Study On Welding Procedure And Mechanical Properties Of The X65 Steel Catenary Riser Girth Joints By Narrow-gap TIG Welding

With the depletion of the land and offshore oil and gas resources,the steel catenary riser has been favored by various countries for its unique advantages in the development of deep-water and ultra-deep-water resources.The research on deep-water oil and gas exploitation was carried lately in China,so a high-quality welding technology was urged to develop to ensure the good comprehensive performance of the steel catenary riser joints,especially the fatigue performance.The main factors and matters needing attention were studied in the process of backing,filling,and capping welding to obtain the appropriate parameters.Then,the effect of misalignment and assembly gap on backing welding procedure,so as to provide the error range of misalignment and assembly gap.Then,the mechanical propertied of the full position and horizontal position welding joints were carried and analyzed.The results showed that the conventional mechanical propertied and fracture toughness of narrow gap TIG welding joints are excellent and the fatigue data is upon the F3 curve of the DNV-RP-C203 standards at the typical stress range.Besides,the misalignment mode has a significant influence on the fatigue cracking initiation position of horizontal welding joints.The fatigue crack of upper-misalignment-joint is almost from the upper side of the root toe,and the fatigue crack of joints without misalignment is mainly from the bottom of the root toe,and the fatigue crack of down-misalignment-joint is all from the bottom of the root toe.