Separation occurring during the drop weight tear test of thick-walled X80 pipeline steels

Abstract

A separation phenomenon occurring during the drop weight tear test of commercial thick-walled API (American Petroleum Institute) X80 strip steel was investigated in this work. Microstructural analysis showed that the band structure of bainite elongated along the rolling direction works as the initiation sites of separation. The propagation of separation can be promoted not only by the occurrence of the band structure of martensite/austenite constituent, prior austenite grain boundaries, and elongated bainite, but also by fine acicular ferrite and bainite. Wide separation formed in the former case, while the narrow one appeared in the latter case. Some methods were proposed to obtain fine and homogeneous acicular ferrite in thick-walled X80 pipeline steel in order to minimize the occurrence of separation.

Keywords

pipeline steel / drop weight tear test / separation / cracking / band structure

References

[1] Jia YZ, Wang JQ, Han EH, Ke W. Stress corrosion cracking of X80 pipeline steel in near-neutral pH environment under constant load tests with and without preload. J. Mater. Sci. Technol., 2011, 27(11): 1039.

[2] Zok F, Embury JD. On the analysis of delamination fractures in high-strength steels. Metall. Trans. A, 1990, 21(9): 2565.

[3] Shin SY, Hong S, Bae JH, Kim K, Lee S. Separation phenomenon occurring during the Charpy impact test of API X80 pipeline steels. Metall. Mater. Trans. A, 2009, 40(10): 2333.

[4] Hwang B, Kim YG, Lee S, Kim NJ, Yoo JY. Effects of microstructure on inverse fracture occurring during drop-weight tear testing of high-toughness X70 pipeline steels. Metall. Mater. Trans. A, 2005, 36(2): 371.

[5] Tamura I, Sekine H, Tanaka T, Ouchi C. Thermomechanical Process of High-strength Low-alloy Steels, 1988, London, Butterworth & Co., Ltd., 80.

[6] Bramfitt BL, Marder AR. A study of the delamination behavior of a very low-carbon steel. Metall. Trans. A, 1977, 8(8): 1263.

[7] Li Y, Meng L, Lin GF, Han XL, Huo CY, Zhu LX, Feng YR. EBSD analysis of fracture separation in X80 line pipe steel. Proceedings of ASME 2008 Pressure Vessels and Piping Conference, 2008 157.

[8] Li Y, Han XL, Ji LK, Feng YR, Huo CY. Effect of micro-texture on fracture separation in X80 line pipe steel. Proceedings of 7th ASME International Pipeline Conference, 2008 139.

[9] Shin SY, Hwang B, Lee S, Kang KB. Effects of notch shape and specimen thickness on drop-weight tear test properties of API X70 and X80 line-pipe steels. Metall. Mater. Trans. A, 2007, 38(3): 537.

[10] Hong S, Shin SY, Lee S, Kim NJ. Effects of specimen thickness and notch shape on fracture modes in the drop weight tear test of API X70 and X80 linepipe steels. Metall. Mater. Trans. A, 2011, 42(9): 2619.

[11] Shin SY, Hwang B, Kim S, Lee S. Fracture toughness analysis in transition temperature region of API X70 pipeline steels. Mater. Sci. Eng. A, 2006, 429, 196.

[12] Krauss G. Solidification, segregation, and banding in carbon and alloy steels. Metall. Mater. Trans. B, 2003, 34(6): 781.

[13] Matsuda S, Kawashima Y, Sekiguchi S, Okamoto M. Mechanism of separation of a low-carbon low alloy steel control-rolled in austenite and ferrite two phase regions. Tetsu-To-Hagane, 1982, 68(3): 435.

[14] Hwang B, Lee S, Kim YM, Kim NJ, Yoo JY. Correlation of rolling condition, microstructure, and low-temperature toughness of X70 pipeline steels. Metall. Mater. Trans. A, 2005, 36(7): 1793.

[15] Wang SC, Yang JR. Effects of chemical composition, rolling and cooling conditions on the amount of martensite/austenite (M/A) constituent formation in low carbon bainitic steels. Mater. Sci. Eng. A, 1992, 154, 43.

[16] Zhou M W, Yu H. Effects of precipitates and inclusions on the fracture toughness of hot rolling X70 pipeline steel plates. Int. J. Miner. Metall. Mater., 2012, 19(9): 805.

[17] Zhao AM, Wang Y, Chen YL, Tang D, Gao XT, Zuo BQ. Precipitation behaviors of X80 acicular ferrite pipeline steel. Int. J. Miner. Metall. Mater., 2011, 18(3): 309.

[18] Schambron T, Phillips AW, O’brien DM, Burg J, Pereloma E, Killmore C, Williams J. Thermomechanical processing of pipeline steels with a reduced Mn content. ISIJ Int., 2009, 49(2): 284.

[19] Nayak SS, Misra RDK, Hartmann J, Siciliano F, Gray J M. Microstructure and properties of low manganese and niobium containing HIC pipeline steel. Mater. Sci. Eng. A, 2008, 494, 456.

[20] Buzzichelli G, Anelli E. Present status and perspectives of European research in the field of advanced structural steels. ISIJ Int., 2002, 42(12): 1354.

[21] Fujishiro T, Hara T, Sakamoto S, Asahi H, Terada Y. Application of B-added low carbon bainite steels to heavier wall X80 UOE line pipes. Proceedings of 19th International Offshore and Polar Engineering Conference, 2009 80.