drill and tap hole

[mowlin]

Can anyone tell me if when a hole (1/2" npt) is drilled and tapped in a blind flange for hydro testing purposes if the flange is derated and to what rating? 36" 3003 BF; any info please

 

[rustbuster]

Yes it is de-rated. Typically flanges are drilled and a welded coupling is added as the threaded connection.

 

[Cockroach]

The code specifically forbids the removal of metal from any ANSI rated flange. Drill and tap of a 1/2 FNPT hole definitely removes material, therefore under the strictest sense of the code, it is derated.

I've practiced seasoned judgement on these ones, 36 inch blind flange with a minimum of volume removed, doesn't make much sense. As long as the intended use of the blind flange is not operationally compromised, then you can use it although the ANSI rating would need to be removed. You would probably be more than safe using it in your bastardized condition.

Grind the numbers and be sure, have a PEng sign off on it and stamp it certified for use. (In Canada only)

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada