Qualification of Local Stress Relief Heat Treatment of Double Submerged-Arc Welded DSAW Pipe for Reel-Lay Installation

Reel-lay installation is one of the most effective methods for subsea pipeline installation. Pipes subject to reeling installation experience cyclic plastic deformations and tight control of the yield strength range, yield strength to ultimate tensile strength ratio (YS/UTS) and uniform elongation values is required on the delivered pipe. Double Submerged-Arc Weld (DSAW) pipes formed from Thermo-Mechanically Controlled Process (TMCP) plates do not normally exhibit the minimum requirements for plastic strain requirements such as minimum YS/UTS ratio or uniform elongation values. This paper describes a process for increasing the reelability of DSAW pipes. This has been achieved by induction heating of DSAW pipe ends to normalise the mechanical properties at pipe joints. The mechanical properties of the treated section have been measured and verified against design rules for reeling, based on industry standards such as DNVGL-ST-F101 [Ref. 1] and TechnipFMC supplementary requirements. The improvement in mechanical properties is measured by comparison with the as-manufactured properties of adjacent sections. A commercial study demonstrates that the locally heat-treated DSAW pipe is a cost-effective alternative to seamless pipes for reel-lay installation.