MECHANICAL AND ENVIRONMENTAL EVALUATION OF TWO COMMERCIAL INTERNAL COATINGS USED IN A 5-INCH DRILL PIPE

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1 Paper No MECHANICAL AND ENVIRONMENTAL EVALUATION OF TWO COMMERCIAL INTERNAL COATINGS USED IN A 5-INCH DRILL PIPE Fengmei Song *, Jim Feiger and Jim Lankford Mechanical and Materials Engineering Southwest Research Institute 6220 Culebra Road San Antonio, TX * fsong@swri.org Junfeng Fang Shanghai Shine Petroleum Pipe Special Coating Material Co., Ltd No. 1825, Luodong Road Baoshan Industry Park, Shanghai, , China ABSTRACT Pipe internal coatings have been developed and used to improve flow efficiency and corrosion resistance of production lines. Accelerated laboratory tests were performed to evaluate the mechanical and environmental resistances of two commercial coatings used in a 135S 5-inch-OD drill pipe. The parameters evaluated include resistances to torsion, flattening, abrasion, and tension, and resistance of one coating to pipe corrosion in high temperature and pressure brines which: (1) have a high ph, (2) contain CO 2, or (3) contain CO 2 and H 2 S. No sign of failure of both coatings was observed after tensile loading test. The wear resistance was below 2.2 liter/μm for both coatings, although the wear patterns after abrasion test were shown to be irregular. After torsional loading and flattening tests, the coatings were shown to have limited degradation, in the form of delamination and disbondment. Examinations of the samples after environmental tests, under 30x optical microscope, showed no coating delamination, while the coating color changed slightly. Keyword: drill pipe, internal coating, corrosion, production, wear resistance INTRODUCTION Many production pipes are made of carbon steel and coated internally to improve flow efficiency and corrosion resistance. Such pipes are often used to operate at elevated temperatures and pressures, Copyright 2009 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole must be in writing to NACE International, Copyright Division, 1440 South creek Drive, Houston, Texas The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association. Printed in the U.S.A. 1 1

2 and carry fluids containing solids, corrosive species such as CO 2 and H 2 S. The harsh operating conditions and environments require that the internal coating possess resistances to wear and be capable of serving as a barrier to resist corrosion. Samples of two commercial coatings, TC2000B TM (Manufacturer 1) and TC2000 TM (Manufacturer 2), cut from a 5-inch-OD drill pipe were evaluated through laboratory tests. The evaluation parameters included resistances of both coatings to torsion, flattening, abrasion, and tension, and resistance of TC2000B TM to corrosion in high temperature and pressure brines that: (1) have a high ph, (2) contain CO 2, or (3) contain CO 2 and H 2 S. OBJECTIVES The objectives of the tests are to evaluate the coating resistance to torsion, flattening and abrasion, coating flexibility and adhesion, and anti-h 2 S and anti-co 2 capacity. The evaluation is a first step to understand the coating behavior if it were used in service conditions under well such as ph=12.5, temperatures below 150 ºC and pressures less than 1,000 psi. Mechanical Tests EXPERIMENTAL TESTS For these tests, duplicate samples were used for TC2000. Only a single set of samples was used for TC2000B. Specimens: The test specimens were provided by clients as shown in Figure 1. They were labeled for designated mechanical tests. For torsion testing, the nine front-right strip samples, nominally 200-mm long and 25-mm wide, were used. They were photographed prior to testing for comparison with them after the test. For flattening testing, the three back-left samples were used. They were nominally a circumferential quarter section of the pipe, approximately 110-mm in length. Photographs were captured prior to testing for comparison with specimens after test. For abrasion testing, the three back-right ring samples, full diameter sections of the pipe, nominally 120-mm long, were used. Prior to testing, the sections of the pipe were cut into three equal circumferential segments; one segment from each sample was used for testing. Prior to testing, the coated surface was photo-documented for post-test comparison. For tension testing, the three front-left longitudinal strips, nominally 185-mm long and 30-mm wide, were used. Prior to testing, a 20-mm wide and 50-mm long gage section was machined into the specimen. Prior to machining and testing, each sample was photographed for post-test evaluation of the coating. Test Procedure: For all mechanical tests performed, the temperature and humidity were nominally C and 20-30%, respectively. 2 2

