangshan earthquake.

Figure 6. Beam buckling of a water pipeline made of iron. (USGS Photo Library)

Figure 7. Axial pull-out at the joint of a water supply pipeline at Tangshan East Water Works in Tangshan Earthquake 1976 (EERL, 2004)

27


5.2.2 Crushing of bell-and-spigot joints In areas of compressive strain, crushing of bell-and-spigot joints is a very common failure mechanism. Figure shows the failure of a cast iron pipe due to failure of bell and spigot joint at Navlakhi port area during Bhuj earthquake of January-26, 2001.

Figure 8. Failed cast iron pipe due to failure of bell and spigot joint at Navlakhi port due to lateral spread in 2001 Bhuj earthquake (ASCE, 2001)

5.2.3 Flanged joint failure In the areas of tensile ground strain, flanged joint pipeline may fail at joint due to breaking of the flange connection. Figure shows a flanged joint pipe failure due to higher tensile strain.

28


Figure 9. Flanged joint pipe failure. (ASCE, 1997)

5.2.4 Circumferential flexural failure and joint rotation When a segmented pipeline is subjected to bending induced by lateral permanent ground movement or seismic shaking, the ground curvature is accommodated by some combination of rotation of joints and flexure in the pipe segments. The relative contribution of these two mechanisms depends on the joint rotation and pipe segment flexural stiffness. Figure shows the pipeline leaking at its joint due to excessive bending in 2004 Sumatra earthquake.

Figure 10. Leaking at bell and spigot joint of water supply pipeline due to bending at Shippy Ghat, Port Blair in M9.0 Sumatra earthquake of 2004 (Photo: Suresh R Dash)

29


6. Vulnerability assessment of buried pipelines 6.1 Location 1-5 Today, underground conduits serve in diverse applications such as sewer lines, drain lines, water mains, gas lines, telephone and electrical conduits, culverts, oil lines, coal slurry lines, subway tunnels, and heat distribution lines. Among these seismic design of buried pipeline has great importance in the field of lifeline engineering. The pipelines are usually buried below ground for economic, aesthetic, safety and environmental reasons. In certain circumstances it may be required to take those pipes above ground but this case is relatively uncommon. Generally the oil and gas pipelines are designed and constructed as continuous pipelines, while water supply pipelines are constructed as segmented pipelines. Failures have mostly been caused by large permanent soil displacements. This section discusses seismic analysis method for buried pipes subjected to a strong earthquake. This can be used as a basis for evaluating the level of strengthening or increased redundancy needed by existing facilities to improve their response during seismic events. So this covers design criteria for wave propagation, fault crossing and permanent ground deformation (PGD) due to liquefaction, lateral spreading, etc. This analysis and design criteria require the following engineering information. Pipeline information a) Pipe geometry (diameter, thickness); b) Type of joint; c) Stress-strain relationship of pipe material; d) Pipeline function and its post seismic performance requirement; e) External pipe coating specification; f) Operating pressure in the pipe; g) Operational and installation temperature; h) Pipeline alignment detail (plan, profile location of fittings, etc); and i) Reduced strain limit for existing pipelines. Site information

30

Vulnerability Assessment of Buried Pipelines a) Burial depth of the pipeline; b) Basic soil properties (unit weight, cohesion, internal friction angle and in situ density). c) Properties of backfill soil in the trench; d) Depth of water table; and Seismic hazard information a) Expected amount of seismic ground motion at the site; b) Expected amount and pattern of permanent ground deformation and its spatial extent; c) Length of pipeline exposed to permanent ground deformation; d) Active fault locations; expected magnitude of fault displacement, and orientation of pipeline with respect to direction of fault movement. The seismic safety evaluation of a continuous oil pipeline as follows:

Location 01: The continuous buried pipeline is designed to carry natural gas at a pressure of 9.3MPa. The pipe is of API X-60 grade with 30-in (0.762m) diameter (D) and 0.0064 m wall thickness (t). The installation temperature and operating temperature of the pipeline are 300 C and 650 C respectively. The pipeline is buried at 1.5m of soil cover. Poisson’s ratio and coefficient of thermal expansion of the pipe material can be considered as 0.3 and 12 x 10-6 respectively. This pipeline is checked for four cases they are Case I: Permanent ground displacement (PGD) Case II: Buoyancy due to liquefaction Case III: Fault crossing Case IV: Seismic wave propagation For API X-60 Grade pipe: Yield stress of pipe material = σy = 413 MPa Ramberg-Osgood parameters n = 10 and r =12.

31

Vulnerability Assessment of Buried Pipelines Pipe strain due to internal pressure is calculated as follows The longitudinal stress induced in the pipe due to internal pressure will be Sp =

PDµ 9300000 × 0.762 × 0.3 = 2t 2 × 0.0064

=166.09 x 106 N/m2 = 166.09MPa Using Ramberg-Osgood’s stress-strain relationship the longitudinal strain in the pipe will be εp =

S Sp  1 + n  p E  1 + r  σ y 

   

r

  

 166.1 × 10 6  10  166.1 × 10 6 1 + = 2 × 1011  1 + 12  413 × 10 6 

12 

   

  

= 0.0008305 = 0.08305% (tensile) Pipe strain due to temperature change: The longitudinal stress induced in the pipe due to change in temperature will be ST = Eα (T2 – T1) = 2 x 1011 x 12 x 10-6 (65-30) = 84 MPa Using Ramberg-Osgood’s stress-strain relationship the longitudinal strain in the pipe will be  S n  S t ε t = t 1 + E  1 + r  σ y 

   

r

 84 × 10 6  109 1+ = 11  1 + 12 2 × 10 

  

 84 × 10 6   413 × 10 6 

   

12

   

= 0.00042 = 0.042% (tensile) The total strain in the continuous pipeline due to internal pressure and temperature is

32

Vulnerability Assessment of Buried Pipelines = 0.08305 + 0.042 = 0.125%. Ignoring the strain in pipe due to installation imperfection or initial bending, the above calculated strain can be considered as the operational strain in pipe (i.e., εoper = 0.125%).

Case I: Permanent ground displacement (PGD) The permanent ground deformation refers to the unrecoverable soil displacement due to faulting, landslide, settlement or liquefaction induced lateral spreading.

Figure 11. a) Pipeline crossing parallel to the ground movement. b) Pipeline crossing transverse to the ground movement Here the length and width of PGD zone is 120m and 50m respectively. Soil is sandy soil with an angle of friction (Φ) = 320 and effective unit weight of 18 kN/m3. The ground displacement (δl and δt) due to liquefaction can be taken as 2m. The operational strain in pipeline = 0.125% (tensile) Yield stress of pipe material σy = 413 Ramberg-Osgood parameter (n) = 10 Ramberg-Osgood parameter (r) = 12 Parallel crossing (Longitudinal PGD)

33

Vulnerability Assessment of Buried Pipelines The expected amount of permanent ground movement parallel to pipe axis = δl = 2m The design ground movement = δl design = δl x Ip = 2 x 1.5 = 3m Case-1: The amount of ground movement (δl design) is considered to be large and the pipe strain is controlled by length (L) of permanent ground deformation zone. The peak pipe strain is calculated as  tu L t L  1 + n  εa = u 2π DtE  1 + r  2π Dt σ y 

   

r

   

Where tu = maximum axial soil force per unit length of pipe for soil condition. The maximum axial soil resistance (tu) per unit length of pipe can be calculated as  1+ K 0  1 t u = πDcα + πDH γ  tan δ  2  Where D = diameter of pipe = 0.762m C = Coefficient of cohesion = 30kpa α = Adhesion Factor = 0.608-0.123 x 0.3 – 0.27/(0.33+1) + 0.695 /(0.33 +1) = 0.99645 H = soil cover above the centre of the pipeline = 1.5m Interface angle of friction between soil and pipe δ1 = f Φ Here f = friction factor = 0.7 for smooth steel pipe δ1 = f Φ = 0.7 x 32o = 22.4o K0 = coefficient of soil pressure at rest = 1- sin 32o = 0.47 tu = ̟ x 0.762 x 30000 x 0.99645 + (̟ x 0.762 x 1.5 x 18000 x ((1+0.47)/2)tan22.4o = 91144N/m =91.144kN/m 12  91144 × 120 10  91144 × 120   εa = 1 +     2 × π × 0.762 × 0.0064 × 2 × 10 11  1 + 12  2 × π × 0.762 × 0.0064 × 413 × 10 6   = 0.002023 = 0.2023% Case-2: The length (L) of permanent ground deformation zone is large, and the pipe strain is controlled by the amount of ground movement (δl design). The peak pipe strain for this case is calculated as

34


t L εa = u e 2π DtE

  t L 1 + n  u e  1 + r  2π Dt σ y 

   

r

   

Where Le = Effective length of pipeline over which the friction force (tu) acts, which can be calculated by the following equation. δ ldesign

 t L2  2  n  t u L e = u e 1 +    πDtE   2 + r  1 + r  πDtσ y 

   

r

  

From this effective length of pipeline is calculated as Le = 100m εa = 0.0015095 The design strain in pipe is taken as the least value between the two cases = εseismic = 0.0015095 The operational strain in the pipeline = εoper = 0.00125 The total tensile strain in the pipeline = 0.0015095 + 0.00125 = 0.0027595 Total compression strain = 0.0015095 – 0.00125 = 0.0002595 The limiting strain in tension for permanent ground deformation is = 0.03 The total strain in pipe due to longitudinal strain is less than the allowable strain. Transverse Crossing: The expected amount of transverse permanent ground deformation (δt) = 2m The design transverse ground displacement = δt design = δt x Ip = 2 x 1.5 = 3m. The maximum bending strain in the pipe is calculated as the least value of the following two A.

B.

