SS 321H- minimum heat treatment temp 1095 deg C.

[insider79]

Hello members,

1. I'm calculating WT to purchase A312-TP321H seamless pipes for design conditions 800°C at 3.5kg/cm2. For thk >3/8", ASME B31.3 mentions note 30 against it in Table A-1 which states "For temperatures above 538°C (1,000°F), these stress values
may be used only if the material has been heat treated at a temperature of 1 093°C (2,000°F) minimum".
However I do not find this note for thk <3/8". The WT that I've calculated are lower than 3/8". So, should I apply note 30 to WT<3/8" too as precautionary measure? Please advise.
One of the reason I think note 30 is not mentioned for <3/8" thk could be that if pipes are cold worked then such high temperature treatment could reverse the benefits of cold working. I'm guessing though, not sure.

Thanks
Regards

 

[weldstan]

If the operting conditions are near design or above 1000F, why do you think any cold work strength efect will remain for any real length of time?

 

[insider79]

@weldstan. Thanks for your reply. I am wondering why ASME B31.3 does not apply “For temperatures above 538°C (1,000°F), these stress values may be used only if the material has been heat treated at a temperature of 1 093°C (2,000°F) minimum" for <3/8”? Should I consider this requirement for WT <3/8”?

 

[weldstan]

I believe you should. Way back, over 45 years ago, we saw pemmature failures in 321H operating above 1000F where the heat treatment was closer to 1850F - 1900F. We were informed by a number of manufacturers and researches that the heat treatment should be higher, 2000 - 2100 F as I recall.