Crevice corrosion properties of weld overlays of Ni-based alloys compared to 6Mo stainless steels for seawater applications

The corrosion properties of weld overlays of Ni-based alloys have been investigated using different test methods. Of the different weld overlays tested, only the alloy 59 types seems to be beneficial with respect to crevice corrosion initiation compared with 6Mo base material. Both alloy C-22 and alloy C-276 weld overlays have slightly lower critical crevice temperatures (CCT`s) while alloy 625 and C-4 weld overlays have considerably lower CCT`s than the 6Mo base material. Applying a test method or using a gasket material giving less critical crevice geometry than PTFE does, the critical crevice corrosion temperature increases considerably. Care must be taken when evaluating results from testing and when specifying test temperature and test method for quality control. A crevice corrosion test method simulating the condition when starting up a chlorinated seawater system has been developed.