Lined Stainless Steel Composite Pipe Welding Failure Research

In order to study the weld cracks occurred in the L415QB inner liner stainless steel clad pipes, the conventional methods of failure analysis, including optical microscope, microhardness tester, and scanning electron microscope, EDS were adopted to the failure analysis, furthermore, contrast test was also set. The conclusions are shown as follows:(1)The difference of properties between the base metal and composite metal lead to different stress on both side of weld joints, which easily resulted in stress concentration; Also, the chemical diffusion and migration among the base metal, composite metal and weld bead lead to brittle phases, combined with the stress concentration, the cracks produced.(2) The slag inclusions produced in the weld beads also lead to stress and strain concentration and thus the cracks occurred. For tensile stress between the weld metal and the slag inclusion contraction separated the weld metal and inclusions, then the weld cold cracks occurred.(3) In order to prevent the cracks in weld metal, some useful ways, such as reasonable groove design, control in interpass temperature, low current welding and full clean of the weld beads can be used to avoid the formation of stress concentration and brittle phases, which can effectively prevent the weld cracks.