ε b= ±

π Dδ tdesign

W2 = ±̟ x 0.762 x 3 / 502 = ± 0.00287267

ε b= ±

Pu W2 3π EtD2

Where Pu = maximum resistance of soil in transverse direction. The maximum transverse soil resistance per unit length of pipe is

35

Vulnerability Assessment of Buried Pipelines Pu = N ch cD + N qh γHD

Where Nch = Horizontal bearing capacity factor for clay c d N ch = a + bx + + ≤9 2 (x +1) (x +1)3 Where x = H/D = 1.5/0.762 = 1.968503937 a = 6.752 b = 0.065 c = - 11.063 d = 7.119 Nch =6.752+ (0.065 x 1.96) + (-11.063/(1.96+1)2) + (7.119/(1.96+1)3) = 5.896 Nqh = Horizontal bearing capacity factor for sandy soil Nqh = a + bx +cx2 + dx3 + ex4 Where x = H/D = 1.5/0.762 = 1.968503937 a = 5.465 b = 1.548 c = - 0.1118 d = 5.625 x 10-3 e = -1.2227 x 10-4 Hence, Nqh = 5.465 + (1.548 x 1.96) + (-0.1118 x 1.962) + (5.625 x 10-3 x 1.963) + (-1.2227 x 10-4 x 1.964) = 8.120 Hence Pu =5.896 x 30000 x 0.762+ (8.120 x 18000 x 1.5 x 0.762) = 301869N/m = 301.869kN/m

εb = ±

301869 × 50 2 3 × π × 2 × 10 11 × 0.0064 × 0.762 2

= 0.1077 Hence, the maximum strain induced in the pipeline due to transverse PGD is taken as Εseismic = ± 0.00287267 (tensile/compressive) The operational strain in the pipeline = εoper = 0.0013 Total longitudinal strain in the pipe in tension 0.00287267+0.0013 = 0.004172 Total longitudinal strain in the pipe in compression = 0.00287267-0.0013 = 0.0016

36

Vulnerability Assessment of Buried Pipelines The allowable strain in tension for permanent ground deformation is = 3% = 0.03 The allowable strain in compression for steel pipe is Εcr-c = 0.175t/R = 0.175 x 0.0064/0.381 = 0.00293 The total strain in pipe due to transverse PGD is less than the allowable strain for both tension and compression. Case II: Buoyancy due to liquefaction The net upward force per unit length of pipeline can be calculated as The extent of liquefaction Lb = 50m Fb =

πD 2 (γ sat − γ content ) − πDtγ pipe 4

Fb = ̟ x 0.7622/4 (18000-0)-̟ x 0.762 x 0.0064 x 78560 = 7005.05N/m It is assumed that the weight of gas flowing through pipe has negligible weight. The unit weight of steel pipe (γpipe) is taken as 78560N/m3. The bending stress in the pipeline due to uplift force (Fb) can be calculated as σ bf = ±

Fb L2b 10 Z

Where Lb = length of pipe in buoyancy zone Z = section modulus of pipe cross section π 0.762 4 − 0.7492 4 = 32 0.762 = 0.0028459m4

(

)

σbf = ± 7005.05 x 502/ (10 x 0.0028459) = 615360117N/m2 Maximum strain in pipe corresponding to the above bending stress calculated as r  σ bf  n  σ bf   1+ E  1 + r  σ y     10 615360117  10  615360117   = 1 +     2 × 1011  1 + 12  413 × 10 6  

ε=

= 0.130705674 The operational strain in the pipeline = εoper = 0.0012505 The total longitudinal strain in the pipe in tension = 0.130705674+ 0.0012505 = 0.1319562 The total longitudinal strain in the pipe in compression = 0.130705674- 0.0012505 = 0.1294551

37

Vulnerability Assessment of Buried Pipelines The allowable strain in pipe in tension is = 3% =0.03 The allowable strain in pipe in compression is Εcr-c = 0.175t/R = 0.175 x 0.0064/0.381 = 0.0029396 The maximum strain in the pipeline due to buoyancy effect is greater than the allowable strain for steel pipes in tension and compression. Case III: Fault Crossing Here the pipeline crosses a normal slip fault with fault displacement of 1.5m and a dip angle of 350. The pipeline crosses the fault line at an angle of 400. The source to site distance can be considered as 20km. The expected normal-slip fault displacement = δfn = 1.5m Dip angle of the fault movement ψ = 350 The angle between pipeline and fault line β = 400 Component of fault displacement in the axial direction of the pipeline δ fax= δ fn cos ψ sin β = 1.5 cos 350 x sin 400 = 0.789811m

Component of fault displacement in transverse direction of pipeline: δ fax= δ fn cos ψ cos β = 1.5 cos 350 x cos 400 = 0.94126m Importance factor for fault movement for pipe = Ip = 2.3 Applying importance factor, The design fault displacement in axial direction becomes = δfax – design = δfax x Ip = 0.789811 x 2.3 = 1.816565707m The design fault displacement in transverse direction becomes = δftr – design = δftr x Ip = 0.94126 x 2.3 = 2.164898707m The average pipe strain due to fault movement in axial direction can be calculated as

38


 δ fax − design 1  δ ftr − design  2    ε = 2 +  2  2L a    2L a  Where La = effective unanchored length of the pipeline in the fault zone E i ε y πDt La = tu 2× 1011 × 0 . 002× π × 0 . 762× 0 . 0064 = 91144

= 67.238m Or La =the actual length of anchorage = 120m Hence, the anchored length to be considered is the lower the above two values. So La = 67.238m Axial strain in the pipe 2  1.8165 1  2.164   ε = 2×  +     2 × 67.238 2  2 × 67.238  

= 0.02728 The operational strain in the pipeline = εoper = 0.0013 Total strain in pipe in tension = 0.0306 + 0.0013 = 0.0285 The allowable strain in pipe in tension is 3% = 0.03 The total tensile strain in pipe due to fault crossing is less than the allowable strain.

Case IV: Seismic wave propagation The expected peak ground acceleration of the site at base rock layer = PGAr = 0.45g For this soil Peak ground acceleration (PGA) at ground = 0.45g x Ig = 0.45g x 0.9 = 0.405g Converting the soil as soft and the magnitude of design basis earthquake (M) is equals to 6.5, and distance of site from earthquake source is about 20km PGV = 0.405 x 140 = 56.7cm/s

39

Vulnerability Assessment of Buried Pipelines Converting the soil as soft and the magnitude of design basis earthquake (M) is equals to 6.5, and distance of site from earthquake source is about 20km PGV = 0.405 x 140 = 56.7cm/s Design peak ground velocity = Vg = PGV x Ip = 56.7 x 1.5 = 85.05cm/sec =0.85m/s Maximum axial strain in the pipe due to wave velocity can be calculated as εa =

Vg αεC

=

0.85 = 0.00021 2 × 2000

Maximum axial strain that can be transmitted by soil friction can be calculated as Maximum axial strain in the pipe due to wave velocity can be calculated as εa =

Vg αεC

=

0.85 = 0.00021 2 × 2000

Maximum axial strain that can be transmitted by soil friction can be calculated as ε a=

tu λ 4 AE

=

91144× 1000 4× 0 . 0151922× 2× 10 11

= 0.00750 The calculated axial strain due to wave passage need not be larger than the strain transmitted by soil friction. The operational strain in the pipeline = εoper = 0.0013 The total strain in pipe in tension = 0.00750 + 0.0013 = 0.00146 The allowable strain in pipe in tension is 3% = 0.03 The maximum strain in pipe due to wave propagation pipe is less than the allowable strain.

40

Vulnerability Assessment of Buried Pipelines Table 4. Maximum strains in the pipe in compression and tension in four cases

Case

Maximum strain in pipe in tension

Maximum strain in pipe in compression

Allowable strain in pipe in tension

Allowable strain in pipe in compression

Safe/Unsafe

I II III IV

0.0027595 0.131956 0.0285 0.00146

0.0002595 0.1294551 ---

0.03 0.03 0.03 0.03

0.0029396 0.0029396 0.0029396 0.0029396

Safe Unsafe Safe Safe

Location 2: The continuous buried pipeline is designed to carry natural gas at a pressure of 9.3MPa. The pipe is of API X-60 grade with 30-in (0.762m) diameter (D) and 0.0103 m wall thickness (t). The installation temperature and operating temperature of the pipeline are 300 C and 650 C respectively. The pipeline is buried at 1.5m of soil cover. Poisson’s ratio and coefficient of thermal expansion of the pipe material can be considered as 0.3 and 12 x 10-6 respectively. This pipeline is checked for four cases they are Case I: Permanent ground displacement (PGD) Case II: Buoyancy due to liquefaction Case III: Fault crossing Case IV: Seismic wave propagation For API X-60 Grade pipe: Yield stress of pipe material = σy = 413 MPa Ramberg-Osgood parameters n = 10 and r =12. Pipe strain due to internal pressure is calculated as follows The longitudinal stress induced in the pipe due to internal pressure will be S p=

PD µ 9300000 × 0.762 × 0.3 = 2t 2 × 0.0103

=103.2 x 106 N/m2 = 103.2MPa

41

Vulnerability Assessment of Buried Pipelines Using Ramberg-Osgood’s stress-strain relationship the longitudinal strain in the pipe will be S Sp  1 + n  p εp = E  1 + r  σ y 

   

r

   

 103.2 × 10 6  10 1+ = 11  1 + 12 2 × 10 

 103.2 × 10 6   413 × 10 6 

   

12

   

= 0.000516 = 0.0516% (tensile) Pipe strain due to temperature change: The longitudinal stress induced in the pipe due to change in temperature will be ST = Eα (T2 – T1) = 2 x 1011 x 12 x 10-6 (65-30) = 84 MPa Using Ramberg-Osgood’s stress-strain relationship the longitudinal strain in the pipe will be S εt = t E

 S 1 + n  t  1 + r  σ y 

   

r

   

84 × 10 6  109  84 × 10 6   1 + = 2 × 1011  1+ 12  413 × 10 6 

  

12

  

= 0.00042 = 0.042% (tensile) The total strain in the continuous pipeline due to internal pressure and temperature is = 0.0516 + 0.042 = 0.0936%. Ignoring the strain in pipe due to installation imperfection or initial bending, the above calculated strain can be considered as the operational strain in pipe (i.e., εoper = 0.0936%).

42

Vulnerability Assessment of Buried Pipelines Case I: Permanent ground displacement (PGD) The permanent ground deformation refers to the unrecoverable soil displacement due to faulting, landslide, settlement or liquefaction induced lateral spreading.

