Key factors for safety improvement design of girth weld in high-grade large diameter natural gas pipelines

Failure of girth welds in high-grade steel pipelines is common. With the surge in mileages of high-grade steel pipeline, the failure of girth weld in high-grade steel pipelines has drawn an increasing attention from domestic and foreign pipeline industries. The typical cases in China and abroad were classified and analyzed. Based on the fracture mechanics theory of girth weld fracture failure, the failure causes were analyzed for the key links that affect the safety of girth weld, and the safety improvement measures were hereby proposed, involving the pipeline welding technology, steel control, welding materials, strength matching of welded joints, internal groove types for unequal wall thickness, nondestructive testing, intelligent inspection, stress and strain, construction management, etc. These measures have been widely applied to the China-Russia Eastern Gas Pipeline Project, and are planned to be used in the middle section of the Line 3 and the Line 4 of West-to-East Gas Pipeline Projects which are to be built. Their practices are anticipated to provide support for improving the service reliability of girth weld in high-grade steel pipelines.