SA 36 for leg support on vessel in cold service

[sksmechanical]

Have a vessel that is in cold service. Using SA 333-6 for shell. Minimum design temp is -50F. Since legs aren't pressure containing wondering if SA-36 is still an option for leg material. Please advise.

 

[gr2vessels]

Yes, you can use it provided it comes with impact test certificate at -50F (I doubt that you'll get such certificate).
However, not entire leg will see the -50F, so you make the top attachment to shell of 333-6 and the bulk in 36.
Cheers.
gr2vessels

 

[vesselfab]

well since it's hard to flatten sa-336 pipe to flat to shape to an angle, i would just go ahead and use some sa-516-70 plate fabricated angles. check the thickness of the plate for minimum temperature. it's probably good for -50
at thin sections

 

[gr2vessels]

I fully agree, it's very hard to flatten the pipe and make an angle out of it;- then just use the pipe as is and make the legs out of pipe instead of angle. Is just as common as the angle.

 

[AK8824]

Support legs are not pressure containing parts. Hence they should be considered structural parts. A36 is used for technological structure. However, if one wants to apply the MDMT to the legas then using LTCS material would be appropriate. As such, A36 will not be certified for impact test at -50 F.

 

[sksmechanical]

I agree SA 36 is mainly for structural purposes as on the other CS vessels I have on my desk now I have used 36 for the legs but this is the first with a -50 MDMT. But would I still take into consideration that a worst case scenario that the vessel actually reaches that cold temperature shouldn't I specify probably 516-70 for the leg material? Are impact tests only legitimate for pressure containing materials?

 

[82253]

Couple options, depending on length of leg, vesselfab idea would work, if legs are long, extend broke plate legs to outside of insulation and weld A-36 angle to end. Other option would be use 304ss angle legs.

 

[sksmechanical]

Thanks for the information. I just specified 516-70N for the legs. Again thanks for the help everyone.