A36/A992 Welded Pipe Support Attachments vs -20 deg F MDMT (not allowed per B31.3 with Imp Testing?)

[Vulture860]

With regards to welded piping attachments (structural shapes specifically, plate, etc), I have a project were MDMT = -20 deg F. Per my reading of B31.3, A36 and A992 materials Min Temp per Table A-1 puts you into Curve A of Fig. 323.2.2A and this states a design minimum temperature of ~+15 deg F for materials <= 0.394". According to this, impact testing would be required to use this material.

I believe this applies to welded pipe supports as well per Section 321.1.4 stating "Permanent supports and restraints shall be of material suitable for the service conditions"

Interestingly, our customer's own standards show A36 and A992 material for welded pipe support attachments and have no indication regarding additional impact testing.

Anyone here dealt with this before? Am I missing something here?

 

[ConstantEffort]

By the book, maybe impact testing would be required. In practice, many of my clients have not cared about structural attachments and the difference between +15F and -20F.

My clients declare an MDMT of -20F even in tropical areas just out of habit. They never require heat tracing because ambient never drops below +50F. They aren't worried about the pipes bursting and they certainly aren't worried about brittle failure of A36 at -20F. "Sound engineering judgment" allowed me to use A36.

Maybe you're in a similar situation?

 

[weldstan]

An MDMT of -20 is often cited in Engineering specifications even when operating conditions are not close to the MDMT. The actual operating (service) conditions will define compliance to 321.1.4. Isolated ambient temperatures down to -20 F does not define the compliance issue.

 

[GD2]

You guys are all correct. It's a very common practice to set the MDMT of -20F for standard steels in refinery and hydrocarbon process facility piping. No consideration is given to structural steel while writing the piping spec.
However, note that MDMT can be set higher than -20F for these steels depending on the fluid category.

Ganga D. Deka, P. Eng
Canada