Figure 12. a) Pipeline crossing parallel to the ground movement. b) Pipeline crossing transverse to the ground movement Here the length and width of PGD zone is 120m and 50m respectively. Soil is sandy soil with an angle of friction (Φ) = 320 and effective unit weight of 18 kN/m3. The ground displacement (δl and δt) due to liquefaction can be taken as 2m. The operational strain in pipeline = 0.125% (tensile) Yield stress of pipe material σy = 413 Ramberg-Osgood parameter (n) = 10 Ramberg-Osgood parameter (r) = 12 Parallel crossing (Longitudinal PGD) The expected amount of permanent ground movement parallel to pipe axis = δl = 2m The design ground movement = δl design = δl x Ip = 2 x 1.5 = 3m Case-1: The amount of ground movement (δl design) is considered to be large and the pipe strain is controlled by length (L) of permanent ground deformation zone. The peak pipe strain is calculated as

43


t L εa = u 2π DtE

  tu L 1 + n   1 + r  2π Dt σ y 

   

r

   

Where tu = maximum axial soil force per unit length of pipe for soil condition. The maximum axial soil resistance (tu) per unit length of pipe can be calculated as  1+ K 0  1 t u = πDcα + πDH γ  tan δ 2   Where D = diameter of pipe = 0.762m C = Coefficient of cohesion = 30kpa α = Adhesion Factor = 0.608-0.123 x 0.3 – 0.27/(0.33+1) + 0.695 /(0.33 +1) = 0.99645 H = soil cover above the centre of the pipeline = 1.5m Interface angle of friction between soil and pipe δ1 = f Φ Here f = friction factor = 0.7 for smooth steel pipe δ1 = f Φ = 0.7 x 32o = 22.4o K0 = coefficient of soil pressure at rest = 1- sin 32o = 0.47 tu = ̟ x 0.762 x 30000 x 0.99645 + (̟ x 0.762 x 1.5 x 18000 x ((1+0.47)/2)tan22.4o = 91144N/m =91.144kN/m 12  91144 × 120 10  91144 × 120   εa = 1 +     2 × π × 0.762 × 0.0103 × 2 × 10 11  1 + 12  2 × π × 0.762 × 0.0103 × 413 × 10 6   = 0.001109 = 0.1109% Case-2: The length (L) of permanent ground deformation zone is large, and the pipe strain is controlled by the amount of ground movement (δl design). The peak pipe strain for this case is calculated as t L εa = u e 2π DtE

  t L 1 + n  u e  1 + r  2π Dt σ y 

   

r

   

Where Le = Effective length of pipeline over which the friction force (tu) acts, which can be calculated by the following equation.

44


δ

l design

t L2 = u e πDtE

  t L 1 +  2  n  u e   2 + r  1 + r  πDtσ y 

   

r

   

From this effective length of pipeline is calculated as Le = 150m εa = 0.0015095 The design strain in pipe is taken as the least value between the two cases = εseismic = 0.001446 The operational strain in the pipeline = εoper = 0.000936 The total tensile strain in the pipeline = 0.001446 + 0.000936 = 0.00205 Total compression strain = 0.001446 – 0.000936 = 0.0001734 The limiting strain in tension for permanent ground deformation is = 0.03 The total strain in pipe due to longitudinal strain is less than the allowable strain. Transverse Crossing: The expected amount of transverse permanent ground deformation (δt) = 2m The design transverse ground displacement = δt design = δt x Ip = 2 x 1.5 = 3m. The maximum bending strain in the pipe is calculated as the least value of the following two a)

εb = ±

t πDδ design

W2

= ±̟ x 0.762 x 3 / 502 = ± 0.00287267 b)

PuW 2 εb = ± 3πEtD2

Where Pu = maximum resistance of soil in transverse direction. The maximum transverse soil resistance per unit length of pipe is Pu = N ch cD + N qh γ HD

Where Nch = Horizontal bearing capacity factor for clay

45


N ch = a + bx +

c

(x +1)

2

+

d

(x +1)3

≤9

Where x = H/D = 1.5/0.762 = 1.968503937 a = 6.752 b = 0.065 c = - 11.063 d = 7.119 Nch =6.752+ (0.065 x 1.96) + (-11.063/(1.96+1)2) + (7.119/(1.96+1)3) = 5.896 Nqh = Horizontal bearing capacity factor for sandy soil Nqh = a + bx +cx2 + dx3 + ex4 Where x = H/D = 1.5/0.762 = 1.968503937 a = 5.465 b = 1.548 c = - 0.1118 d = 5.625 x 10-3 e = -1.2227 x 10-4 Hence, Nqh = 5.465 + (1.548 x 1.96) + (-0.1118 x 1.962) + (5.625 x 10-3 x 1.963) + (-1.2227 x 10-4 x 1.964) = 8.120 Hence Pu =5.896 x 30000 x 0.762+ (8.120 x 18000 x 1.5 x 0.762) = 301869N/m = 301.869kN/m 301869× 50 2 ε b= ± 3× π × 2× 1011 × 0 . 0103× 0 . 762 2 = 0.06694 Hence, the maximum strain induced in the pipeline due to transverse PGD is taken as Εseismic = ± 0.00287267 (tensile/compressive) The operational strain in the pipeline = εoper = 0.000936 Total longitudinal strain in the pipe in tension 0.00287267+0.000936= 0.0038 Total longitudinal strain in the pipe in compression = 0.00287267-0.000936= 0.0019 The allowable strain in tension for permanent ground deformation is = 3% = 0.03 The allowable strain in compression for steel pipe is

46

Vulnerability Assessment of Buried Pipelines Εcr-c = 0.175t/R = 0.175 x 0.0103/0.381 = 0.004731 The total strain in pipe due to transverse PGD is less than the allowable strain for both tension and compression. Case II: Buoyancy due to liquefaction The net upward force per unit length of pipeline can be calculated as The extent of liquefaction Lb = 50m πD 2 Fb = (γ sat − γ content ) − πDtγ pipe 4 Fb = ̟ x 0.7622/4 (18000-0)-̟ x 0.762 x 0.0103 x 78560 = 6271.60N/m It is assumed that the weight of gas flowing through pipe has negligible weight. The unit weight of steel pipe (γpipe) is taken as 78560N/m3. The bending stress in the pipeline due to uplift force (Fb) can be calculated as

Fb L2b σ bf = ± 10 Z Where Lb = length of pipe in buoyancy zone Z = section modulus of pipe cross section 0 . 762 4 − 0 . 7414 4  π  = 32 0 . 762 = 0.0045101m4 σbf = ± 7005.05 x 502/ (10 x 0.0045101) =347640990N/m2 Maximum strain in pipe corresponding to the above bending stress calculated as σ σ bf  1 + n  bf ε= E  1 + r  σ y 

=

   

r

   

347640990  10  347640990  1 +   11 1 + 12  413 × 10 6  2 × 10 

10 

 

= 0.001976968 The operational strain in the pipeline = εoper = 0.000936 The total longitudinal strain in the pipe in tension = 0.001976968+ 0.000936= 0.002913 The total longitudinal strain in the pipe in compression = 0.001976968- 0.000936= 0.001041

47

Vulnerability Assessment of Buried Pipelines The allowable strain in pipe in tension is = 3% =0.03 The allowable strain in pipe in compression is Εcr-c = 0.175t/R = 0.175 x 0.0103/0.381 = 0.004731 The maximum strain in the pipeline due to buoyancy effect is greater than the allowable strain for steel pipes in tension and compression. Case III: Fault Crossing Here the pipeline crosses a normal slip fault with fault displacement of 1.5m and a dip angle of 350. The pipeline crosses the fault line at an angle of 400. The source to site distance can be considered as 20km. The expected normal-slip fault displacement = δfn = 1.5m Dip angle of the fault movement ψ = 350 The angle between pipeline and fault line β = 400 Component of fault displacement in the axial direction of the pipeline δ fax= δ fn cos ψ sin β = 1.5 cos 350 x sin 400 = 0.789811m


48


 δ fax − design 1  δ ftr − design  2    ε = 2 +  2  2L a    2L a  Where La = effective unanchored length of the pipeline in the fault zone L a=

E i ε y π Dt tu

2 × 10 11 × 0.002 × π × 0.762 × 0.0103 = 91144 = 108.212m

Or La =the actual length of anchorage = 120m Hence, the anchored length to be considered is the lower the above two values. So La = 108.21m Axial strain in the pipe 2  1.8165 1  2.164   ε = 2× +     2 × 108.21 2  2 × 108.21  

= 0.01689 The operational strain in the pipeline = εoper =0.00094 Total strain in pipe in tension = 0.01689+ 0.00094= 0.0178 The allowable strain in pipe in tension is 3% = 0.03 The total tensile strain in pipe due to fault crossing is less than the allowable strain. Case IV: Seismic wave propagation The expected peak ground acceleration of the site at base rock layer = PGAr = 0.45g For this soil Peak ground acceleration (PGA) at ground = 0.45g x Ig = 0.45g x 0.9 = 0.405g Converting the soil as soft and the magnitude of design basis earthquake (M) is equals to 6.5, and distance of site from earthquake source is about 20km PGV = 0.405 x 140 = 56.7cm/s Design peak ground velocity = Vg = PGV x Ip = 56.7 x 1.5 = 85.05cm/sec =0.85m/s

49

Vulnerability Assessment of Buried Pipelines Maximum axial strain in the pipe due to wave velocity can be calculated as εa =

Vg αεC

=

0.85 = 0.00021 2 × 2000

Maximum axial strain that can be transmitted by soil friction can be calculated as

εa =

tu λ 91144×1000 = 4 AE 4 × 0.0243238× 2 ×1011 = 0.00468

The calculated axial strain due to wave passage need not be larger than the strain transmitted by soil friction. The operational strain in the pipeline = εoper = 0.00094 The total strain in pipe in tension = 0.00468 + 0.00094= 0.00146 The allowable strain in pipe in tension is 3% = 0.03 The maximum strain in pipe due to wave propagation pipe is less than the allowable strain. Table 5. Maximum strains in the pipe in compression and tension in four cases

Case





Safe/Unsafe

I II III IV

0.0020 0.00291 0.0178 0.00115

-0.00104 ---

0.03 0.03 0.03 0.03

0.00473 0.00473 0.00473 0.00473

Safe Safe Unsafe Safe

Location 3: The continuous buried pipeline is designed to carry natural gas at a pressure of 9.3MPa. The pipe is of API X-60 grade with 30-in (0.762m) diameter (D) and 0.0175 m wall thickness (t). The installation temperature and operating temperature of the pipeline are 300 C and 650 C respectively. The pipeline is buried at 1.5m of soil cover. Poisson’s ratio and coefficient of thermal expansion of the pipe material can be considered as 0.3 and 12 x 10-6 respectively. This pipeline is checked for four cases they are Case I: Permanent ground displacement (PGD)

50

Vulnerability Assessment of Buried Pipelines Case II: Buoyancy due to liquefaction Case III: Fault crossing Case IV: Seismic wave propagation For API X-60 Grade pipe: Yield stress of pipe material = σy = 413 MPa Ramberg-Osgood parameters n = 10 and r =12. Pipe strain due to internal pressure is calculated as follows The longitudinal stress induced in the pipe due to internal pressure will be S p=

9300000× 0 . 762× 0 .3 PD µ 2× 0 . 0175 2t =

=60.74 x 106 N/m2 = 60.74MPa Using Ramberg-Osgood’s stress-strain relationship the longitudinal strain in the pipe will be S Sp  1 + n  p εp = E  1 + r  σ y 

   

 60.7 × 10 6  10 1+ = 11  1 + 12 2 × 10 

r

     60.7 × 10 6   413 × 10 6 

   

12

   

= 0.0003035 = 0.03035% (tensile) Pipe strain due to temperature change: The longitudinal stress induced in the pipe due to change in temperature will be ST = Eα (T2 – T1) = 2 x 1011 x 12 x 10-6 (65-30) = 84 MPa Using Ramberg-Osgood’s stress-strain relationship the longitudinal strain in the pipe will be

51


S εt = t E

 S 1 + n  t  1 + r  σ y 

   

r

   

84 × 10 6  109  84 × 10 6   1 + = 2 × 1011  1+ 12  413 × 10 6 

  

12

  

= 0.00042 = 0.042% (tensile) The total strain in the continuous pipeline due to internal pressure and temperature is = 0.03035 + 0.042 = 0.07235%. Ignoring the strain in pipe due to installation imperfection or initial bending, the above calculated strain can be considered as the operational strain in pipe (i.e., εoper = 0.07235%). Case I: Permanent ground displacement (PGD) The permanent ground deformation refers to the unrecoverable soil displacement due to faulting, landslide, settlement or liquefaction induced lateral spreading.

