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Need to drill a hole in blind flange to weld pipe

Need to drill a hole in blind flange to weld pipe

Need to drill a hole in blind flange to weld pipe

(OP)
Need to weld 2" SCH 80 A106-GrB pipe by drilling a hole on 3"x150# A105N blind flange. Per B16.5, table 6; allowable smallest size of hole for 3" blind flange is 1 1/4". Is there any way (in B31.3 or ASME VIII) than can support this modification ? Operating pressure/temp is 5 bar and 130 Deg C, design pressure/temp is 15 bar and 170 Deg C.

RE: Need to drill a hole in blind flange to weld pipe

Through VIII-1, U-2(g).

RE: Need to drill a hole in blind flange to weld pipe

Use a hubbed blind or a reducing flange.

RE: Need to drill a hole in blind flange to weld pipe

Moltenmetal's suggestion is the better one if that is a viable option.

RE: Need to drill a hole in blind flange to weld pipe

(OP)
Thank TGS4 and Moltenmetal for your suggestion. Unfortunately, reducing flange or hubbed flange is not an option.

So, for solution per option through Section VIII, div 1; does it require a typical flange design to meet this specific custom requirement ? Any more details, clause, equation from VIII, div 1; is appreciated. Thanks,

 

RE: Need to drill a hole in blind flange to weld pipe

Hi David19,
Turn the table around and instead of welding a pipe in the blank flange opening, weld a slip-on flange machined from a blind flange to the end of a 2" pipe. That is an ASME VIII design.
Cheers,
gr2vessels

RE: Need to drill a hole in blind flange to weld pipe

gr2vessels,

Normally, I would agree with you, and I have done that many times.  However, care must be taken since a drilled blind does not have the same thickness (at the hub) as a slip-on flange.  I would agree with the procedure if the necessary Appendix 2 calculations are performed on the flange.

RE: Need to drill a hole in blind flange to weld pipe

The flange is likely to fail the Appendix 2 calc.  ASME B16.5 flanges are frequently over-bolted and fail on bolting stress.

You need a hubbed blind or reducing flange, or you're going to have to de-rate the assembly to less than the full flange class.

RE: Need to drill a hole in blind flange to weld pipe

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