Hello ,

As per ASME B31.3 ,LTCS material(A333 Gr.6) can be used at -104 Deg. C without impact testing requirements if the stress ratio (Sc) value is (~0.3) as per the graph in ASME B31.3.
My question is do we include the effects of temperature in to consideration while calculating the longitudinal stresses?How do I build the load cases to conform to the code requirements?

Thanks a lot in advance for your answers.
Rajan.

I'm interested in the answers to this as well.
We did something similar, and used cold
operating condition to determine local forces,
and from those manually figured out longitudinal
stresses (or more precisely, maximum longitudinal
stresses, as we did calcs in absolute). I think
we added pressure stresses as well.

-Shannon

I might get tripped up in a few details but to get longitudinal stress for this operating case, I would simly change the stress type from OPE to SUS.

Watch out for the SIF multiplier though. The implication (in Fig. 323.2.2B) is that no SIF be used so set your (Configuration Setup) "B31.3 Sustained SIF Multiplier" to 0.01 before error checking and running this analysis.

Raja,

This is very good topic. I have also had similar situation.

First, why do you check the stress ratio for this material ? Please understand A336 Gr.6 pipe material is for low temperature service but it is limited to -46 deg.C without impact test per B31.3(Table A-1 Note 6). However, this A336 Gr.6 pipe will be supplied with completion of impact test by mill as mandatory.
I am wondering if you are going to use A333 Gr.6 at –104 deg. C. Of course, you will not…because it is not a practical way. It will probably be type 316/316L austenitic stainless steel or other special alloys at this cryogenic service.

Second,
I assume your question is stress combination rather than material and you are going to use A106 Gr.B pipe at -40 ~ -20 deg.C. In this case, you need to check stress ratio if impact test is required with reviewing the minimum metal temperature-thickness combination.
As Dave mentioned, the SIF may not be required when making stress calculation. You can find a clue in the old edition of B31.3 para. 323.2.2.

B31.3,1999 edition stated;
“(3) Impact testing is not required if the design temperature is at or above –46 deg.C, and the maximum operating pressure of the manufactured components will no exceed 25% of the maximum allowable design pressure at ambient temperature, and the combined longitudinal stress due to pressure, dead weight, and displacement strain(see para.319.2.1) does not exceed 6 ksi. Use of stress intensification factors when making these calculation is not required”.

B31.3,2004 edition states;
“(3) Impact testing is not required if the design minimum temperature is below -29 deg.C but at or above –104 deg C and the Stress Ratio defined in Fig.323.2.2B does not exceed 0.3”.

I am wondering also….why there is so much different between 1999 and 2004 in same issue. The note (3) in Table 323.2.2, 2004 edition is very dubious to us.

Can anybody explain it clearly ????

The new figure 323.2.2A replaces the previosly used note 3. If the stress ratio is 0.3 or less (note 6 ksi is 0.3 times 20 ksi, a typical allowable stress for carbon steel), which is 0.1 or less times the tensile strength, there is not sufficient strain energy for crack propogation in a brittle fracture mode. Thus, you can use carbon steel down to -104C if the stress ratio is 0.3 or less.

The figure gives temperature adjustments between the 0.3 ratio and 1.0.

The stress ratio must include all stress, including stress due to thermal contraction. However, peak stresses need not be included, thus the note that SIFs do not need to be included.

The philosophy is the same as can be found in the ASME Boiler and Pressure Vessel Code, Section VIII, and the stress ratio chart is essentially the same as can be found in Section VIII, Div 2, which also has an allowable stress based in part on 1/3 ultimate tensile strength.