Figure 13. a) Pipeline crossing parallel to the ground movement. b) Pipeline crossing transverse to the ground movement.

52

Vulnerability Assessment of Buried Pipelines Here the length and width of PGD zone is 120m and 50m respectively. Soil is sandy soil with an angle of friction (Φ) = 320 and effective unit weight of 18 kN/m3. The ground displacement (δl and δt) due to liquefaction can be taken as 2m. The operational strain in pipeline = 0.125% (tensile) Yield stress of pipe material σy = 413 Ramberg-Osgood parameter (n) = 10 Ramberg-Osgood parameter (r) = 12

Parallel crossing (Longitudinal PGD) The expected amount of permanent ground movement parallel to pipe axis = δl = 2m The design ground movement = δl design = δl x Ip = 2 x 1.5 = 3m Case-1: The amount of ground movement (δl design) is considered to be large and the pipe strain is controlled by length (L) of permanent ground deformation zone. The peak pipe strain is calculated as t L εa = u 2π DtE

  tu L 1 + n   1 + r  2π Dt σ y 

   

r

   

Where tu = maximum axial soil force per unit length of pipe for soil condition. The maximum axial soil resistance (tu) per unit length of pipe can be calculated as  1+ K 0  1 t u = πDcα + πDH γ  tan δ  2  Where D = diameter of pipe = 0.762m C = Coefficient of cohesion = 30kpa α = Adhesion Factor = 0.608-0.123 x 0.3 – 0.27/(0.33+1) + 0.695 /(0.33 +1) = 0.99645 H = soil cover above the centre of the pipeline = 1.5m Interface angle of friction between soil and pipe δ1 = f Φ Here f = friction factor = 0.7 for smooth steel pipe δ1 = f Φ = 0.7 x 32o = 22.4o K0 = coefficient of soil pressure at rest

53

Vulnerability Assessment of Buried Pipelines = 1- sin 32o = 0.47 tu = ̟ x 0.762 x 30000 x 0.99645 + (̟ x 0.762 x 1.5 x 18000 x ((1+0.47)/2)tan22.4o = 91144N/m =91.144kN/m 12  91144 × 120 10  91144 × 120   εa =    1 + 2 × π × 0.762 × 0.0175 × 2 × 10 11  1 + 12  2 × π × 0.762 × 0.0175 × 413 × 10 6   = 0.000653= 0.0653% Case-2: The length (L) of permanent ground deformation zone is large, and the pipe strain is controlled by the amount of ground movement (δl design). The peak pipe strain for this case is calculated as t L  n  t u L e ε a = u e 1 + 2π DtE  1 + r  2π Dt σ y 

   

r

   

Where Le = Effective length of pipeline over which the friction force (tu) acts, which can be calculated by the following equation. δ

l design

t L2   2  n  t u Le = u e 1 +    πDtE   2 + r  1 + r  πDtσ y 

   

r

   

From this effective length of pipeline is calculated as Le = 252m εa = 0.0013784 The design strain in pipe is taken as the least value between the two cases = εseismic = 0.0006527 The operational strain in the pipeline = εoper = 0.000724 The total tensile strain in the pipeline = 0.0006527+ 0.000724= 0.00138 Total compression strain = 0.0006527– 0.000724= -0.0000710 The limiting strain in tension for permanent ground deformation is = 0.03 The total strain in pipe due to longitudinal strain is less than the allowable strain. Transverse Crossing: The expected amount of transverse permanent ground deformation (δt) = 2m The design transverse ground displacement = δt design = δt x Ip = 2 x 1.5 = 3m. The maximum bending strain in the pipe is calculated as the least value of the following two

54


c)

ε b= ±

d)

ε b= ±

π Dδ tdesign

W2 = ±̟ x 0.762 x 3 / 502 = ± 0.00287267

Pu W2 3π EtD 2


Where Nch = Horizontal bearing capacity factor for clay c d N ch = a + bx + + ≤9 2 (x +1) (x +1)3 Where x = H/D = 1.5/0.762 = 1.968503937 a = 6.752 b = 0.065 c = - 11.063 d = 7.119 Nch =6.752+ (0.065 x 1.96) + (-11.063/(1.96+1)2) + (7.119/(1.96+1)3) = 5.896 Nqh = Horizontal bearing capacity factor for sandy soil Nqh = a + bx +cx2 + dx3 + ex4 Where x = H/D = 1.5/0.762 = 1.968503937 a = 5.465 b = 1.548 c = - 0.1118 d = 5.625 x 10-3 e = -1.2227 x 10-4 Hence, Nqh = 5.465 + (1.548 x 1.96) + (-0.1118 x 1.962) + (5.625 x 10-3 x 1.963) + (-1.2227 x 10-4 x 1.964) = 8.120 Hence Pu =5.896 x 30000 x 0.762+ (8.120 x 18000 x 1.5 x 0.762)

55

Vulnerability Assessment of Buried Pipelines = 301869N/m = 301.869kN/m

εb = ±

301869 × 50 2 3 × π × 2 × 10 11 × 0.0175 × 0.762 2

= 0.03940 Hence, the maximum strain induced in the pipeline due to transverse PGD is taken as Εseismic = ± 0.00287267 (tensile/compressive) The operational strain in the pipeline = εoper = 0.000724 Total longitudinal strain in the pipe in tension 0.00287267+0.000724= 0.0036 Total longitudinal strain in the pipe in compression = 0.00287267-0.000724 = 0.0021 The allowable strain in tension for permanent ground deformation is = 3% = 0.03 The allowable strain in compression for steel pipe is Εcr-c = 0.175t/R = 0.175 x 0.0175/0.381 = 0.0080381 The total strain in pipe due to transverse PGD is less than the allowable strain for both tension and compression. Case II: Buoyancy due to liquefaction The net upward force per unit length of pipeline can be calculated as The extent of liquefaction Lb = 50m 2

F b=

πD − π Dt γ γ sat − γ content 4

pipe

Fb = ̟ x 0.7622/4 (18000-0)-̟ x 0.762 x 0.0175 x 78560 = 4917.54N/m It is assumed that the weight of gas flowing through pipe has negligible weight. The unit weight of steel pipe (γpipe) is taken as 78560N/m3. The bending stress in the pipeline due to uplift force (Fb) can be calculated as F b L 2b σ bf = ± 10 Z Where Lb = length of pipe in buoyancy zone Z = section modulus of pipe cross section π 0.762 4 − 0.727 4 = 32 0.762 = 0.0074474m4

(

)

56

Vulnerability Assessment of Buried Pipelines σbf = ± 7005.05 x 502/ (10 x 0.0028459) = 165074740N/m2 Maximum strain in pipe corresponding to the above bending stress calculated as σ σ bf  1 + n  bf ε= E  1 + r  σ y 

=

   

r

   

165074740  10  165074740  1 +   11 6 2 × 10  1 + 12  413 × 10 

10 

 

= 0.00082544 The operational strain in the pipeline = εoper = 0.0007237

The total longitudinal strain in the pipe in tension = 0.00082544+ 0.0007237= 0.0015492 The total longitudinal strain in the pipe in compression = 0.00082544- 0.0007237= 0.0001017 The allowable strain in pipe in tension is = 3% =0.03 The allowable strain in pipe in compression is Εcr-c = 0.175t/R = 0.175 x 0.0175/0.381 = 0.0080381 The maximum strain in the pipeline due to buoyancy effect is greater than the allowable strain for steel pipes in tension and compression. Case III: Fault Crossing Here the pipeline crosses a normal slip fault with fault displacement of 1.5m and a dip angle of 350. The pipeline crosses the fault line at an angle of 400. The source to site distance can be considered as 20km. The expected normal-slip fault displacement = δfn = 1.5m Dip angle of the fault movement ψ = 350 The angle between pipeline and fault line β = 400 Component of fault displacement in the axial direction of the pipeline δ fax= δ fn cos ψ sin β = 1.5 cos 350 x sin 400 = 0.789811m

57

Vulnerability Assessment of Buried Pipelines Component of fault displacement in transverse direction of pipeline: δ fax= δ fn cos ψ cos β = 1.5 cos 350 x cos 400 = 0.94126m Importance factor for fault movement for pipe = Ip = 2.3 Applying importance factor, The design fault displacement in axial direction becomes = δfax – design = δfax x Ip = 0.789811 x 2.3 = 1.816565707m The design fault displacement in transverse direction becomes = δftr – design = δftr x Ip = 0.94126 x 2.3 = 2.164898707m The average pipe strain due to fault movement in axial direction can be calculated as

 δ fax − design 1  δ ftr − design  2    ε = 2 +  2L 2 2L  a a    Where La = effective unanchored length of the pipeline in the fault zone L a=

E i ε y π Dt tu

2 × 10 11 × 0.002 × π × 0.762 × 0.0175 91144 = 183.855m

=

Or La =the actual length of anchorage = 120m Hence, the anchored length to be considered is the lower the above two values. So La = 120m Axial strain in the pipe  1.8165 1  2.164  2  ε = 2×  +     2 × 120 2  2 × 120  

= 0.01522 The operational strain in the pipeline = εoper = 0.00072 Total strain in pipe in tension = 0.01522 + 0.00072= 0.0159 The allowable strain in pipe in tension is 3% = 0.03

