Materials Performance

SEP 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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43 MATERIALS PERFORMANCE: VOL. 57, NO. 9 SEPTEMBER 2018 nection produced at the mill is related to the dif ference between torque used to make up connections at the mill and in the field. It is known that the minimum torque used to create a coupling at the mill was 8.2% higher than what was used to make a coupling in the field. The optimum torque to create a coupling at the mill is 3.7% higher than that for a coupling made in the field. The stress at the pin thread vanish point for the premium connections was, therefore, a high-stress location. The total stress borne on the tubing joint i s a c ombination of inst al l ation stresses and stresses applied during opera- tion. So, the greater the connection's make- up torque, the more severe the as-installed interference of the box and pin, which leads to more residual stress after assembly, and then more tensile stress borne by the tub- ing joint. It was shown that tubing trans- verse fractures or cracks at the pin's vanish point for connections produced at the mill were related to its use of higher torque. Temperature Effect on Tubing Failure For this well, the temperature ranged from 41.75 to 43.59 °C at the wellhead. The temperature was 171 °C at a depth of 6,794 m, where gas is stored. In accordance with the temperature gradient determined by Equation (1): (171 – 43.59)/6,793.5 = 0.018755 (1) The temperature ranged from 104.5 to 132.1 °C at depths from 4,146 to 4,712 m where the tubing fractured and cracked. The temperature was 127 °C at a depth of 4,429 m, which is the midpoint of the fail- ure depth range. It should be noted that S13Cr-110 is most sensitive to SCC at tem- peratures from ~105 to 132 °C. Conclusions • The tubing failure mechanism was SCC and corrosion fatigue. • The temperature was 105 to 132 °C at depths of 4,146 to 4,712 m where the tubing broke and cracked. S13Cr-110 is most sensitive to SCC at tempera- tures between 105 and 132 °C. • The failure load borne by the tubing string mainly resulted from bending FIGURE 6 The diagrams show deformation of tubing string under different loads. due to expansion with heat and con- traction with cold. • Ten lengths of tubing transverse frac- tured or cracked at the pin's vanish point of connections made by the mill , which was related to higher make-up torque being used at the mill than in the field. References 1 Y. Ding, et al., "Cause Analysis on Washing out of ⌀88.9mm×6.45mm S13Cr-110 Tubing," J. Physical Testing and Chemical Analysis Part A: Physical Testing 10 (2011): pp. 663-667. 2 S.L. Lv, et al., "Analysis on Causes of a Well Casing Coupling Crack," MP 51, 4 (2012): pp. 58-62. 3 S.L. Lv, et al., "Cause Analysis on Tubing Cor- rosion in Well YH 301," J., Corrosion & Protect. 29, 11 (2008): pp. 706-709. 4 S.L. Lv, et al., "Analysis of Premium Connec- tion Downhole Tubing Corrosion," MP 47, 5 (2008): pp. 66-69. 5 API SPEC 5B, "Threading, Gauging, and In- spection of Casing, Tubing, and Line Pipe Threads" (Washington, DC: API, 2017). 6 P.B. Yuan, S.W. Guo, and S.L. Lv, "Failure Analysis of High-Alloy Oil Well Tubing Cou- pling," MP 49, 8 (2010): pp. 68-71. 7 S.L. Lv, et al., "Analysis of N80 BTC Downhole Tubing Corrosion," MP 43, 10 (2004): pp. 35-38. XIANG-TONG YANG is a senior engineer with Tarim Oil Field, Xinjiang, China. He has 14 years of experience on aspects of well logging and test oil engineering. He graduated from the Oil Field Physical Geography Specialty of China University in 1996. JUN-FENG XIE is a senior engineer with Tarim Oil Field. A graduate from Tsinghua University, he specializes in protecting OCTG and oil equipment from corrosion. HUA WANG is a senior engineer with Tarim Oil Field. A graduate from the Jianghan Petroleum Institute, he specializes in fail- ure analysis for oil country tubular goods (OCTG) and oil equipment. MI-FENG ZHAO is a senior engineer with Tarim Oil Field. A graduate from Jilin Uni- versity, she specializes in failure analysis of OCTG and oil equipment. YAN LI is assistant engineer with Tarim Oil Field. A 2012 graduate from Northeast Petroleum University, she specializes in failure analysis of OCTG. LEI MA is engaged in the failure analysis of OCTG and equipment in Tarim Oil Field. He graduated from China University of Petroleum (Beijing) in 2012 with a master's degree. Continued on page 44 Fracture Investigation of a S13Cr-110 Tubing String with Premium Joints

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