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ASME 16.5 Standard Flange Thickness

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Mr. P

Mechanical
Oct 26, 2020
5
Dear Experts,

I would like to obtain the minimum thickness of the standard flange for in-service equipment or piping where undergone crevice corrosion resulting in wall loss on the flange thickness.

With regards to the minimum thickness of the standard flange in accordance with ASME 16.5, clause 7.4 Flange Thickness mentioned:

Required tolerances for flange thickness are as follows.
NPS ≤ 18, +3.0, −0.0 mm (+0.12, −0.0 in.)
NPS ≥ 20, +5.0, −0.0 mm (+0.19, −0.0 in.)
The plus tolerance is applicable to bolting bearing surfaces whether as-forged, as-cast, spot-faced or backfaced.

Could you please advise how to derive the minimum thickness with includes the bolting stress or bearing? Is there mentioned anywhere in the codes or calculation methods?

 
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There are no under tolerances allowed if you want the flange to remain as a B16.5 flange.

Your only option is to calculate according to ASME VIII app 2 and accept a lower design pressure than whatever the flange currently is rated at which will impact your entire system or cut out and replace the flange.

Some numbers might help here.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
 
If you are talking the actual flange thickness like you mentioned in clause 7.4, then LittleInch is correct. However, because that surface isn't in contact with the process it's not likely to corrode due to internal factors, only external. If you are talking about internal pipe corrosion then you just need to do a pipe calculation (based on the thinnest part of the hub) to ensure the corroded state is still thick enough per code.
 
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