58

Vulnerability Assessment of Buried Pipelines The total tensile strain in pipe due to fault crossing is less than the allowable strain. Case IV: Seismic wave propagation The expected peak ground acceleration of the site at base rock layer = PGAr = 0.45g For this soil Peak ground acceleration (PGA) at ground = 0.45g x Ig = 0.45g x 0.9 = 0.405g Converting the soil as soft and the magnitude of design basis earthquake (M) is equals to 6.5, and distance of site from earthquake source is about 20km PGV = 0.405 x 140 = 56.7cm/s Design peak ground velocity = Vg = PGV x Ip = 56.7 x 1.5 = 85.05cm/sec =0.85m/s Maximum axial strain in the pipe due to wave velocity can be calculated as ε a=

Vg αεC

=

0 . 85 = 0 . 00021 2× 2000


εa =

tu λ 91144× 1000 = 4 AE 4 × 0.040931× 2 ×1011 = 0.00278


Case





Safe/Unsafe

I

0.0014

--

0.03

0.00804

Safe

59

Vulnerability Assessment of Buried Pipelines II III IV

0.00155 0.0159 0.00094

0.00010 ---

0.03 0.03 0.03

0.00804 0.00804 0.00804

Safe Unsafe Safe

Location 4: The continuous buried pipeline is designed to carry natural gas at a pressure of 9.3MPa. The pipe is of API X-60 grade with 18-in (0.4572m) diameter (D) and 0.0103 m wall thickness (t). The installation temperature and operating temperature of the pipeline are 300 C and 650 C respectively. The pipeline is buried at 1.5m of soil cover. Poisson’s ratio and coefficient of thermal expansion of the pipe material can be considered as 0.3 and 12 x 10-6 respectively. This pipeline is checked for four cases they are Case I: Permanent ground displacement (PGD) Case II: Buoyancy due to liquefaction Case III: Fault crossing Case IV: Seismic wave propagation For API X-60 Grade pipe: Yield stress of pipe material = σy = 413 MPa Ramberg-Osgood parameters n = 10 and r =12. Pipe strain due to internal pressure is calculated as follows The longitudinal stress induced in the pipe due to internal pressure will be S p=

PD µ 9300000 × 0.4572 × 0.3 2t = 2 × 0.0103

=61921747.6N/m2 = 61.92MPa Using Ramberg-Osgood’s stress-strain relationship the longitudinal strain in the pipe will be S Sp  1 + n  p εp = E  1 + r  σ y 

=

   

r

   

61921747.6  10  61921747.6  1 +   11 1 + 12  413 × 10 6  2 × 10 

12 

 

60

Vulnerability Assessment of Buried Pipelines = 0.00031= 0.03096% (tensile) Pipe strain due to temperature change: The longitudinal stress induced in the pipe due to change in temperature will be ST = Eα (T2 – T1) = 2 x 1011 x 12 x 10-6 (65-30) = 84 MPa Using Ramberg-Osgood’s stress-strain relationship the longitudinal strain in the pipe will be S  n  S t ε t = t 1 + E  1 + r  σ y 

   

r

   

84 × 10 6  109  84 × 10 6   1 + = 2 × 1011  1+ 12  413 × 10 6 

  

12

  

= 0.00042 = 0.042% (tensile) The total strain in the continuous pipeline due to internal pressure and temperature is = 0.03096 + 0.042 = 0.07296%. Ignoring the strain in pipe due to installation imperfection or initial bending, the above calculated strain can be considered as the operational strain in pipe (i.e., εoper = 0.07296%). Case I: Permanent ground displacement (PGD) The permanent ground deformation refers to the unrecoverable soil displacement due to faulting, landslide, settlement or liquefaction induced lateral spreading.

61


Figure 14. a) Pipeline crossing parallel to the ground movement. b) Pipeline crossing transverse to the ground movement. Here the length and width of PGD zone is 120m and 50m respectively. Soil is sandy soil with an angle of friction (Φ) = 320 and effective unit weight of 18 kN/m3. The ground displacement (δl and δt) due to liquefaction can be taken as 2m. The operational strain in pipeline = 0.125% (tensile) Yield stress of pipe material σy = 413 Ramberg-Osgood parameter (n) = 10 Ramberg-Osgood parameter (r) = 12

Parallel crossing (Longitudinal PGD) The expected amount of permanent ground movement parallel to pipe axis = δl = 2m The design ground movement = δl design = δl x Ip = 2 x 1.5 = 3m Case-1: The amount of ground movement (δl design) is considered to be large and the pipe strain is controlled by length (L) of permanent ground deformation zone. The peak pipe strain is calculated as  tu L t L  1 + n  εa = u 2π DtE  1 + r  2π Dt σ y 

   

r

   

Where tu = maximum axial soil force per unit length of pipe for soil condition.

62


The maximum axial soil resistance (tu) per unit length of pipe can be calculated as  1+ K 0  1 t u = πDcα + πDH γ  tan δ  2  Where D = diameter of pipe = 0.4572m C = Coefficient of cohesion = 30kpa α = Adhesion Factor = 0.608-0.123 x 0.3 – 0.27/(0.33+1) + 0.695 /(0.33 +1) = 0.99645 H = soil cover above the centre of the pipeline = 1.5m Interface angle of friction between soil and pipe δ1 = f Φ Here f = friction factor = 0.7 for smooth steel pipe δ1 = f Φ = 0.7 x 32o = 22.4o K0 = coefficient of soil pressure at rest = 1- sin 32o = 0.47 tu = ̟ x 0.4572 x 30000 x 0.99645 + (̟ x 0.4572 x 1.5 x 18000 x ((1+0.47)/2)tan22.4o = 54686.4N/m =54.6864kN/m 91144 × 120 εa = 2 × π × 0.4572 × 0.0103 × 2 × 10 11

12  10  91144 × 120    1 + 6    1 + 12  2 × π × 0.4572 × 0.0103 × 413 × 10  

= 0.001109 = 0.1109% Case-2: The length (L) of permanent ground deformation zone is large, and the pipe strain is controlled by the amount of ground movement (δl design). The peak pipe strain for this case is calculated as t L  n  t u L e ε a = u e 1 + 2π DtE  1 + r  2π Dt σ y 

   

r

   


l design

t L2 = u e πDtE

  t L 1 +  2  n  u e   2 + r  1 + r  πDtσ y 

   

r

   

From this effective length of pipeline is calculated as Le = 155m εa = 0.001446

63

Vulnerability Assessment of Buried Pipelines The design strain in pipe is taken as the least value between the two cases = εseismic = 0.001446 The operational strain in the pipeline = εoper = 0.000730 The total tensile strain in the pipeline = 0.001446 + 0.000730= 0.00184 Total compression strain = 0.001446 – 0.000730= 0.0003798 The limiting strain in tension for permanent ground deformation is = 0.03 The total strain in pipe due to longitudinal strain is less than the allowable strain. Transverse Crossing: The expected amount of transverse permanent ground deformation (δt) = 2m The design transverse ground displacement = δt design = δt x Ip = 2 x 1.5 = 3m. The maximum bending strain in the pipe is calculated as the least value of the following two e)

ε b= ±

f)

εb = ±

π Dδ tdesign

W2 = ±̟ x 0.4572 x 3 / 502 = ± 0.0017236

PuW 2 3πEtD2


Where Nch = Horizontal bearing capacity factor for clay c d N ch = a + bx + + ≤9 2 (x +1) (x +1)3 Where x = H/D = 1.5/0.4572 = 1.968503937 a = 6.752 b = 0.065 c = - 11.063

64

Vulnerability Assessment of Buried Pipelines d = 7.119 Nch =6.752+ (0.065 x 1.96) + (-11.063/(1.96+1)2) + (7.119/(1.96+1)3) = 5.896 Nqh = Horizontal bearing capacity factor for sandy soil Nqh = a + bx +cx2 + dx3 + ex4 Where x = H/D = 1.5/0.4572 = 1.968503937 a = 5.465 b = 1.548 c = - 0.1118 d = 5.625 x 10-3 e = -1.2227 x 10-4 Hence, Nqh = 5.465 + (1.548 x 1.96) + (-0.1118 x 1.962) + (5.625 x 10-3 x 1.963) + (-1.2227 x 10-4 x 1.964) = 8.120 Hence Pu =5.896 x 30000 x 0.4572+ (8.120 x 18000 x 1.5 x 0.4572) = 206083N/m = 206.083kN/m

εb = ±

206083 × 50 2 3 × π × 2 × 10 11 × 0.0103 × 0.762 2

= 0.12695 Hence, the maximum strain induced in the pipeline due to transverse PGD is taken as Εseismic = ± 0.0017236(tensile/compressive) The operational strain in the pipeline = εoper = 0.000730 Total longitudinal strain in the pipe in tension 0.0017236+0.000730= 0.0025 Total longitudinal strain in the pipe in compression = 0.0017236-0.000730= 0.0010 The allowable strain in tension for permanent ground deformation is = 3% = 0.03 The allowable strain in compression for steel pipe is Εcr-c = 0.175t/R = 0.175 x 0.0103/0.2286 = 0.007885 The total strain in pipe due to transverse PGD is less than the allowable strain for both tension and compression. Case II: Buoyancy due to liquefaction 65

Vulnerability Assessment of Buried Pipelines The net upward force per unit length of pipeline can be calculated as The extent of liquefaction Lb = 50m πD 2 Fb = (γ sat − γ content ) − πDtγ pipe 4 Fb = ̟ x 0.45722/4 (18000-0)-̟ x 0.4572 x 0.0103 x 78560 = 1792.88N/m It is assumed that the weight of gas flowing through pipe has negligible weight. The unit weight of steel pipe (γpipe) is taken as 78560N/m3. The bending stress in the pipeline due to uplift force (Fb) can be calculated as

Fb L2b σ bf = ± 10 Z Where Lb = length of pipe in buoyancy zone Z = section modulus of pipe cross section π 0.4572 4 − 0.4366 4 = 32 0.4572 = 0.0015801m4

(

)

σbf = ± 1792.88 x 502/ (10 x 0.0015801) = 283667011N/m2 Maximum strain in pipe corresponding to the above bending stress calculated as σ σ bf  1 + n  bf ε= E  1 + r  σ y 

=

   

r

   

615360117  10  615360117  1 +   11 1 + 12  413 × 10 6  2 × 10 

10 

 