3 The torsional testing was conducted following the amount of rotation for each sample shown in Table 1. The testing was performed on a torsional test frame made by MTS Systems Corporations. Hydraulic test fixtures were used to secure the samples during loading. After each test, photographs were taken to document the conditions of the pipe and coating. For flattening test, a 100-kip MTS servohydraulic test frame was used to provide compressive loading required to flatten the test samples. Two parallel hardened steel loading platens (300-mm diameter) were used during testing without lubrication on the contact surfaces. The constant displacement rate was set to be 12-mm/min. Testing was terminated when the mid-section of the inside surface made contact with the opposing platen resulting in a flat specimen. After testing, the samples were examined and photo-documented to investigate the coating integrity. The abrasion resistance characterization for the coatings was performed in accordance with the client-supplied documentation and ASTM D968 [1]. The procedures and requirements provided by the customer were in agreement with the ASTM standard. An HP-1160 Gardner Falling Sand Abrasion Tester was used for the abrasion testing of coated pipe samples (Figure 2). The test procedure follows ASTM D968, ASTM D333 [2], D1395 [3], and D2205 [4]. The media used for the testing was Ottawa, Illinois natural silica sand and is specifically required by ASTM D968. The sand was graded and filtered through a No. 20 (850 μm) sieve to meet the requirements of the standard. Prior to testing, the sand abrasion tester was calibrated to the set sand flow rate per the required 0.1 L/s. A practice sample was used to ensure the abrasion pattern to be consistent to that required by ASTM D968. Given the size of the test funnel, only 4-L of sand could be used per pass. Once the funnel was empty, another 4-L of sand was added to the funnel and the flow baffle removed to initiate flow. This process was repeated and the volume of sand used to achieve a 4-mm diameter wear pattern was recorded. Pictures were taken during the process to document the progressive wear of the coating. For tension test, tensile samples were loaded with the above 100-kip MTS servohydraulic test frame. In order to secure the specimen during loading, 100-kip hydraulic wedge grips were used that mechanically clamp the grip ends of the test sample. The objective of the tension testing was to load the sample to the 0.2% offset yield stress and then examine the coating for delamination, cracking, or any other signs of degradation. Strain gages were adhesively bonded to the machined surfaces (sides) of each sample to monitor the applied stress/strain and used to determine when the yield stress had been achieved. The samples were not tested to failure. Environmental Tests Per client s request, the environmental tests were conducted only for TC2000B TM. Specimens: The coating specimens were originally provided by the client as full diameter sections of pipe, nominally 120-mm long (see Figure 1). For this coating test, each ring specimen was sectioned into six even samples. With a total of three ring specimens, eighteen test samples were prepared. One ring specimen corresponded to one environmental test. All samples were slightly polished and coated with epoxy resin except the inner coating surface. After the metal-epoxy bonding was established, by visual examination the best three of the six samples were cut from one specimen and selected for testing. A total of three tests were conducted. 3 3

