Tapping via cold forming of a pressure vessel female threads

Question

Tapping via cold forming of a pressure vessel female threads

jennin77 (Mechanical)

(OP)

26 Sep 23 15:48

Hi all,

I have a supplier that would like to evaluate to product all the internal threads (integral flanged connections, threads UNC or 8-UN type machined directly on the vessel) with cold forming instead of machining.
Do you know if there is any guideline provided by the ASME for the type of manufacturing of female B1.1 or metric threads under pressure?
Not sure if there is any restriction for pressure containing threads.

Thanks a lot

david339933 (Industrial) · Answer 1 · 2023-09-26 16:55:28

RE: Tapping via cold forming of a pressure vessel female threads

david339933 (Industrial) 26 Sep 23 16:55

No, but you should see UG-43.

DKTim (Mechanical) · Answer 2 · 2023-10-22 16:14:10

To my knowledge the manufacturing method of threads is not addressed in ASME BPVC. The codebook uses the term "tapped" threads. When in reality we have many new technologies to manufacture threads:

Rigid tapping & thread cutting (material is removed/cut)
Thread milling (material is removed, but for blind threads the hole depth is nearly equal to thread depth)
Thread rolling (hot or cold, material is not removed)
Thread forming (typically used to refer to female threads, where the tap doesn't remove any material, it only forms the threads)

The use of the term "Tapped" has caused me grief each time we've switched AIs. Because we always thread-mill our studded flanges, and the code has specific requirement for hole depth in order to account for the extra depth of the hole vs the thread length.
But if you use a flat bottom drill and thread mill, the hole depth can be as little as 0.05" deeper than the thread depth.

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Tapping via cold forming of a pressure vessel female threads