= 0.001443828 The operational strain in the pipeline = εoper = 0.0007296 The total longitudinal strain in the pipe in tension = 0.001443828+ 0.0007296 = 0.0021734 The total longitudinal strain in the pipe in compression = 0.001443828- 0.0007296= 0.0007142 The allowable strain in pipe in tension is = 3% =0.03 The allowable strain in pipe in compression is Εcr-c = 0.175t/R = 0.175 x 0.0103/0.2286 = 0.007885

66

Vulnerability Assessment of Buried Pipelines The maximum strain in the pipeline due to buoyancy effect is greater than the allowable strain for steel pipes in tension and compression. Case III: Fault Crossing Here the pipeline crosses a normal slip fault with fault displacement of 1.5m and a dip angle of 350. The pipeline crosses the fault line at an angle of 400. The source to site distance can be considered as 20km. The expected normal-slip fault displacement = δfn = 1.5m Dip angle of the fault movement ψ = 350 The angle between pipeline and fault line β = 400 Component of fault displacement in the axial direction of the pipeline δ fax= δ fn cos ψ sin β = 1.5 cos 350 x sin 400 = 0.789811m


 δ fax − design 1  δ ftr − design  2    ε = 2 +  2  2L a    2L a  Where La = effective unanchored length of the pipeline in the fault zone E i ε y πDt La = tu

67

Vulnerability Assessment of Buried Pipelines 2× 1011× 0 . 002× π × 0 . 4572× 0 . 0103 = 54686 . 39314

= 108.212m Or La =the actual length of anchorage = 120m Hence, the anchored length to be considered is the lower the above two values. So La = 108.21m Axial strain in the pipe 2  1.8165 1  2.164   ε = 2× +     2 × 108.21 2  2 × 108.21  

= 0.01689 The operational strain in the pipeline = εoper = 0.00073 Total strain in pipe in tension = 0.01689 + 0.00073= 0.0285 The allowable strain in pipe in tension is 3% = 0.03 The total tensile strain in pipe due to fault crossing is less than the allowable strain. Case IV: Seismic wave propagation The expected peak ground acceleration of the site at base rock layer = PGAr = 0.45g For this soil Peak ground acceleration (PGA) at ground = 0.45g x Ig = 0.45g x 0.9 = 0.405g Converting the soil as soft and the magnitude of design basis earthquake (M) is equals to 6.5, and distance of site from earthquake source is about 20km PGV = 0.405 x 140 = 56.7cm/s Design peak ground velocity = Vg = PGV x Ip = 56.7 x 1.5 = 85.05cm/sec =0.85m/s Maximum axial strain in the pipe due to wave velocity can be calculated as ε a=

Vg αεC

=

0 . 85 = 0 . 00021 2× 2000


68


εa =

tu λ 54686.39314 × 1000 = 4 AE 4 × 0.014461× 2 ×1011 = 0.00473


Case





Safe/Unsafe

I II III IV

0.0018 0.00217 0.0176 0.0094

-0.00071 ---

0.03 0.03 0.03 0.03

0.00788 0.00788 0.00788 0.00788

Safe Safe Unsafe Safe

Location 5: The continuous buried pipeline is designed to carry natural gas at a pressure of 9.3MPa. The pipe is of API X-60 grade with 24-in (0.6096m) diameter (D) and 0.0127 m wall thickness (t). The installation temperature and operating temperature of the pipeline are 300 C and 650 C respectively. The pipeline is buried at 1.5m of soil cover. Poisson’s ratio and coefficient of thermal expansion of the pipe material can be considered as 0.3 and 12 x 10-6 respectively. This pipeline is checked for four cases they are Case I: Permanent ground displacement (PGD) Case II: Buoyancy due to liquefaction Case III: Fault crossing Case IV: Seismic wave propagation For API X-60 Grade pipe:

69

Vulnerability Assessment of Buried Pipelines Yield stress of pipe material = σy = 413 MPa Ramberg-Osgood parameters n = 10 and r =12. Pipe strain due to internal pressure is calculated as follows The longitudinal stress induced in the pipe due to internal pressure will be S p=

PD µ 9300000 × 0.6096 × 0.3 2t = 2 × 0.0127

=66960000N/m2 = 66.96MPa Using Ramberg-Osgood’s stress-strain relationship the longitudinal strain in the pipe will be S Sp  1 + n  p εp = E  1 + r  σ y  66960000 = 2 × 10 11

   

r

   

12  10  66960000   1 +    6  1 + 12  413 × 10  

= 0.00033= 0.03348% (tensile) Pipe strain due to temperature change: The longitudinal stress induced in the pipe due to change in temperature will be ST = Eα (T2 – T1) = 2 x 1011 x 12 x 10-6 (65-30) = 84 MPa Using Ramberg-Osgood’s stress-strain relationship the longitudinal strain in the pipe will be S  n  S t ε t = t 1 + E  1 + r  σ y 

   

r

   

84 × 10 6  109  84 × 10 6   1 + = 2 × 1011  1+ 12  413 × 10 6 

  

12

  

70

Vulnerability Assessment of Buried Pipelines = 0.00042 = 0.042% (tensile) The total strain in the continuous pipeline due to internal pressure and temperature is = 0.03348 + 0.042 = 0.07548%. Ignoring the strain in pipe due to installation imperfection or initial bending, the above calculated strain can be considered as the operational strain in pipe (i.e., εoper = 0.07548%).

Case I: Permanent ground displacement (PGD) The permanent ground deformation refers to the unrecoverable soil displacement due to faulting, landslide, settlement or liquefaction induced lateral spreading.

Figure 15. a) Pipeline crossing parallel to the ground movement. b) Pipeline crossing transverse to the ground movement. Here the length and width of PGD zone is 120m and 50m respectively. Soil is sandy soil with an angle of friction (Φ) = 320 and effective unit weight of 18 kN/m3. The ground displacement (δl and δt) due to liquefaction can be taken as 2m. The operational strain in pipeline = 0.125% (tensile) Yield stress of pipe material σy = 413

71

Vulnerability Assessment of Buried Pipelines Ramberg-Osgood parameter (n) = 10 Ramberg-Osgood parameter (r) = 12 Parallel crossing (Longitudinal PGD) The expected amount of permanent ground movement parallel to pipe axis = δl = 2m The design ground movement = δl design = δl x Ip = 2 x 1.5 = 3m Case-1: The amount of ground movement (δl design) is considered to be large and the pipe strain is controlled by length (L) of permanent ground deformation zone. The peak pipe strain is calculated as t L εa = u 2π DtE

  tu L 1 + n   1 + r  2π Dt σ y 

   

r

   

Where tu = maximum axial soil force per unit length of pipe for soil condition. The maximum axial soil resistance (tu) per unit length of pipe can be calculated as  1+ K 0  1 t u = πDcα + πDH γ  tan δ 2   Where D = diameter of pipe = 0.6096m C = Coefficient of cohesion = 30kpa α = Adhesion Factor = 0.608-0.123 x 0.3 – 0.27/(0.33+1) + 0.695 /(0.33 +1) = 0.99645 H = soil cover above the centre of the pipeline = 1.5m Interface angle of friction between soil and pipe δ1 = f Φ Here f = friction factor = 0.7 for smooth steel pipe δ1 = f Φ = 0.7 x 32o = 22.4o K0 = coefficient of soil pressure at rest = 1- sin 32o = 0.47 tu = ̟ x 0.6095 x 30000 x 0.99645 + (̟ x 0.6096 x 1.5 x 18000 x ((1+0.47)/2)tan22.4o = 72915.2N/m =72.9152kN/m 12  72915.2 × 120 10  72915.2 × 120   εa =    1 + 2 × π × 0.762 × 0.0127 × 2 × 10 11  1 + 12  2 × π × 0.762 × 0.0127 × 413 × 10 6   = 0.000899= 0.0899%

72

Vulnerability Assessment of Buried Pipelines Case-2: The length (L) of permanent ground deformation zone is large, and the pipe strain is controlled by the amount of ground movement (δl design). The peak pipe strain for this case is calculated as t L εa = u e 2π DtE

  t L 1 + n  u e  1 + r  2π Dt σ y 

   

r

   


l design

t L2   2  n  t u Le = u e 1 +    πDtE   2 + r  1 + r  πDtσ y 

   

r

   

From this effective length of pipeline is calculated as Le = 188m εa = 0.0014201 The design strain in pipe is taken as the least value between the two cases = εseismic = 0.0008994 The operational strain in the pipeline = εoper = 0.000755 The total tensile strain in the pipeline = 0.0008994+ 0.000755= 0.00205 Total compression strain = 0.0008994– 0.000755= 0.0001734 The limiting strain in tension for permanent ground deformation is = 0.03 The total strain in pipe due to longitudinal strain is less than the allowable strain. Transverse Crossing: The expected amount of transverse permanent ground deformation (δt) = 2m The design transverse ground displacement = δt design = δt x Ip = 2 x 1.5 = 3m. The maximum bending strain in the pipe is calculated as the least value of the following two g)

ε b= ±

π Dδ tdesign

W2 = ±̟ x 0.6096 x 3 / 502 = ± 0.00229814

73


h)

εb = ±

PuW 2 3πEtD2


Where Nch = Horizontal bearing capacity factor for clay c d N ch = a + bx + + ≤9 2 (x +1) (x +1)3 Where x = H/D = 1.5/0.6096 = 1.968503937 a = 6.752 b = 0.065 c = - 11.063 d = 7.119 Nch =6.752+ (0.065 x 1.96) + (-11.063/(1.96+1)2) + (7.119/(1.96+1)3) = 5.896 Nqh = Horizontal bearing capacity factor for sandy soil Nqh = a + bx +cx2 + dx3 + ex4 Where x = H/D = 1.5/0.6096 = 1.968503937 a = 5.465 b = 1.548 c = - 0.1118 d = 5.625 x 10-3 e = -1.2227 x 10-4 Hence, Nqh = 5.465 + (1.548 x 1.96) + (-0.1118 x 1.962) + (5.625 x 10-3 x 1.963) + (-1.2227 x 10-4 x 1.964) = 8.120 Hence Pu =5.896 x 30000 x 0.762+ (8.120 x 18000 x 1.5 x 0.762) = 255467N/m = 255.467kN/m