4 Test Procedure: The following test procedure was developed to meet the requirements of the clients. Test 1: In N2 + H2O Environment: Three selected identical samples, cut from a ring specimen, were electrically insulated from each other and then, immersed into a test solution of ph=12.5 in an autoclave. Pure N2 was purged to deaerate the solution overnight before the autoclave was sealed and the solution temperature and pressure were raised to 148 C and 1050 psi, respectively. The test duration was 16 hours. When the test was finished, the autoclave body was slowly cooled down to 93 C. Correspondingly, the pressure slowly and evenly dropped to normal pressure within minutes. The samples were then taken out, rinsed and visually examined for coating appearance. Adhesive strength inspection was carried out afterwards. Test 2: In CO2 and Formation Water Environment: Three selected identical samples were cut from one ring specimen. They were electrically insulated from each other before being immersed into the test solution in an autoclave. The solution was formation water originated from Tarim Oilfield (Xinjiang Uyghur Autonomous Region, China) and had a chemical composition of: Cl - : g/l, SO 4 2- : 0.26 g/l, HCO 3 - : 0.10 g/l, Mg 2+ : 0.58 g/l, Ca 2+ : 6.81 g/l, Na + + K + : g/l. High purity nitrogen gas was purged overnight to deaerate the solution before test. The autoclave was then sealed and the high pure nitrogen gas was continued to purge for 2 hours to remove oxygen. After heating the solution to the designed temperature of 160 C, the pressure was raised to 508 psi by charging CO2. Maintain the temperature and pressure. At 180 hours after start of testing, take one sample out of the autoclave following cooling of the autoclave. Check if the coating has failed. Resume the high temperature and pressure testing after de-oxygenating. When the test was terminated following another 180 hours of testing, the autoclave was cooled to room temperature and the pressure to normal pressure. Take out the remaining two samples, rinse, and examine them immediately. Test 3: In CO2 + H2S + Formation Water Environment: The procedure of the experiment is the same as used for Test 2. The formation solution was originated from the Chang Qing Oilfield (Qinghai province, China) and had a chemical composition of: NaHCO3: 0.2 g/l, NaSO4: 0.2 g/l, CaCl2: g/l. The test was conducted at a CO2 partial pressure: 508 psi, H2S content: 7000mg, and at a temperature: 160 C. With calculation of CO 2 and H 2 S volume concentrations at room temperature, mixed gas of CO 2 and H 2 S were ordered and used for the test. The test duration was 360 hours. 4 4

5 After 180 hours of testing, one sample was taken out of the autoclave to examine the coating, and then continued the test. When the test was ended, the autoclave body was cooled down to room temperature and normal pressure and the remaining two samples were taken out and rinsed for visual examination. Mechanical Tests RESULTS AND DISCUSSION Torsion test: The photo-documented samples for torsion testing are presented in Figures 3. The before- and after-images are presented for comparative purposes. For coating TC2000B, all samples experienced coating delamination for all levels of rotation tested (Figures 3a.1-3). The severity of delamination increases as the rotation level increases. For coating TC2000, both specimens after rotation of 90 angle was shown to have experienced no coating delamination, while their surface appearance and texture of the coating started to change (Figure 3b.1). For the 180 (Figure 3b.2) and 360 (Figure 3b.3) conditions, all specimens demonstrated coating delamination and separation of the coating from the substrate. Flattening test: The before- and after-conditions of the flattening specimens are presented in Figure 4. For coating TC2000B, all specimens appeared to experience slight delamination and cracking in the longitudinal direction of the pipe section (Figure 4a). The highest density of coating failure occurred along the mid-section of the sample and is presumably due to the high strains in that region during loading. By examining the sample after the testing, it appeared that the coating separated from the primer coat (as can be witnessed in the figure). The primer color was gray. For coating TC2000, the results are the same as TC2000B for both specimens. They experienced slight delamination and cracking in the longitudinal direction of the pipe section; the highest density of coating failure occurred along the mid-section of the sample (Figure 4b). After the testing, the coating was seen to have separated from the primer coat. The primer color for both specimens was dark red. Abrasion resistance test: The results of the abrasion resistance testing are presented in Table 2 for both coatings. The table contains average coating thickness for each sample, total volume of sand used to achieve the 4-mm wear spot, and wear resistance value (volume per thickness) for each sample. Sequential images of each test are provided in Figure 5 to demonstrate the pattern of wear as the quantity of sand used increases. For coating TC2000B, the wear resistance value (volume per thickness) was 2.16 L/μm. As shown in Figure 5a, as the volume of sand used increases, the wear spot slowly increases in size. The first stage of wear is through the paint to the primer coat followed by wear through the primer coat exposing the steel substrate. It is necessary to note that the wear resistance was determined based on testing to the steel substrate, which included abrading through the coating and primer layers. 5 5

