Current status of welding and weld testing technologies for large-diameter high-grade pipelines in China

In China, semi-automatic welding technology is commonly used at large-diameter high-grade pipelines, and the issues related to its welding quality emerge gradually. To solve these problems, the welding technologies and the weld testing technology for large-diameter high-grade pipelines were explored. First, the effects of semi-automatic welding and automatic welding on the girth weld quality of large-diameter high-grade pipelines were investigated. And the factors affecting the welding quality were verified based on the failure analysis report of high-grade pipeline joint leakage in West-to-East Gas Pipeline Project, the low-temperature impact test & metallographic examination report of tabular goods and the girth welding test. Second, semi-automatic welding and automatic welding were economically compared, and the relationship between the cost and the fulfilled work load of welding outfit was clarified. Third, the reliability of automatic ultrasonic testing technology was studied and the automatic weld testing method suitable for domestic conditions was proposed. It is indicated that as for large-diameter high-grade pipelines, automatic welding can avoid effectively the low and discrete low-temperature impact energy of semi-automatic girth weld, and it is advantageous with reliable quality and efficiency improvement. However, the automatic welding is economically superior to the semi-automatic welding so long as its work load is higher than the economic value. The weld quality of automatic welding can be inspected by the automatic ultrasonic testing technology. To sum up, it is recommended to implement fully the automatic welding technology in the construction of large-diameter high-grade pipelines.