Resurface corroded flange gasket seating face 2

[jtseng123]

All,
Our field reported the 18"-150#, SA-105 flange, the 1/16" high of raised face is corroded and only 0.5 mm left in some area. Please see the photo. I plan to resurface to remove the raised face and make it a flat face. Doing that it becomes not standard B16.5 flange due to 1/16" less in thickness.
However, I ran App 2, and it passed if not considering additional 1/8" corrosion allowance in the flange thickness, and only 200 psi overstresed in seating condition if considering additional 1/8" corrosion allowance in the thickness.
Any problem of resurfacing ?

 

[SnTMan]

jtseng123, you may make a flat-face by removing the raised face with no further justification, provided the thickness tf is maintained, see para 6.3.2 and Table 8 / F8 note 3.

Is it feasible to weld repair and reface? Refacing services are common.

Regards,

Mike

 

[fegenbush]

I agree with Mike that refacing of flanges is quite common. However, if you are going to do this, I recommend taking at least a skim cut on the old face to remove any impurities before adding weld overlay. This minimizes the opportunity for pinholes in the weld overlay.

 

[racookpe1978]

Remember, if yo have a RF flange on side 1, you should have a RF flange on side 2 (the piping side) of the flanged joint.

A 2-sided FF flange will have lower pressure on the gasket (because the area of the full gasket is pressed by the two flanges' raised faces) so a FF-FF gasket will require a different torque spec. A FF-RF gasket connection will press the gasket from only "half" the side of the gasket where the RF side is, and is discouraged (prohibited ?) for dangerous fluids.

As noted above, companies offer re-facing services, but these are expensive.

Have you considered half-cutting down the 1/16 high flange RF so that the amount of the RF surface is increased, but re-welding (weld buildup) is not needed? Even the remaining 1/32 inch RF will concentrated pressure as originally intended. The impact of a 1/32 shortening of the pipe section can be reasonably ignored. An RF flange with only "pinhole" areas of non-contact on the face can still serve. A RF raised face with scratch (grooves!) across the entire RF MUST be replaced or repaired "in toto".

 

[jtseng123]

racookpe,
I am not quite understanding your point about the FF-RF or FF-FF. Can you not use spiral wound gasket which has inner/outer rings in FF-FF or FF-RF joint ? What is the technical reason ?

We will not use full face gasket even it will be machined down to full face.

 

[fegenbush]

jtseng123,

"if yo have a RF flange on side 1, you should have a RF flange on side 2"

It is perfectly acceptable to mate a RF to a FF flange, but the gasket seating width is different. Thus, the comment about adjusting torque specifications accordingly. The comment from racookepe1978 is just best practice.

For determination of the gasket seating width in different scenarios, please see Table 2-5.2 of ASME Section VIII Div 1.

 

[jtseng123]

The scenario I have is (1b). I do not see how the width will be different.

 

[jtseng123]

Is "R" stamp required for flange replair by skimming out deeper than the existing raised face to remove all corrosions, then do weld oveylay to build-up the gasket seating face, and then machining ?

 

[fegenbush]

It would be considered a repair and require an R stamp. Reference NBIC Part 3 Paragraph 3.3.3.n.

 

[metengr]

Yes, a repair organization must have a valid R-Certificate to weld restore the flange sealing surface or pressure boundary of the flange.

 

[jtseng123]

Will do. Thanks all.