Take a look at the requirements of the height of raised face as per ASME B16.5:
ASME B16.5 Flange – Regular Raised Face Height
Typically, the height of Raised Face of ASME B16.5 Flange is divided by Flange Class by:
1- Flange Class 150 and 300 which have the Raised Face Height around 2mm.
2- Flange Class 400 and above have Raised Face Height around 7mm.
When damage occurs on Flange’s Raised Face, the method to repair without welding works as per ASME PCC-2 can be done by machine, removing the damaged parts and refinishing the Raised Face again. Then do MT or PT to ensure that the Raised Face has no more defects.
In order to re-machine the Raised Face, the height of the Raised Face will be lower than the original. ASME PCC-2 requires that the remaining Raised Face height must not be less than 0.8 mm of the minimum required height. So it’ll be able to bring Flange back to use by machining without welding works.
AMARINE 
Hello, I am a bit confused with the statement “must not be less than 0.8 mm of the minimum required height”.
For 600# flange, raised face is 7mm, I can machine it up until 6.2 (0.8mm) or until 0.8mm?
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Hello, I am a bit confused with the statement “must not be less than 0.8 mm of the minimum required height”.
For 600# flange, raised face is 7mm, I can machine it up until 6.2 (0.8mm) or until 0.8mm?
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