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Cold bending T-91 Tube

Cold bending T-91 Tube

(OP)
ASME Sect 1 PG.20 gives specific direction for cold bending T-91 (bending below 1300f). The listed temperature ranges " post cold forming strain limits and heat treating requirements" detailing heat treatment/ begin at 1000f design temp ( the lower temp range).

What if the design temp is below 1000f? Do nothing?

RE: Cold bending T-91 Tube

You need to determine the strain from cold forming and use Table PG-20. If it is less than 5% you do nothing. If the strain is between 5 to 25% you perform a post bend heat treatment following Note 2 and if greater than 25% cold strain, you re-heat treat per Note 1.

RE: Cold bending T-91 Tube

(OP)
Thanks Met. I understand the calculation. Note the table starts at greater than 1000 degrees design temp. I find no mention of any requirement for what to do if the design temp is below 1000 degrees. I am inclined to believe nothing is required.

RE: Cold bending T-91 Tube

I would strongly suggest you perform a post bend thermal treatment at cold forming strains above 5% following note 1. Why? Because the creep rupture data I have reviewed shows a degraded creep rupture life having cold strains in CSEF steel. Granted below 1000 deg F, this is the sweet spot for this material, however, cold strain will impact long term creep rupture life.

RE: Cold bending T-91 Tube

(OP)
Understood and I certainly appreciate the advice regarding heat treatment.

Am I correct there are no specific heat treatment requirements for cold bending t-91 below 1000f design temp?

RE: Cold bending T-91 Tube

Yes, because of the low operating temperature.

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