6 For coating TC2000, the wear resistance values for the two samples are similar, at 1.63 L/μm and 1.68 L/μm, respectively. The overall wear pattern demonstrated by the two samples tested was consistent (Figure 5b.1-2). Tension test: The after-test images of the tension testing are presented in Figure 6. Note that the coating delamination in the gripping region (each end) of the samples is not a result of the tensile loading but a result of the high clamping force gripping used to secure the specimen during testing. The region of interest is the narrow gage section of each specimen. Some coating separation is noted along the edges of the gage section and that is a result of the machining process, not the tension loading. For coating TC2000B, visual examination of the post-test specimens showed no sign of coating delamination or separation (Figure 6a). The results presented herein only apply loading up to the yield stress of this material and not above the yield stress. For coating TC2000, similar results to that of TC2000B are shown (Figure 6b.1-2). Environmental Tests The environmental tests were conducted for coating TC2000B, with the results shown in Figure 7. Test 1: In N2 + H2O Environment: Figure 7a shows the six samples cut from one ring specimen prior to test. The left three samples were used for testing. After test, the three samples were placed to their original position together with the three samples not tested for comparison. The post-test specimens show that the coating appears intact with slight color change. Under optical microscope at a magnification of 30x, no blister or other types of coating delamination were observed. Test 2: In CO2 and Formation Water Environment: In Figure 7b, the post-test sample placed on the upper-left corner, labeled on the paper by pull, was one that was pulled out after 180 hours of test. After another 180 hours (or a total test of 360 hours), the remaining two samples were pulled out and placed in their original positions together with the three samples not tested. They are labeled by The coating appeared intact with slight color change. Under optical microscope at a magnification of 30x, no blister or other types of delamination of the coating were observed. Test 3: In CO2 + H2S + Formation Water Environment: In Figure 7c, the post-test sample placed on the upper-left corner, labeled on the paper by pull, was one that was pulled out after 180 hours of test. After another 180 hours (or a total test duration of 360 hours), the remaining two samples were pulled out and placed in their original positions together with the three samples not tested. They were labeled by

7 Although the epoxy coating coated prior to testing shown slight delamination near the edges of the samples, the original inner coating appears intact with slight color change. Under optical microscope with a magnification of 30x, no blister or other types of delamination of the coating were observed. CONCLUSIONS For coating TC2000B, under torsional loading and flattening the coating demonstrated degradation in the form of delamination and disbonding. The tensile loading demonstrated no signs of coating failure. The wear pattern for abrasion testing was slightly irregular with a wear resistance of 2.16 L/μm for this particular coating/primer combination. For coating TC2000B, the specimens appeared to be intact after each of three high temperature and high pressure environmental tests. No blister or other coating delamination was observed. For coating TC2000, only mechanical tests were performed. Under torsional loading and flattening, the coating of TC2000 demonstrated delamination and disbonding from the substrate. The tensile loading to yield for coating TC2000 did not show any visible coating degradation. The overall abrasion behavior between two samples tested was consistent, with an average wear resistance of 1.65 L/μm. ACKNOWLEDGEMENTS This work was sponsored by Shanghai Shine Petroleum Pipe Special Coating Material Co., Ltd (Shine), Jiangsu Tube-Cote Shuguang Coating Co., Ltd (manufacturer 1) and Shanghai Tube-Cote Petroleum Pipe Coating Co., Ltd (manufacturer 2). Metcut Research at Cincinnati, Ohio, USA conducted the torsional testing under a subcontract of Southwest Research Institute who provided the samples and a test plan detailing the amount rotation required for each sample. The mechanical tests at SwRI were conducted by staff of the Solid and Fracture Mechanics Laboratory, and the environmental tests by Mr. Steve Clay and Mr. Justin Been. Ms. Lori Salas helped with editing and formatting of this paper. REFERENCES 1. ASTM D968, Standard Test Methods for Abrasion Resistance of Organic Coatings by Falling Abrasive, ASTM, 100 Barr Harbor Drive, West Conshohocken, PA ASTM D333, Standard Guide for Clear and Pigmented Lacquers, ASTM, 100 Barr Harbor Drive, West Conshohocken, PA D1395, ASTM D (1974) Method of Test for Abrasion Resistance of Clear Floor Coatings, ASTM, 100 Barr Harbor Drive, West Conshohocken, PA D2205, Standard Guide for Selection of Tests for Traffic Paints, ASTM, 100 Barr Harbor Drive, West Conshohocken, PA

