Welding L415/316L Bimetal Composite Pipe Using Post-Internal-Welding Process

The butt welding of bimetal composite pipes generally adopts single-side welding, which easily gives rise to the problems such as high cost or crack initiation. In this paper, the butt welding of L415/316L bimetal mechanical lined pipes was conducted using post-internal-welding process, which is double-side welding process, proposed by the authors. Firstly, the effect of groove shape on the weld process was discussed. Then, microstructures and mechanical and corrosion-resistance properties of welded joints welded using two different welding materials, 309MoL and 309L, were investigated. The results show that the most suitable groove is that L415 is V shape with angle of 60 degrees and blunt edge of 1 mm and 316L is stripped 6-8 mm. The weld of both 309MoL and 309L is composed of austenite and a small amount of ferrite, but the presence of Mo can refine the grains and increase the content of ferrite phase. The width of transition layer is about 0.6-0.8 mm located at the weld junction of stainless steel weld and carbon steel weld, and the transition layer mainly contains martensite. The tensile and bending performances of the welded joints using both 309MoL and 309L do meet the standard requirements. The welding wire 309MoL can improve the corrosion resistance to Cl- compared to 309L. It is advisable to use the post-internal-welding process and 309MoL for the welding of bimetal composite pipes under environments containing Cl-.