74


εb = ±

255467 × 50 2 3 × π × 2 × 1011 × 0.0127 × 0.6096 2

= 0.07179 Hence, the maximum strain induced in the pipeline due to transverse PGD is taken as Εseismic = ± 0.0022981 (tensile/compressive) The operational strain in the pipeline = εoper = 0.000755 Total longitudinal strain in the pipe in tension 0.0022981 +0.000755= 0.0038 Total longitudinal strain in the pipe in compression = 0.0022981 -0.000755= 0.0019 The allowable strain in tension for permanent ground deformation is = 3% = 0.03 The allowable strain in compression for steel pipe is Εcr-c = 0.175t/R = 0.175 x 0.0127/0.3048 = 0.0072917 The total strain in pipe due to transverse PGD is less than the allowable strain for both tension and compression. Case II: Buoyancy due to liquefaction The net upward force per unit length of pipeline can be calculated as The extent of liquefaction Lb = 50m πD 2 Fb = (γ sat − γ content ) − πDtγ pipe 4 Fb = ̟ x 0.60962/4 (18000-0)-̟ x 0.6096 x 0.0127 x 78560 = 3342.81N/m It is assumed that the weight of gas flowing through pipe has negligible weight. The unit weight of steel pipe (γpipe) is taken as 78560N/m3. The bending stress in the pipeline due to uplift force (Fb) can be calculated as F L2 σ bf = ± b b 10 Z Where Lb = length of pipe in buoyancy zone Z = section modulus of pipe cross section 0 . 60964 − 0 . 58424  π  = 32 0 . 6096 = 0.0034814m4 σbf = ± 7005.05 x 502/ (10 x 0.0028459) = 240050032N/m2

75

Vulnerability Assessment of Buried Pipelines Maximum strain in pipe corresponding to the above bending stress calculated as σ σ bf  1 + n  bf ε= E  1 + r  σ y 

=

   

r

   

240050032  10  240050032  1 +   11 6 2 × 10  1 + 12  413 × 10 

10 

 

= 0.001204313

The operational strain in the pipeline = εoper = 0.0007548 The total longitudinal strain in the pipe in tension = 0.001204313+ 0.0007548= 0.0019591 The total longitudinal strain in the pipe in compression = 0.001204313- 0.0007548= 0.0004495 The allowable strain in pipe in tension is = 3% =0.03 The allowable strain in pipe in compression is Εcr-c = 0.175t/R = 0.175 x 0.0127/0.3048 = 0.0072917 The maximum strain in the pipeline due to buoyancy effect is greater than the allowable strain for steel pipes in tension and compression. Case III: Fault Crossing Here the pipeline crosses a normal slip fault with fault displacement of 1.5m and a dip angle of 350. The pipeline crosses the fault line at an angle of 400. The source to site distance can be considered as 20km. The expected normal-slip fault displacement = δfn = 1.5m Dip angle of the fault movement ψ = 350 The angle between pipeline and fault line β = 400 Component of fault displacement in the axial direction of the pipeline δ fax= δ fn cos ψ sin β = 1.5 cos 350 x sin 400 = 0.789811m

Component of fault displacement in transverse direction of pipeline: δ fax= δ fn cos ψ cos β = 1.5 cos 350 x cos 400 = 0.94126m 76

Vulnerability Assessment of Buried Pipelines Importance factor for fault movement for pipe = Ip = 2.3 Applying importance factor, The design fault displacement in axial direction becomes = δfax – design = δfax x Ip = 0.789811 x 2.3 = 1.816565707m The design fault displacement in transverse direction becomes = δftr – design = δftr x Ip = 0.94126 x 2.3 = 2.164898707m The average pipe strain due to fault movement in axial direction can be calculated as

 δ fax − design 1  δ ftr − design  2    ε = 2 +  2  2L a    2L a  Where La = effective unanchored length of the pipeline in the fault zone E i ε y πDt La = tu 2× 1011× 0 . 002× π × 0 . 6096× 0 . 0127 = 72915 . 19086

= 133.426m Or La =the actual length of anchorage = 120m Hence, the anchored length to be considered is the lower the above two values. So La = 120m Axial strain in the pipe  1.8165 1  2.164  2  ε = 2×  +     2 × 120 2  2 × 120  

= 0.01522 The operational strain in the pipeline = εoper = 0.00075

Total strain in pipe in tension =0.01522 + 0.00075= 0.0285 The allowable strain in pipe in tension is 3% = 0.03 The total tensile strain in pipe due to fault crossing is less than the allowable strain.

77


Case IV: Seismic wave propagation The expected peak ground acceleration of the site at base rock layer = PGAr = 0.45g For this soil Peak ground acceleration (PGA) at ground = 0.45g x Ig = 0.45g x 0.9 = 0.405g Converting the soil as soft and the magnitude of design basis earthquake (M) is equals to 6.5, and distance of site from earthquake source is about 20km PGV = 0.405 x 140 = 56.7cm/s Design peak ground velocity = Vg = PGV x Ip = 56.7 x 1.5 = 85.05cm/sec =0.85m/s Maximum axial strain in the pipe due to wave velocity can be calculated as Vg

ε a=

αεC

=

0 . 85 = 0 . 00021 2× 2000


tu λ 91144×1000 = 4 AE 4 × 0.0238153× 2 ×1011

εa =

= 0.00383 The calculated axial strain due to wave passage need not be larger than the strain transmitted by soil friction. The operational strain in the pipeline = εoper = 0.00075 The total strain in pipe in tension = 0.00383+ 0.00075= 0.000967 The allowable strain in pipe in tension is 3% = 0.03 The maximum strain in pipe due to wave propagation pipe is less than the allowable strain. Table 8. Maximum strains in the pipe in compression and tension in four cases

Case





Safe/Unsafe

I II

0.0017 0.00196

-0.00045

0.03 0.03

0.00729 0.00729

Safe Safe

78

Vulnerability Assessment of Buried Pipelines III IV

0.0160 0.00097

---

0.03 0.03

0.00729 0.00729

Unsafe Safe

6.2 Parametric Studies Four pipelines of different diameters as 12”, 18”, 24” and 30” which are operating under the same pressure of 7.5 Mpa. The installation temperature and operating temperature of the pipeline are 300 and 600C respectively. The pipe is of API X-52 grade with different thicknesses. Poisson’s ratio and coefficient of thermal expansion of the pipe material can be considered as 0.3 and 12 x 10-6 respectively. The unit weight of saturated soil at the site is 18 kN/m3. The pipeline crosses a normal slip fault with fault displacement of 1.5m, 2.5m and a dip angle of 350. The pipeline crosses the fault line at an angle of 400. The source to site distance can be considered as 20km. The expected peak ground acceleration (PGA) in the site is 0.45g at the base rock layer. Table 9. Strains due to internal pressure and temperature change with pipe wall thickness for pipe diameter is 12” Pipe wall thickness(mm) 6.4 7.1 8.7 10.3 11.1 12.7 14.3 17.5 20.6

Strain due to internal pressure 0.00027 0.00024 0.00020 0.00017 0.00015 0.00014 0.00012 0.00010 0.00008

79

Strain due to temperature change 0.00036 0.00036 0.00036 0.00036 0.00036 0.00036 0.00036 0.00036 0.00036

Total strain 0.00063 0.0006 0.00056 0.00053 0.00051 0.0005 0.00048 0.00046 0.00044


Figure 16. Total strain vs pipe thickness for pipe diameter is 12 “ Table 10. Strains due to internal pressure and temperature change with pipe wall thickness for pipe diameter is 18” Pipe wall thickness(m m) 6.4 7.1 8.7 10.3 11.1 12.7 14.3 17.5 20.6

Strain due to internal pressure

Strain due to temperature change

Total strain

0.00040 0.00036 0.00030 0.00025 0.00023 0.00020 0.00018 0.00015 0.00012

0.00036 0.00036 0.00036 0.00036 0.00036 0.00036 0.00036 0.00036 0.00036

0.00076 0.00072 0.00066 0.00061 0.00059 0.00056 0.00054 0.00051 0.00048

80


Figure 17. Total strain vs pipe thickness for pipe diameter is 18 “ Table 11. Strains due to internal pressure and temperature change with pipe wall thickness for pipe diameter is 24” Pipe wall thickness(m m) 6.4 7.1 8.7 10.3 11.1 12.7 14.3 17.5 20.6

Strain due to internal pressure

Strain due to temperature change

Total strain

0.00054 0.00048 0.00039 0.00033 0.00031 0.00027 0.00024 0.00020 0.00017

0.00036 0.00036 0.00036 0.00036 0.00036 0.00036 0.00036 0.00036 0.00036

0.0009 0.00084 0.00075 0.00069 0.00067 0.00063 0.0006 0.00056 0.00053

81


Figure 18. Total strain vs pipe thickness for pipe diameter is 24 “ Table 12. Strains due to internal pressure and temperature change with pipe wall thickness for pipe diameter is 30” Pipe wall Strain due to internal Strain due to thickness(m Total strain pressure temperature change m) 6.4 0.00067 0.00036 0.00103 7.1 0.00060 0.00036 0.00096 8.7 0.00049 0.00036 0.00085 10.3 0.00042 0.00036 0.00078 11.1 0.00039 0.00036 0.00075 12.7 0.00034 0.00036 0.0007 14.3 0.00030 0.00036 0.00066 17.5 0.00024 0.00036 0.0006 20.6 0.00021 0.00036 0.00057

82


Figure 19. Total strain vs pipe thickness for pipe diameter is 30 “ Buoyancy due to liquefaction: Buoyancy due to liquefaction for Pipe diameter = 12” Table 13. Longitudinal strains in the pipe due to tension and compression for pipe diameter is 12” Pipe wall thickness (mm)

Buoyancy force N/m

6.4 7.1 8.7 10.3 11.1 12.7 14.3 17.5 20.6

831.94 779.28 658.92 538.56 478.38 358.02 237.66 -3.06 -236.26

Total longitudinal strain in the pipe in tension 0.0023854 0.0019325 0.0014629 0.0011613 0.0010419 0.0008455 0.000689858 0.000455688 0.000288917

Total longitudinal strain in the pipe in compression 0.0011296 0.0007295 0.0003487 0.0001083 0.00001293 -0.00014449 -0.00026993 -0.00046026 -0.00059754

83

The allowable strain in pipe in tension 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03

The allowable strain in pipe in compression 0.0073491 0.0081529 0.009902 0.011827 0.0127461 0.0145833 0.0164206 0.0200951 0.0236549

Safe/ Unsafe Safe Safe Safe Safe Safe Safe Safe Safe Safe

Vulnerability Assessment of Buried Pipelines Table 14. Longitudinal strains in the pipe due to tension and compression for pipe diameter is 18” Pipe wall thickness (mm)

Buoyancy force N/m

6.4 7.1 8.7 10.3 11.1 12.7 14.3 17.5 20.6

2232.95 2153.96 1973.42 1792.88 1702.61 1522.07 1341.53 980.44 630.64


Total longitudinal strain in the pipe in compression 0.002331932 0.00112524 0.00052854 0.00029889 0.00021267 0.00007251 -0.00003750 -0.000200525 -0.000313917


