RECONDITIONING OF DRILL COLLARS BY USING ...

Journal of the Balkan Tribological Association

Vol. 21, No 2, 314–328 (2015)

Wear – reconditioning technology of drill collars

RECONDITIONING OF DRILL COLLARS BY USING WELDING TECHNOLOGIES R. G. RIPEANU*, M. BADICIOIU, M. CALTARU University Petroleum-Gas of Ploiesti, 39 Bucharest Blvd, 100 680 Ploiesti, Romania E-mail: [email protected], [email protected], [email protected], [email protected] a

ABSTRACT During the exploitation process, the drill collars used in the petroleum industry are exposed to an intensive wear that leads to their rejection due to the material loss. Present paper brings forwards the technological procedure, established by the authors, for increasing the life time of the drill collars by applying a compensation material, using the welding technology, onto the damaged surface of the drill collar. The compensation layer (deposited layer) was characterised in order to fulfill the same behaviour like the drill collars, including wear tests. Keywords: drill collars, reconditioning, welding, wear. AIMS AND BACKGROUND The drill collars are the most expensive elements of the drill string and their durability is essential for the economical drill work efficiency. A drill collar is a device used in the drilling of oil wells for weighting the drill bit, enabling it to drill through rock. It is a bar made of solid steel, either plain carbon steel or a nonmagnetic steel alloy, drilled lengthwise to permit the passage of drilling fluids. These devices are typically about 9450 mm long and threaded at both ends (pin and box) to allow multiple drill collars to be joined above the bit assembly. Typically, drill collars will be consistent in length but may vary in diameter, and their outside configuration may be slick or spiral. The outside diameter may vary from about 76 to 279 mm and greater1–3. In the exploitation time, the drill collars are subjected to torsion, tensile/ compression, internal pressure, external pressure and bending. At the same time, * For correspondence.

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original drill collar size

Fig. 1. Drill collar abrasion wear

worn drill collar diameter

radius angle

original elevator shoulder

elevator groove

due to the different environments, the drill collars are subject to degradation processes resulting in rejection of them in a relatively short time (the life of a drill collars is approx. 3 years). Two of the degradation processes that lead to the rapid decline in lifetime are abrasive wear of the external surfaces (due to the friction between the drill collars with the inner surface of the casing or the open hole wall) and internal corrosion (due to the passage of drilling fluids through drill collars). Figure 1 presents the drill collar abrasion wear4. If the wear is advanced, the drill string can slip from the elevator shoulder (device used for handling the drill string) and fall into the borehole. Depending on the existing wear at some point, drill collars are being downgraded to a degree of past (class) lower resistance. If the drill collars cannot be assigned to any class of resistance, it is permanently withdrawn from service (rejected), being considered ‘scrap metal’. Generally, the price of the ‘scrap metal’ is approx. 30 times smaller than the purchase price of the new drill collars. For example, if the price of a new drill collars (nominal diameter 127 mm, grade S135, length 9140 mm, total mass of 32.9 kg/m) is approx. 1800 euro price, the ‘scrap metal’ price reaches a maximum of 60 euro5. In this moment, the number of the drill collars rejected is increasing every day and the price obtained from their sale as ‘scrap metal’ cover only a small part of the amount invested for their purchase5. Figure 2 presents the drill collars after their use6. Based on this, the aim of the present research work is to establish the optimum reconditioning technology of the drill collars, in order to avoid their rejection and to increase their life time. The damage surface of the drill collars is fulfill 315

Fig. 2. Drill collars used

with a basic flux core tubular wire by using metal active gas welding process. The quality of the deposited layer is investigated by performing macroscopic analyses, metallographic analyses, Brinell hardness measurement, microhardness measurement, chemical composition measurement and wear tests. The obtained results have to indicate that the deposited layer (compensation layer) fulfill the same characteristics and behaviour like the drill collars. RECONDITIONING, RESULTS AND DISCUSSION PARENT MATERIAL

The experimental researches regarding the drill collars reconditioning by welding, were performed on specimens having 200 mm length, 180 mm outer diameter, manufactured by steel AISI 4145H (utilised in drill collars construction) (Fig. 3).

