Welding over thermal spray coating
Welding over thermal spray coating
(OP)
Does anyone have experience welding over a thermal spray coating placed by HVOF (high-velocity oxy fuel) process? I need to do a weld metal build-up repair on 2-1/4 Chrome (SA387-F22) base metal that has been overlayed with 347 stainless. The weld metal build up will also be of 347 SS. I'm wondering what effect welding will have on the sprayed overlay. Will there be any lack of adhesion at the HAZ, or will the sprayed metal simply fuse like a weld metal overlay?





RE: Welding over thermal spray coating
No. Having dealt with weld overlays and HVOF coatings on boiler tubing I would not risk trying to weld over the existing HVOF coating. The deposited weld metal chemistry will be altered and could adversly affect the performance of the weld overlay in elevated temperature service. If you are going to make a local repair to the base metal - remove the coating, weld restore the FP22 and re-apply the HVOF coating or take the coating off completely and weld repair with the 347 stainless overlay on the base metal. Just wondering- why you have a need for weld repairing the base metal?
RE: Welding over thermal spray coating
RE: Welding over thermal spray coating
Based on your follow-up, I would NOT attempt local repair of the stainless overlay cracks with HVOF given your service conditions. Are you sure the cracks do not extend or have changed direction/orientation into the base metal? Have you excavated the cracks to confirm depth?
RE: Welding over thermal spray coating
RE: Welding over thermal spray coating
RE: Welding over thermal spray coating
RE: Welding over thermal spray coating
If hydrogen is generated or used as part of your chemical process reaction, I would attempt to qualify the "temper bead" welding procedure using hardness testing/metallogrpahic examination of the HAZ in addition to standard bend and tensile testing.