The allowable strain in pipe in compression 0.0048994 0.0054353 0.0066601 0.0078850 0.0084974 0.0097222 0.0109471 0.0133968 0.0157699

Safe/ Unsafe Safe Safe Safe Safe Safe Safe Safe Safe Safe

Table 15. Longitudinal strains in the pipe due to tension and compression for pipe diameter is 24” Pipe wall thickness (mm)

Buoyancy force N/m

6.4

4290.65

7.1 8.7 10.3 11.1 12.7 14.3 17.5 20.6

4185.34 3944.62 3703.89 3583.53 3342.81 3102.09 2620.64 2154.24


Total longitudinal strain in the pipe in compression 0.00376660 0.00152824 0.00058557 0.00034777 0.00026698 0.00013829 0.000038351 -0.000108383 -0.000209064

84

The allowable strain in pipe in tension

The allowable strain in pipe in compression

0.03

0.0036745

0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03

0.0040764 0.0049951 0.0059137 0.0063730 0.0072917 0.0082103 0.0100476 0.0118274

Safe/ Unsafe Unsafe in comp Safe Safe Safe Safe Safe Safe Safe Safe

Vulnerability Assessment of Buried Pipelines Table 16. Longitudinal strains in the pipe due to tension and compression for pipe diameter is 30” Pipe wall thickness (mm)

Buoyancy force N/m

6.4

7005.05

7.1 8.7 10.3 11.1 12.7 14.3 17.5 20.6

6873.40 6572.50 6271.6 6121.15 5820.24 5519.34 4917.54 4334.54


Total longitudinal strain in the pipe in compression 0.00512147 0.00189989 0.00059712 0.00034413 0.00026728 0.00014816 0.000056740 -0.00007669 -0.00016763

The allowable strain in pipe in tension

The allowable strain in pipe in compression

0.03

0.0029396

0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03

0.0032612 0.0039961 0.0047310 0.0050984 0.0058333 0.0065682 0.0080381 0.0094619

Safe/ Unsafe Unsafe in comp Safe Safe Safe Safe Safe Safe Safe Safe

Fault Crossing Table 17. Total strains in the pipe due to tension Pipe diameter is 12” and fault displacement 1.5m Pipe wall thickness (mm) 6.4 7.1 8.7 10.3 11.1 12.7 14.3 17.5 20.6

Total strain in the pipe in tension 0.0267 0.0241 0.0197 0.0188 0.0188 0.0188 0.0188 0.0188 0.0188


Safe/Unsafe Safe Safe Safe Safe Safe Safe Safe Safe Safe

Table 18. Total strains in the pipe due to tension Pipe diameter is 18” and fault displacement 1.5m Pipe wall thickness (mm) 6.4

Total strain in the pipe in tension 0.0269

85

The allowable strain in pipe in tension 0.03

Safe/Unsafe Safe

Vulnerability Assessment of Buried Pipelines 7.1 8.7 10.3 11.1 12.7 14.3 17.5 20.6

0.0242 0.0198 0.0189 0.0189 0.0188 0.0188 0.0188 0.0188

0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03

Safe Safe Safe Safe Safe Safe Safe Safe

Table 19. Total strains in the pipe due to tension Pipe diameter is 24” and fault displacement 1.5m Pipe wall thickness (mm) 6.4 7.1 8.7 10.3 11.1 12.7 14.3 17.5 20.6






86



Vulnerability Assessment of Buried Pipelines Table 21. Total strains in the pipe due to tension Pipe diameter is 12” and fault displacement 2.5m Pipe wall thickness (mm) 6.4 7.1 8.7 10.3 11.1 12.7 14.3 17.5 20.6



Safe/Unsafe Unsafe in tension Unsafe in tension Unsafe in tension Unsafe in tension Unsafe in tension Unsafe in tension Unsafe in tension Unsafe in tension Unsafe in tension





Table 23. Total strains in the pipe due to tension Pipe diameter is 24” and fault displacement 2.5m Pipe wall thickness (mm) 6.4 7.1 8.7 10.3 11.1 12.7

Total strain in the pipe in tension 0.0446 0.0402 0.0328 0.0313 0.0313 0.0312

87

The allowable strain in pipe in tension 0.03 0.03 0.03 0.03 0.03 0.03

Safe/Unsafe Unsafe in tension Unsafe in tension Unsafe in tension Unsafe in tension Unsafe in tension Unsafe in tension

Vulnerability Assessment of Buried Pipelines 14.3 17.5 20.6

0.0312 0.0312 0.0311

0.03 0.03 0.03

Unsafe in tension Unsafe in tension Unsafe in tension





Seismic Wave Propagation: Table 25. Total strains in the pipe due to tension Pipe diameter is 12” and PGA =0.45g Pipe wall thickness (mm) 6.4 7.1 8.7 10.3 11.1 12.7 14.3 17.5 20.6




Table 26. Total strains in the pipe due to tension Pipe diameter is 18” and PGA =0.45g Pipe wall thickness (mm) 6.4 7.1

Total strain in the pipe in tension 0.000974 0.000935

88

The allowable strain in pipe in tension 0.03 0.03

Safe/Unsafe Safe Safe

Vulnerability Assessment of Buried Pipelines 8.7 10.3 11.1 12.7 14.3 17.5 20.6

0.000868 0.000822 0.000804 0.000775 0.000752 0.00072 0.000697

0.03 0.03 0.03 0.03 0.03 0.03 0.03

Safe Safe Safe Safe Safe Safe Safe

Table 27. Total strains in the pipe due to tension Pipe diameter is 24” and PGA =0.45g Pipe wall thickness (mm) 6.4 7.1 8.7 10.3 11.1 12.7 14.3 17.5 20.6




Table 28. Total strains in the pipe due to tension Pipe diameter is 30” and PGA =0.45g Pipe wall thickness (mm) 6.4 7.1 8.7 10.3 11.1 12.7 14.3 17.5 20.6




The rapid expansion of natural gas transmission pipelines in order to convey this vital energy source to the rapidly expanding economies in Asia brings many challenges, one of which is the design and construction of these pipelines to mitigate the threat of seismic instability. Gujarat is one of the most highly earthquake prone states in India. In

89

Vulnerability Assessment of Buried Pipelines the last few years many state owned and private organizations have constructed pipeline networks across the state, bringing the challenge of designing in such an area into sharp focus. Ruptures or severe distortions of pipelines are most often associated with relative motion arising from fault movements, landslides, liquefaction, loss of support, or differential motion at abrupt interfaces between rock and soil. The most catastrophic damages are those resulting from faulting and liquefaction. This paper illustrates the performance of high pressure gas pipelines under test conditions of fault movement and soil liquefaction which were generated by changing parameters such as Diameter, thickness, depth of cover and fault displacement. Based on the results from the study recommendations have been derived which aim to minimize the consequences of earthquakes/tremors on existing and planned pipelines. Recommendations include updating of geotechnical data into GIS systems and design and construction modifications, which are applicable to all pipelines operating, or proposed to operate, in areas of seismic instability. Modern pipelines wither onshore or offshore, are typically buried to provide protection and support. Buried pipelines are normally designed on the basis of hoop stress limitations for internal pressure. For pipelines subjected to large temperature differentials, special stress analysis may be required for bend configurations. In addition, buried pipelines may require design for external loads, e.g., loads imparted by heavy equipment at ground surface. During earthquake, a buried pipeline may experience significant loading as a result of large relative displacement of the ground along its length. Large ground movements caused by faulting, liquefaction, lateral spreading, landslides and slope failure. The exposure to these hazards can be minimized through careful selection of a pipeline route, especially in the case of such localized conditions as slope failure. However, faulting and liquefaction – induced movements, such as lateral spreading, often cannot avoid on long pipeline routes through areas of high seismicity.

7. Conclusions In the design of a pipeline for crossing a fault line, the following considerations generally will improve the capability of the pipeline to withstand differential movement. 1. The pipelines crossing fault line should be oriented in such a way to avoid compression in the pipeline. The optimum angle of fault crossing will depend upon the dip plane and the expected type of movement. And it should be within 90 degree 2. Pipeline ductility should be increased in fault-crossing region to accommodate large fault movement without rapture.

90

Vulnerability Assessment of Buried Pipelines 3. Abrupt changes in wall thickness should be avoided within fault zone. 4. In all areas of potential ground rapture, pipelines should be laid in relatively straight section avoiding sharp changes in direction and elevation. 5. To the extent possible, pipelines should be constructed without field bends, elbows, and flanges that tend to anchor the pipeline to the ground. 6. If longer length of pipeline is available to conform to fault movement, level of strain gets reduced. Hence, the points of anchorage should be provided away from the fault zone to the extent possible in order to lower the level of strain in the pipeline. 7. A hard and smooth coating on the pipeline such as an epoxy coating may be used in the vicinity of the fault crossing to reduce the angle of friction between pipeline and soil. Example: Three layer of epoxy coating 8. The burial depth of pipeline should be minimized within fault zones in order to reduce soil restrain on the pipeline during fault movement. 9. Pipelines may be placed on the above ground sliding supports. 10. In the design of a pipeline for in the Liquefied zone, the following considerations generally will improve the capability of the pipeline to withstand buoyancy force due to soil liquefaction. 11. Concrete weights or gravel filled balnkets can be utilized to provide additional resistance to buoyancy. 12. The buoyancy effect can also be minimized by shallow burial of the pipeline above the ground water level. 13. Where uplift is the main concern, one may provide anchors at a spacing of up to 150m to prevent uplift. 14. An increase in pipe wall thickness will increase the pipeline’s capacity for buoyancy force due to soil liquefaction. 15. Use of shutoff valves may be increased to protect the pipeline of gas leakage in case of any severe damages.

91


8. References [1] Suresh Ranjan Dash and Sudhir K Jain., (2008), “An overview of seismic considerations of buried pipelines”, Journal of Structural Engineering Vol. 34, No. 5, pp. 349–359. [2] Indranil Guha, “Earthquake Effects on Pipelines”, Joe McGowan Gujarat Gas Company Limited. [3] Suresh R Dash and Sudhir K Jain., (2007), “IITK-GSDMA GUIDELINES for SEISMIC DESIGN of BURIED PIPELINES” IITK GSDMA codes. [4] http://www.gujpetronet.com/ [5] http://www.mapsofindia.com/maps/oilandgasmaps/ [6] www.safan.com

92