A333 Gr 6 Minimum Temperature

[FlashPurp]

Hello,

We are planning on using A333 Gr 6 piping in our design. The MDMT in B31.3 is -50 F and we have design conditions that may reach -55 F. I was told by by using the load case referenced
in B31.3 323.2.2 (a)(3) below and by reaching a stress ratio no greater the 0.95 that A333 Gr 6 material will be suitable to use at -55 F.

Referencing (23a) thru (23d) the equations given are only sustained loads. Do I only need to check the calculated sustained stress ratio to allowable stress but use 1 for the in-plane/out-plane moments? Would I use the allowable stress at MDMT? I am using Caesar II for stress calcs.



Thanks,

 

[georgeverghese]

Typically, this piping stress ratio route to allowing some exceedence on lower design temp is not used, since the actual stresses whilst in operation may well exceed what you compute in the design office. Since this is a marginal exceedence, see if the process engineer can calculate a higher resolution MDMT with some other simulation program.

 

[LittleInch]

I'm pretty sure you can A333 grd6 tested at lower temperatures down to about -60C which makes the problem go away. But is additional testing.

 

[goutam_freelance]

As per table 323.2.2A, up to a thickness of 12.7 mm -55 deg F minimum temperature can be used without impact testing.

For higher thicknesses, both table 323.2.2A and 323.2.2B can be used, in my opinion. The most restrictive minimum temperature should be used for obviating impact tests.

in B31.3 323.2.2 (a)(3) below

For combined stress, you need to consider all stresses, like pressure and dead loads, thermal and anchor displacement loads, torsional loads, etc.
Software like Caeser can calculate this stress at all points and find the maximum. The respective I factors should be input as 1.0 for this run.