Status and trend of girth welding procedure and joint strength design for bimetallic composite pipes

In this paper, the typical welding procedures of bimetallic composite pipes were introduced, the technical advantages of pipe-end seal welding and butt welding were described and the application cases and failure cases were illustrated. It is indicated that the quality weakness of these weld procedures is seal welding and transfer welding. Then, the research status, prospect and cases of pipe-end surfacing and butt welding technologies were investigated. It is shown that the defect and stress induced by seal welding and transfer welding can be avoided if the rooting, filling and capping are connected with the same alloy welding material. This procedure has been successfully applied in the welding of bimetallic composite pipes for submarine natural gas development. It is the significant development trend and direction of pipe end processing and butt welding of bimetallic composite pipes in the future. Finally, the research status and prospect of strength matching design and defect tolerance design on girth welding joint of bimetallic composite pipes were analyzed. It is indicated that there is no unified welding joint strength design and defects tolerance design theories. And in the future, the related studies shall focus on on-line inspection, corrosion assessment, life estimation and pipeline repair of bimetallic composite pipeline systems.