Fig. 3. Specimen utilised in the experimental work

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Table 1. Characteristics of the steel AISI 4145H Chemical analysis (%) Fe

C

Si

Mn

P

S

Cr

Mo

Ni

Al

Co

Cu

Nb

Ti

V

96.1 0.488 0.277 1.086 0.018 0.014 1.160 0.323 0.182 0.017 0.011 0.220 0.0005 0.0079 0.0054 Hardness 299HBW (310HV), 305HBW (315HV), 296HBW (299HV)

The characteristics of the AISI 4145H steel, determined on the product, are presented in Table 1. COMPENSATION MATERIAL

In the experimental work it was used a basic flux core tubular wire of 1.2 mm diameter7. The chemical composition and the deposit characteristics are presented in Tables 2 and 3. It is very important to choose the most suitable compensation material because it has to have the same characteristics with the drill collars material in order to have the same behaviour in the exploitation work. Table 2. Chemical composition of the deposit (%) C 0.088

Mn 1.885

Si 0.518

P S Cr 0.0092 0.0049 0.988

Ni 1.755

Mo 0.3954

V 0.0033

Cu 0.0477

Nb 0.0011

Table 3. Mechanical characteristics of the deposit Yield strength Rp0.2 (N/mm 2)

Tensile strength Rm (N/mm 2)

Elongation A (%)

940

10 0 0

16

The metal active gas welding process (MAG) was used to reconditioning the damage drill collars. The shielding gas was 82% Ar and 18% CO2 (trade mark Corgon@18). WELDING EQUIPMENT

For the experimental research work, welding equipment was designed and manufactured which allowed, from the cinematic point of view, the following movements: continuous rotation of the specimen, axial feed of the welding torch, oscillate the welding torch8–10. Figure 4 shows a scheme of the welding equipment used in the experimental work. The welding equipment has the following components: –  constant direct current (DC) power supply capable of furnishing a current of 180–400 A and 20–30 V, with the wire positive (DCEP); –  griping and rotating device able to grip and rotate the heavy weight drill pipe at a constant rotating speed of between 0.2 to 1.2 rpm; 317

17° – 19° X = 12–38 mm

welding torch grip and oscillate device electrical drive - cc

Y = 18–25 mm specimen

table

Fig. 4. The welding equipment scheme

–  grip and oscillate device able to oscillate the welding torch parallel to the pipe surface with the amplitude of 15 to 25 mm and at approximately 60 to 90 oscillations per minute, and to incline the welding torch, in the direction of the rotation, between 17–19° as measured from the centre-line of the heavy weight drill pipe. RECONDITIONING BY WELDING METHODOLOGY

In order to reconditioning the damage surface of the drill collars, the following specific welding procedure was applied11: –  Material preparation. After turning the specimen by using a lathe machine a visual inspection of the weld surface was performed to ensure it is clean and without rust, dirt, grease, oil, etc. –  Griping the specimen in the griping and rotating device. –  Reconditioning the specimen by welding. The specimen temperature, before welding process, was around 20°C (without preheating). In order to cover with compensation material, the whole damage area of the drill collar (total length of 160 mm), three welding strata were deposited, each of them having six welding beads consecutive applied (the width of one weld bead is 31±1 mm, and the overlap between two weld beads is 1.5 mm), by using the technological parameters presented in Table 4. The suitable values for the technological parameters of the reconditioning by welding process were established based on the extensive docu318

Table 4. Technological parameters of the reconditioning by welding process Technological parameters Polarity Amperage (A) Voltage (V) Shielding gas (l/min) Filler metal speed (m/min) X distance (from Fig. 2) (mm) Y distance (from Fig. 2) (mm) Rotating speed of the specimen (rot/min) Welding speed (m/h) Oscillating the welding torch:   –  oscillating speed (oscillation/min)   –  oscillation amplitude (mm)

Values reverse/spray arc 220 ± 10 29 ± 1 12 11 20 21 0.33 10.8 60 25

mentary research literature, the recommendations of the compensation materials manufacturer and the preliminary researches made. To avoid the superheating of the parent metal it was necessary to wait until the average temperature of the probe decreases around 150–250°C, before proceeding to the next welding stratum. In Fig. 5 are presented pictures during the reconditioning process. In Fig. 6 are presented different pictures which indicate the temperatures of the probe during the reconditioning by welding process. The temperature of the probe was measured by using an infrared thermographic camera, type FLIR E50. –  Controlled cooling of the specimen. When the reconditioning by welding process was finished, the probe was slowly cooled, to avoid the cracks in the weld beads, by using an isolated thermal blanket having a thickness of 100 mm. –  Quality control. After cooling, the quality of the deposited layer was investigated.

