Weld Overlay on Flange Faces
Weld Overlay on Flange Faces
(OP)
Are there any hard and fast rules as to the extent of corrosion resistant alloy weld overlay required on subsea flange faces? I am in a debate about whether only the ring groove should be overlaid or if overlay of the full flange face is required. The overlay alloy would be Alloy 625.
The question applies to ANSI or API flanges - but I am specifically concerned with API 6A flanges.
The question applies to ANSI or API flanges - but I am specifically concerned with API 6A flanges.





RE: Weld Overlay on Flange Faces
It is fully dependent on your corrosion requirements, ie. if the mating pipe is CRA pipe then obviously the flange wet surface will also be CRA overlayed which includes the flange full face.
Else the flange bore will take care of the wall thickness corrosion allowance similar to the mating pipe and only the groove will be CRA weld overlayed. The gasket shall be inconel. Care is be taken to specify the hardness of the gasket to be less than the groove weld overlay.
When the weld overlay is only on the groove, it normally extends only sufficient to cover the groove and its stressed area. The flange full face need not be overlayed. The argument araises regarding the overlay over the full face when the overlay detail does not provide enough corrosion initiation protection.
For small size flanges it is preferable to weld overlay the full face to avoid corrosion initiation at the weld overlay/flange interface.
The weld overlay generally used is SS316 or Inconel 825. Inconel 625 is costlier and more superior and generally used for pipe CRA cladding than overlay.
Narendranath R
narenr@narendranath.itgo.com
http://www.narendranath.itgo.com
Pipeline engineering is made easy with state of the art computer software, visit www.narendranath.itgo.com.
RE: Weld Overlay on Flange Faces
RE: Weld Overlay on Flange Faces
For info - its Incoloy 825 and Inconel 625...slightly different alloys. Incoloy 825 has higher Fe and is stabilized with Ti. Inconel 625 is NiCrMo alloy stabilized with Nb. Incoloy 825 is softer and is typically what we specify for gaskets against the Inconel 625 overlay.