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Pipeline In nutshell! Mahdi Haghdoust Structural Engineering (M.Sc) student of Urmia university https://www.researchgate.net/profile/Mahdi_Haghdoust [email protected] [email protected]

What is Pipeline? Is it really that much different?  

Well the answer is no! it’s not that much different. Consider a cylindrical tubular member. This member can be used as a column in an offshore structure or as a beam of a children swing or as a system to transport fuel or water from one place to another. The only thing that differs in these situations is members mechanical behavior. So, when we talk about a pipe, – as a structural engineer of course – we talk about a cylindrical tubular member that carries a fluid. This members – which we will call it pipe hereafter – load bearing capacity, ductility, stiffness degradation and energy dissipation will be discussed. The scenario we define for member determines what kind of behavior is expected.

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More about cylindrical tubular sections The cylindrical tubular members are predominant in offshore structures and Pipelines because of several reasons. They minimize hydrodynamic forces, have great torsional rigidity, offer great local strength against impact loading, and minimize the outside surface subject to corrosion. Above all, they have the same large buckling strength in all directions. However, a joint of tubular members tends to have a complicated configuration which results in high stress concentration. The high stress concentration causes cumulative fatigue failure due to cyclic wave forces. For this reason, much of the early offshore research was directed towards the study of tubular joint. Copyright©2010 Companyname | Free template by Investintech PDF Solutions

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Cylindrical members design in offshore structures The design of offshore structures is based on the so-called 'dual design philosophy'. This design philosophy consists of two requirements: strength requirements and ductility requirements. The strength requirements are intended to prevent major structural damage for the level of earthquake activity that has a reasonable probability of occurring during the life of a structure. The ductility requirements are intended to ensure that the structure has a sufficient energy absorption and dissipation capacity through an inelastic straining of its component members to prevent a total collapse of the structural system. Copyright©2010 Companyname | Free template by Investintech PDF Solutions

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More about Pipes Contents: 1- Strength of Material 2- Pipe Hydraulics (brief) 3- Design Strategies and Value


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Strength of Material A pipe must have enough strength and/or stiffness to perform its intended function. It must also be durable enough to last for its design life. The term strength as used here is the ability to resist stress. Stresses in a conduit may be caused by such loadings as internal pressure, soil loads, live loads, differential settlement, and longitudinal Bending.


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Strength of Material The term stiffness refers to the material’s ability to resist deflection. Stiffness is directly related to the modulus of elasticity of the pipe material and the second moment of the cross section of the pipe wall. Durability is a measure of the pipe’s ability to withstand environmental effects with time. Such terms as orrosion resistance and abrasion resistance are durability factors.


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Strength of Material Piping materials are generally placed in one of two classifications: rigid or flexible. A flexible pipe has been defined as one that will deflect at least 2 percent without structural distress. Materials that do not meet this criterion are usually considered to be rigid. Claims that a particular pipe is neither flexible nor rigid, but somewhere in between have little importance since current design standards are based either on the concept of a flexible conduit or on the concept of a rigid conduit.


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Strength of Material


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Strength of Material  Concrete and clay pipes are examples of materials which are usually considered to be rigid. Steel and plastic pipes are usually considered to be flexible. Each type of pipe may have one or more performance limits which must be considered by the design engineer. For rigid pipes, strength to resist wall stresses due to the combined effects of internal pressure and external load is usually critical. For flexible pipes, stiffness may be important in resisting ring deflection and possible buckling. Copyright©2010 Companyname | Free template by Investintech PDF Solutions

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Pipe Hydraulics (brief)  Flow in pipes is usually classified as pressure flow for systems where pipes are flowing full or open-channel flow when pipes are not flowing full. Water and Oil systems and are pressure systems and are considered to be flowing full. On the other hand, sewer systems, for the most part, are open-channel systems. The exception to this is forced sewer mains where lift pumps are used to pump sewage under pressure.


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Design  The client and authorities in the country where a pipeline is to be installed shall endorse the codes and standards used by the designer. Pipeline design codes that are widely recognised include:  • ASME B31.8-1999 Chapter VIII;  • BS 8010 Part 3;  • ISO 13623;  • DNV OS-F101.  • API Copyright©2010 Companyname | Free template by Investintech PDF Solutions

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Design  ASME B31.8, BS 8010 Part 3 and ISO 13623 are all codes that belong to the Allowable Stress Design (ASD) family of codes. DNV OS-F101 adopts the Load and Resistance Factor Design (LRFD) format.  Traditionally the following different limit states are considered: • Serviceability Limit States (SLS); • Ultimate Limit States (ULS); • Accidental Limit States (ALS).


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Design- Serviceability Limit States (SLS)  For a marine pipeline it shall be ensured that during its installation and operation it will not be unsuitable for its intended purpose. The SLS refers to a given load condition that, if exceeded, can cause the pipeline to be unsuitable for continued operation. The SLS are defined for all the relevant loading conditions that can be formulated. The following issues are normally considered:  • deformation and movements due to waves and currents (hydrodynamic stability);  • longitudinal deformations due to temperature and pressure variations (pipeline expansion);  • lateral deformations due to restrained temperature and pressure expansion (upheaval buckling or snaking);  • blockage of the pipeline, due to hydrate formation or wax deposition (flow ssurance), for example. Copyright©2010 Companyname | Free template by Investintech PDF Solutions

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Design- Serviceability Limit States (SLS)


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Design- Ultimate Limit States (ULS)  It shall be ensured that the pipeline has the required safety against failure in the ULS, defined in terms of:  • plastic deformations (yielding);  • local instability (buckling);  • crack instability (bursting);  • repeated loading (fatigue).  Furthermore, it shall be ensured that the pipeline has the required safety against accidental loads. Copyright©2010 Companyname | Free template by Investintech PDF Solutions

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Design- Ultimate Limit States (ULS)  The design criteria for ULS should in general be formulated for the first passage of the limit state, as the first passage in almost all cases is equivalent to failure. Note, however, that yielding failure is defined in terms of deformations, not stresses, implying that first time yield is allowed, provided it does not lead to excessive strains or deformations.  It should also be noted that fatigue or other time dependent deterioration mechanisms reduce the strength of the structure, and may initiate ULS. In this relation it is useful to distinguish between damage tolerant and amage intolerant structures. For the latter, fatigue may be treated as an ULS, whereas it may be considered as an SLS for a damage tolerant structure. Copyright©2010 Companyname | Free template by Investintech PDF Solutions

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Design- Ultimate Limit States (ULS)


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Resources :  A. Moser, Steve Folkman-Buried Pipe Design, 3rd Edition (2008)  M.W. Braestrup-Design And Installation Of Marine Pipelines-Blackwell Science (2005)  API-API RP 1111 4th Ed. Dec. 2009 - Design, Construction, Operation, and Maintenance of Offshore Hydrocarbon Pipelines  WSAA 2003 Common Failure Modes in Pressurised Pipeline Systems Copyright©2010 Companyname | Free template by Investintech PDF Solutions

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