Fig. 5. Pictures during the reconditioning process

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temperature of the probe before applying the second stratum

temperature of the probe after applying the second stratum

temperature of the probe before applying the third stratum

temperature of the probe after applying the third stratum

Fig. 6. Temperatures of the probe before and after applying the second and the third stratum

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RESULTS AND DISCUSSION After cooling, the reconditioned specimens were analysed and tested in order to verify the quality of deposition. The deposition quality was verified by: macroscopic analyses, metallographic analyses by optical microscopy, chemical composition measurement, Brinell and microhardness measurements and wear tests. Macroscopic analyses. The macroscopic analyses were made both on the specimen reconditioned and on the samples cut from the specimen and prepared by polishing and metallographic etching with chemical reactive (NITAL) (Fig. 7b). The investigations have found the following: –  there were no cracks visible to the naked eye in the deposited layers; –  were not identified surface defects after the liquid penetrant nondestructive control; –  the adhesion between the substrate (parent metal) and the deposited layers is good (without discontinuities, porosities, etc.); –  the thickness of the deposited layer is 10±1 mm. Analysis by optical microscopy. The analyses by optical microscopy were performed on metallographic samples A and B cut from the reconditioned specimen prepared by polishing and metallographic etching with chemical reactive (NITAL), as shown in Fig. 7a. The analyses were performed with OLYMPUS BX60M type metallographic microscope.

a

b Fig. 7. Metallographic samples – location for metallographic samples used in optical microscopy analyses; b – sample cut from the reconditioned specimen prepared by polishing and metallographic etching

The metallographic analyses of the reconditioned specimen start from the surfaces of the deposited layer, by mm to mm, until the parent metal (Fig. 8). 321

Surface 1 mm

12 mm

40 mm

Parent metal

1 mm

10 mm

4 mm

5 mm

7 mm

6 mm

40 mm

40 mm

40 mm

40 mm

9 mm

2 mm

40 mm

40 mm

3 mm

40 mm

40 mm

8 mm

40 mm

40 mm

10 mm

12 mm

Fig. 8. Microstructure images starting from the surfaces of the deposited layer until the parent metal

In Fig. 9 are presented microstructure images at a bigger magnification. The investigations have found the following: –  the parent metal has a sorbitic structure outside the influenced thermal area; –  the parent metal in the adjacent weld bead area has a martensitic-bainitic structures (martensitic structure in the transition area to the parent metal; bainitic structure in the adjacent fusion line); 322

Deposited layer

Hardness 361-393 HV0.5

Deposited layer

Hardness 361-393 HV0.5 Influences thermal area (ZIT) Hardness 309-318 HV0.5 400 mm

400 mm

a

b Hardness 361-393 HV0.5

Deposited layer

Hardness 347-351 HV0.5 Parent metal

Fig. 9. Microstructure images of the deposited layer, heat affected zone (ZIT) and parent metal

400 mm

c

–  the deposited layer shows a typical structure for weld deposits with alloys that contains chemical elements which form carbides; –  the adhesion between the substrate (parent metal) and the deposited layer is good (no discontinuities are visible); –  there were no cracks and discontinuities visible; –  were observed some nonmetallic inclusions, probably due to incomplete removal of the slag (Fig. 9c); it is very important to remove very carefully the slag resulted in the welding process, before proceeding the next welding bead. Determination the chemical composition of the parent metal and the deposited layer. In order to establish the chemical composition of the parent metal and the deposited layer, the investigations were performed with FONDRY MASTER PRO type laboratory spectrometer. The results obtained are shown in Table 5. Table 5. Chemical composition of the parent metal and deposited layer (%) Fe

C

Si

Mn

P

S

Cr

Mo

Ni

Al

Co

Cu

Nb

Ti

V

Parent metal 96.1 0.488 0.277 1.086 0.018 0.014 1.160 0.323 0.182 0.017 0.011 0.220 0.0005 0.0079 0.0054 Deposited layer 95.44 0.479 0.319 1.289 0.0178 0.014 1.116 0.347 0.555 0.022 0.009 0.183 0.0005 0.0088 0.0053

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At the end of the reconditioned process, the chemical compositions are almost the same in deposited layer and parent metal, which indicates that the reconditioning technology applied for repair the damage drill collars, is adequate. Brinell hardness measurements. The Brinell hardness tests were performed with ROCKY TH-160 type hardness machines at a load 187.5 kgf, using a tungsten carbide penetrator, having 2.5 mm diameter. The investigations have found the following hardness values: –  in parent metal: 299HBW (310HV), 305HBW (315HV), 296HBW (299HV); –  in deposited layer: 305HBW (315HV), 299HBW (310HV), 311HBW (321HV). At the end of the reconditioned process, the hardness is almost the same in deposited layer and parent metal, which indicates that the reconditioning technology applied for repair the damage drill collars, is adequate.

hardness, HV0.5

Microhardness measurements. The micro hardness tests were performed with an EMCO – DURASCAN 20 type microhardness machines at a load 0.5 kgf. The microhardness HV0.5 variation with the distance from the deposited layer to the parent metal is presented in Fig. 10. At the end of the reconditioned process, the 450 400 350 300 250 200 150 100 50 0 0

