Development of high-strength heavy-wall seamless line pipe for deep water applications

High-strength heavy-wall sour-service seamless line pipe suitable for deep water applications has been developed by Sumitomo Metal Industries, Ltd. This paper describes the development of these pipes applying inline heat treatment technology, installed in a newly constructed, mediumsize seamless mill. Increasing hardenability through inline heat treatment achieved higher strength (X70) for heavy wall pipe (40mm) even though the carbon equivalent was lower than in a conventional Q&T process. Good toughness was obtained by the control of microalloying elements and impurities such as titanium and sulfur respectively. The pipe produced passed the hydrogen-induced cracking (HIC) test conducted according to NACE TM 0284 solution A. Controlling the microstructure and reducing maximum hardness, utilizing the uniform quenching facility during inline heat treatment, contributed to the test result. Satisfactory data on weldability for practical use were also obtained. (AU)