Weld Overlay on Flange Faces

[tbarnett]

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.

 

[narenr]

There are no rules as to govern the extent of the CRA overlay on the flange face.

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

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[Hush]

Assuming your retained fluid is non-corrosive, normally only the ring groove is overlaid, 1/8" minimum with a class Fe5 625, to protect the sealing surface. Minor or mild pitting on the flange face is not detrimental to strength and at any rate is protected by your marine coating. Its been my experience that most end users will use a 316 or Monel ring gasket with a CRA ring groove.

 

[tbarnett]

Thank-you very much - that really helps me!

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.