Metallurgical reactions in welding of clad X60/X65 pipelines

This work investigates the metallurgical changes occurring during welding of clad pipes. Welded samples with and without a Ni-interlayer between the clad and base metal (BM) were investigated by light optical microscope, electron microprobe analysis and microhardness measurements. The investigations have focused on the microstructure and properties of the clad and BM close to the weld, in addition to the root and hotpass. The results indicate that the presence of a Niinterlayer prevents carbon diffusion across the BM-clad interface during exposure to elevated temperatures, thus preventing the formation of a hard and crack susceptible microstructure.