Welding of 15NiCuMoNb5-6-4 and austenitic stainless steel thickness pipes is necessary in the primary loop pipes installation for the platform. In the process of formulating welding procedure specification of the pipeline pre-welding between 15NiCuMoNb5-6-4 and Z3CN20-09M, some macroscopical cracks appeared repeatedly on the surface of bend-test specimens, while other performances of welding joints such as mechanical properties at room temperature, high temperature tensile properties and impact properties could meet the relevant codes requirements. Focus on present problem, chemical composition analyses, metallographic microstructures analyses and scanning electron microscope observation were adopted to find the welding failure root cause. Finally, INCONEL®152M and 52M with 30% chromium were chosen to be the welding materials because of good ductility dip cracking resistance. It was found that the performance of the welding joints could satisfy the codes and engineering requirements.

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