Failure analysis of weld cracking of gas gathering pipeline in dewatering station

Abstract

There are a lot of welded joints in the shale gas collection pipeline, so the failure risk of the shale gas production line is very high. A leak has occurred in the gas collection pipeline of a dewatering station, and in order to find out the causes of failure and provide technical support for safe shale gas transmission, macroscopic analysis, non-destructive testing (X-ray flaw detection), mechanical properties, and metallurgical analysis were performed on the failed pipe section, and CFD method was used to further analyze the failure mechanism of the ring weld pipe. The macroscopic analysis yielded the weld height is significantly greater than the standard minimum requirement. Non-destructive testing showed a large number of cracks with varying degrees of extension along the weld circumference on the inner surface of the weld. The chemical composition and mechanical properties of the pipe and the weld met the requirements. The microstructure of the base metal met the standard. There are no inclusions, holes, unfused areas, or other welding defects in the weld zone. The cracks originate from the weld fusion zone, and there are a large number of intergranular microcracks. CFD simulation results show that although the stress concentration caused by the height of the weld does not directly lead to weld cracking, under the influence of the stress concentration, cracks tend to sprout at the coarse grain organization of the fusion zone on the inner surface of the weld and can easily propagate throughout the weld and pipe wall thickness, leading to crack damage. Several suggestions to prevent such a failure were proposed to avoid the occurrence of similar accidents.