Development And Mechanical Properties of X120 Linepipe

To enable the development of remote gas sources, X120-grade UOE linepipe has been developed. Low carbon-low Pcm and Mn-Ni-Mo-Nb-V-B bearing steel with a microstructure of fine ausformed martensite and bainite has excellent combinations of strength and toughness. With respect to longitudinal seam welding, the X120 pipe exhibits good heat-affected-zone (HAZ) cracking resistance due to a low Pcm. Deformation behaviors of the X120 linepipe were investigated using field bending and hydrostatic burst tests. The results verify that the overmatched seam weld in the X120 is sufficient to enable burst strength consistent with this grade of pipe. Sufficient deformability of the X120 for field bending was demonstrated using existing pipeline construction equipment. INTRODUCTION To maximize economic advantages, the use of higher-strength steels (X80 and over) in linepipe systems has been investigated (Sanderson et al., 1999). X80-grade steels have been developed and utilized for gas linepipes. Regarding X100, this steel has been developed, and the characterization of prototype pipes has been extensively studied by pipe manufacturers (Hashimoto et al., 1988; Kawabata, 1995) and by a joint industry project of major oil companies (Hammond and Millwood, 2000). In the case of X120grade steel, ExxonMobil has developed a basic concept for manufacturing and applying the steel to high-pressure gas linepipes. In 1996, ExxonMobil and Sumitomo Metals started a cooperative research and development effort on ultra high-strength linepipe steels (Fairchild et al., 2002). The joint project was initiated to develop and commercialize X120-grade steel by conducting both laboratory tests of candidate plates and full-scale tests of prototype pipes. This paper will discuss the metallurgical concept of X120-grade linepipes, the characteristics of prototype pipes, the deformation behavior during hydrostatic burst tests, and the results of field bending tests. Tables 1 and 2 summarize the target properties established at the beginning of the joint development. Because API5L has not set ∗ISOPE Member. Received August 18, 2003; revised manuscript received by the editors December 19, 2003. The original version (prior to the final revised manuscript) was presented at the ISOPE Symposium on HighPerformance Materials in Offshore Industry, the 13th International Offshore and Polar Engineering Conference (ISOPE-2003), Honolulu, Hawaii, USA, May 25–30, 2003.