Damaged flange facing - should this get repaired or replaced

[JG MechEng]

Situation:

4" 1500# equal barrel flange (SA-350 LF2 Cl. 1) on the channel of an PWHT'ed exchanger that has a scar. The depth is about 1/8" and the raised face thickness is 1/4". I am wondering what the options are for repair, and what everyone things about the options i have listed below. Design pressure is 1970psi, temp is 300°F

1. weld metal build up then machine?
2. machine only, note that this will required at least 50% of the raised face to be removed.
3. ship off site to a local shop and have the nozzle replaced, and the channel re PWHT'ed....ouch!


I have concerns about using weld metal build up in high pressure service. Also, being that I could have ordered the flange in a flat face configuration, I feel that the raised face section can be machined because it is not needed for flange strength.

I have reviewed PCC-2 and it seems both one and two are acceptable.

 

[XL83NL]

Do you have a picture? Also, the fact you mention a 4" Cl 1500 barrel flange in combination with "being that I could have ordered the flange in a flat face configuration" is rather strange. I wouldnt suspect a flat face flange for such a high pressure application ...

 

[JG MechEng]

While it may be rather strange, it is an option and is also permitted to be ordered in that configuration per B16.5. It was just intended to point out that the raised face is not considered to contribute to the flange strength so it seems that the height of the raised face could be considered sacrificial. B16.5 says that the raised face section shall be 7mm unless otherwise ordered, so it seems to allow for less of a raised face section. Im not sure if I can apply this because it was not ordered this way, but was altered to have less of a raised face. Picture is in the link.

 

[racookpe1978]

Cheapest is to machine only the RF - but ONLY IF you can verify the depth of the scar is less than the RF height - Doesn't scale that way to my eye!

The RF is a critical part of the flange overall: It ensures of matching the gasket pressures and gasket fits to the flange and bolts. Yes, it could be machined off completely, but should not be. The machiing cost is NOT trivial.. (Using a Matabo grinder to hack it off is trivial cost, and a bad finish that will NEVER hold pressure properly.
Local weld build up and local "machining" is also likely to be done with a Matabo hand grinder and no preheat and no weld procedure. And most likely a final test leak as well.

You need to be able to find a field machining company that can mount a flange face machining tool on th flange, align it accurately, and then precisely cut off the height needed, leaving enough to maintain the gasket pressure. The group that scarred the face (company, fabricator, shipper, installer, whoever) needs to pay for that work repairing the scar.

 

[JG MechEng]

The scar is about 1/8" deep. Pcc-2 says I can leave 1/32" raised face and still claim it to be a raised face. We also have a contractor on site that has equipment to do this precision work in the field without weld metal build up. Thank you for the replies. I plan to have the raised face machined down to remove the scar, and the surface re finished. This should leave me with more than 1/16" of a raised face, enough to satisfy PCC-2.

 

[r6155]

Try with a mock-up, similar diameter but class 150..... and practice.
Make a similar scar on it.
Weld metal built-up and restore this little area by hand working (artistic).

Regards
r6155