Effect of Strength Mismatch of Girth Weld on Safety of the West-East Pipeline

The West-East Pipeline is the first of high-pressure, high-grade steel (X70) and large diameter (Φ1016mm) gas transmission pipeline in China. Evidently, Safety of the Pipeline is the most important case that the gas company have to take care of. Previous study showed that strength mismatch of girth weld had great effect on the integrity of the pipeline. Overmatch is preferred for low-grade pipeline (steel grade is usually X60 or lower). As to the high-grade pipeline, in order to reduce the sensitivity of cold crack, hydrogen induced crack (HIC) and stress induced corrosion crack (SCC), etc., under-matched girth weld is recommended somewhere. In this paper, based on a lot of mechanical test results, the effect of different mismatched girth weld on property of the West-East Pipeline is analyzed. The study indicated that mismatch of girth weld has effect on property of the Pipeline, such as limit load, fracture toughness and threshold defect sizes, etc. According to the research results, some advices are presented for design, maintenance and repair of the Pipeline.