ZIT parent metal

deposited layer

1

2

3

4

5

6 7 distance (nm)

8

9

10

11

12

13

Fig. 10. Microhardness HV0.5 variation with the distance from the deposited layer to the parent metal

hardness is almost the same in deposited layer, influenced thermal area (ZIT) and parent metal, which confirms again that the reconditioning technology applied for repair the damage drill collars, is adequate. Wear tests. Wear tests were conducted in three steps. The first step consists in establishing electrochemical parameters in formation water for samples made of drill collars parent material (AISI 4145 H) and samples with deposition layers similar as at reconditioning. The second step consists in wear dry tests on ball-ondisk couples on a CSM type tribometer, disk samples were made also from drill collars parent material and with deposition layers similar as at reconditioning. At 324

the third step were tested on ball-on-disk couples in formation water testing medium on a CSM type tribometer, disk samples were made also from drill collars parent material and with deposition layers similar as at reconditioning. Establishing electrochemical parameters. In exploitation processes the drill collars work in aggressive medium. In this order test were conducted in formation water with the main characteristics: pH = 6.6, and the chemical composition with Na+ 79.58 g/l, Caz+ 4.41 g/l, Mgz+ 0.90 g/l, HCO3– 0.92 g/l and Cl– 133 g/l collected from a well water supply tank. There are several electrochemical techniques that can be used to evaluate the behaviour of materials in electrolytic mediums such as12–14: potentiodynamic anodic, cathodic or both polarisation measurements, galvanic corrosion measurements, potentiostatic measurements, linear polarisation, pitting scans, Tafel plots measurements etc. Tafel plots technique quickly yields corrosion rate information. The linear portion of the anodic or cathodic polarisation logarithm current versus potential plot is extrapolated to intersect the corrosion potential line. This permits rapid, high accuracy measurement of extremely low corrosion rates. For this reason to determine electrochemical parameters we used this technique. According to the mixed potential theory12,13, any electrochemical reaction can be divided into two or more oxidation and reduction reactions, and can be no accumulation of electrical charge during the reaction. In a corroding system, corrosion of the metal and reduction of some species in solution is taking place at same rate and the net measurable current, imeas is zero. Electrochemically, corrosion rate measurement is based on the determination of the oxidation current, iox at the corrosion potential, Ecorr. This oxidation current is called the corrosion current, icorr. imeas  = icorr – ired = 0 at Ecorr

(1)

After extraction from drill collars parent material and recondition samples, specimens were machined with small cutting conditions and with cutting fluid in order to avoid the influence above metallographic structure at dimensions ∅16 –0.1 × 3 mm. One sample surface (coated one) was polish with 500 Mesh abrasive papers. Corrosion cell works with a saturated calomel reference electrode and specimen holder exposes 1 cm2 of the specimen to the test solution. Using Tafel plots technique were determined the electrochemical parameters presented in Table 6. Table 6. Results of electrochemical parameters Material

Corrosion potential Ecor (V)

Corrosion current Icor (mA)

Corrosion rate Vcor (mm/a)

Parent material AISI 4145H Deposition layer

0.061 0.115

70.35 70.25

0.826 0.825

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Electrochemical tests were made according to ASTM G5-94 (Ref. 14), and ASTM G1-90 (Ref. 15). The reference electrode was Calomel (Pt/Hg/Hg2Cl2). Corrosion rates obtained show that at recondition by welding, deposition layer has a corrosion behaviour similar with the parent material.

friction coefficient

Wear test on CSM Instruments tribometer. On ball-on-disk microtribometer machine were tested samples made of drill collars parent material (AISI 4145 H) and samples with deposition layers similar as at reconditioning by welding. The working conditions were: –  normal load of 2 N; –  disks of AISI 4145H and of reconditioning by welding; –  ∅6 mm ball of steel 100Cr6; –  sliding speed of 0.100 m/s; –  friction length 100 m; –  dry friction at temperature of air of 20°C and RH = 33% and in formation water. In Fig. 11 it is shown the friction coefficients values results obtained on ballon-disk tribometer. 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

0

20

40 60 friction length (m)

80

100

Parent material AISI 4145H, dry friction

Recondition by welding, dry friction

Parent material AISI 4145H, friction in formation water

Recondition by welding, friction in formation water

Fig. 11. Friction coefficients versus friction length

In Table 7 it is presented the wear rates obtained for tested materials on CSM microtribometer. Table 7. Wear rate coefficients Material type

