Discussion on heating for in-service welding of oil and gas pipelines

In-service welding is a key technical aspect of the maintenance and emergency repair of oil and gas pipelines. During this process, the flow of medium in the pipeline accelerates weld cooling, significantly increasing the risk of hydrogen-induced cracks. Therefore, effective heating is essential for ensuring weld quality. This paper systematically discusses heating-related issues for in-service welding, focusing on the advantages and disadvantages of three techniques: flame heating, electrical heating, and induction heating, along with their respective application scenarios. Additionally, conbined natianal and foreign standards with practical experience, optimization suggestions for heating under different conditions are proposed. The study results indicate that induction heating is particularly advantageous in harsh conditions, such as high heat conduction rates or elevated flow rates of the medium. Proper control of postheating temperature and time can effectively mitigate the risk of hydrogen-induced cracking. For Type B sleeve welding onto high-grade steel pipelines, it is crucial to carefully consider both the preheating temperature and the softening of the heat-affected zone to prevent a decrease in pipe strength due to excessive heating. Based on practical engineering cases in China, this paper offers suggestions for improving the heating process in in-service welding, aiming to provide a technical reference to ensure pipeline safety during maintenance.