8 TABLES TABLE 1. SPECIMEN MATRIX FOR MECHANICAL TESTS (TC2000B AND TC2000). Test Type Tension Flattening Torsion Abrasion Resistance Specimen Specimen ID Group Test Condition sample 1 TC2000B sample 2 TC2000 load to yield strength sample 3 TC2000 sample 1 TC2000B flatten coupon between sample 2 TC2000 platens sample 3 TC2000 sample 1 TC2000B 90 sample 2 TC2000B 180 sample 3 TC2000B 360 sample 4 TC sample 5 TC sample 6 TC sample 7 TC sample 8 TC sample 9 TC sample 1 TC2000B sample 2 TC2000 abrade 4-mm spot sample 3 TC2000 TABLE 2. WEAR RESISTANCE FOR THE THREE SAMPLES TESTED (TC2000B AND TC2000). Specimen ID Average Coating Total Volume of Wear Resistance, Thickness, μm Sand, L L/μm AB 1-1 (TC2000B) AB 2-1 (TC2000) AB 3-1 (TC2000)

9 Flatting test specimens Abrasion test specimens Tension test specimens Torsion test specimens Figure 1: Mechanical testing specimens removed from crate. (a) Figure 2: Sand abrasion test: (a) setup, (b) Image of sand falling out of the funnel and striking the test sample. (b) 9 9

10 Before test (a.1) After test Before test (a.2) After test Before test (a.3) After test Before test first sample After test first sample Before test sec (b.1) After test second sample 10 10

11 Before test first sample After test first sample Before test second sample After test second sample (b.2) Before test first sample After test first sample Before test second sample After test second sample (b.3) Figure 3. Torsional test before and after: (a) coating TC2000B TM 1). 90 rotation, 2). 180 rotation, 3). 360 rotation; (b) coating TC2000 TM 1). 90 rotation, 2). 180 rotation, 3). 360 rotation 11 11

12 Before test (a) After test Before test first sample After test first sample Before test second sample (b) After test second sample Figure 4. Flattening test - before and after (a) TC2000B TM and (b) TC2000 TM

13 Before test (1) Test with 400 L (2) Test with 460 L appearance of metal (3) Test with 540 L end of test. (a) Before test (1) Test with 400 L (2) Test with 480 L (3) Test with 500 L end of test (b.1 first sample) 13 13

14 Before test (1) Test with 260 L (2) Test with 380 L (b.2 second sample) (3) Test with 460 L end of test Figure 5. Abrasion test before and after (a) TC2000B TM and (b) TC2000 TM - 1) first sample and 2) second sample. (a) (b.1) Sample 1 (b.2) Sample 2 Figure 6. Tensile test (a) TC2000B TM and (b) TC2000 TM - 1) first sample and 2) second sample

15 Before test The three samples on the left were after test (a) Test 1 N 2 & ph=12.5 Before test (b) Test 2 CO 2 & formation water The three samples on the left were after test Before test The three samples on the left were after test (c) Test 3 CO 2 & H 2 S & formation water Figure 7. TC2000B TM only: six samples were cut evenly from one full circumferential pipe section prior to test and the left tree samples experienced test in brine: (a) with a ph of 12.5, (b) containing CO 2 and (c) containing both CO 2 and H 2 S