Parent material AISI 4145H Recondition by welding formation formation Testing medium dry dry water water Disk wear rate coefficient (mm3/N m) 1.207E-005 4.890E-005 2.085E-005 6.877E-005 Ball wear rate coefficient (mm3/N m) 1.756E-005 1.096E-006 1.310E-005 8.162E-007

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As we can see from Fig. 11 and Table 7 the results obtained show that deposition layer behaviour at friction is similar with the parent material. Friction coefficients in dry friction conditions for disk made of recondition by welding has a maximum values of 0.7 comparing with parent material with a maximum friction coefficient value of 0.65. At tests in the presence of formation water the friction coefficients of recondition by welding material were smaller than the values obtained for parent material. The maximum value of friction coefficient for parent material was 0.32 and the maximum value obtained for recondition by welding material was 0.28. Wear rates of deposition stratum was with a small value greater than parent material wear rate. Also in dry and in formation water testing medium CONCLUSIONS Based on experimental researches, the technology and the equipment for drill collars reconditioning were developed. The damage surface of the drill collars was fulfill with a basic flux core tubular wire by using metal active gas welding process. The results of the macroscopic, metallographic analyses, Brinell hardness measurements, microhardness measurement, chemical composition measurements and wear tests indicate that the deposited layer (compensation layer) fulfill the same characteristics and behaviour like the drill collars, which indicate that the developed reconditioning technology is suitable to be applied in order to avoid the drill collars rejection and to increase their life time. ACKNOWLEDGEMENTS The authors are grateful for performing some of experimental tests on equipments acquired by European POS CCE -A2-O2.2.1/860/SMIS/CSNR/14682 project: ‘Regional centre of establishing performance and monitoring the technical state of tubular goods used in petroleum industry’. REFERENCES   1. V. ULMANU: Petroleum Equipment Manufacturing and Repairing Technology. Publ House ILEX, Bucharest, Romania, 2002 (in Romanian).   2. V. ULMANU: Manufacture, Repair and Maintenance of Chemical and Petrochemical Equipment. Teaching and Educational Publ House, Bucharest, Romania, 1981 (in Romanian).   3. V. ULMANU: Petroleum Tubular Materials. Technical Publ House, Bucharest, Romania, 1992 (in Romanian).  4. Recommended Practice for Drill Stem Design and Operating Limits. API Recommended Practice 7G, 16th ed., 1998.

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  5. S. C. TUBEX S.R.L. Bucharest, Daneş (Provides Services for Oil and Gas Industry for over 50 Years) – Information Regarding the New and Used Drill Collars, Romania, 2013.  6. http://www.everypart.com.   7. Basic Flux Core Tubular Wire. Product Data. Oerlikon-Welding Comsumables, 3rd ed.   8. V. ULMANU, M. BADICIOIU, M. CALTARU, GH. ZECHERU, GH. DRAGHICI, M. MINESCU, C. PREDA: Heavy-weight Drill Pipe Hard-facing by Using Welding Technologies. J Balk Tribol Assoc, 16 (4), 510 (2010).   9. V. ULMANU, GH. DRAGHICI, M. BADICIOIU, M. CALTARU, GH. ZECHERU, M. MINESCU: Research Regarding the Surface Hardening of Petroleum Tubulars by Using Welding Technologies. In: Proc. of the 7th International Conference of Technology and Quality for Sustained Development, TQSD 2006, 25–27 May 2006, Bucharest, Romania, 2006, 39–44. 10. Recommended Procedures Manual for the Preparation, Application and Inspection of ARNCO 100XTTM. Hardbanding, Version 1.0. November, 1999. 11. M. BADICIOIU et al.: Research and Development of Reconditioning Technology for Drill Collars. Research Project. Petroleum-Gas University of Ploiesti, Romania, 2013 (in Romanian). 12. F. MANSFIELD: Simultaneous Determination of Instantaneous Corrosion Rates and Tafel Slopes from Polarisation Resistance Measurements. J Electrochem Soc, 120, 515 (1973). 13. W. BAECKMANN, W. SCHWENK, W PRINY: Handbook of Cathodic Protection and the Practice of Electrochemical Corrosion Protection Technique. 3rd ed, Gulf Professional Publishing an Imprint of Elsevier Science, 1997. 14. ASTM G5-94(1999). Standard Reference Test Method for Making Potentiostatic and Potentiodynamic Anodic Polarisation Measurements. ASTM International, West Conshohocken, PA, 1999, www.astm.org. 15. ASTM G1-90(1999)e1. Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens. ASTM International, West Conshohocken, PA, 1999, www.astm.org. Received 14 January 2015 Revised 20 March 2015

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