Improving groove forms of girth welds of unequal wall thickness in oil and gas pipelines

In recent years, several failure accidents of girth welds occurred in oil and gas pipelines in China, drawing increasing attention from domestic and foreign pipeline industries. Herein, the cases of girth weld failure of oil and gas pipelines were summarized and analyzed. On this basis, the causes for the failure of girth welds with unequal wall thickness, taking a larger proportion in the failure accidents, were analyzed, and suggestions were put forward for the counterbore-tapered grooves of girth welds with unequal wall thickness. Under the background of a natural gas pipeline with a diameter of 1 422 mm in the Fourth Line of the West-to-East Gas Pipeline(Turpan-Zhongwei), the counterbore-tapered groove scheme of girth welds with unequal wall thickness was designed for the joining of straight pipelines with the hot-bending bends based on the 5 principles of welding, nondestructive testing, groove processing, internal inspection, and stress concentration. Meanwhile, the strength of grooves was analyzed comparatively. The research results could provide a reference for improving the welding quality of girth welds with unequal wall thickness and the intrinsic safety of pipelines.