How to calculate Thermal strength on ASTM A995 J93404 1

[asbjornr]

Hi,
I am currently calculating the shell test pressure for valve bodies in various materials and temperatures.
This is done in order to find the weakest state of the valve body, and from that state determine ambient test pressure.
This is no problem as long as I can find Temperature/pressure ratings in ASME II-D. However, the newest materials are not listed there, and with a new edition every third year it can be a long time waiting. Can someone help out with further information?

I have the ASTM A995 standard and ASME II-D 2007.
I have been informed that ASTM A995 will not be implemented in the ASME II-D 2010 edition.

Many thanks,
AsbjornR

 

[metengr]

asbjornr;

I am currently calculating the shell test pressure for valve bodies in various materials and temperatures.

What?

This is done in order to find the weakest state of the valve body, and from that state determine ambient test pressure.

What?


If the valve bodies are manufactured to ASME B16.34, you have a listing of qualified materials along with working pressures of the valve body as a function of service temperature.

What are you trying to do with the above? I am at a loss.

 

[asbjornr]

Hello metengr,
Sorry, I didn't explain the problem well enough.
The problem occurs when the temperature is outside of ASME B16.34; which lowest temerature is -29C.
I work with valves for LNG, LEG and LPG which have temperatures -163C, -101C and -46C, thus I need working pressure according to class, or Yield strength and Tensile strength values for that temperature range. Any help in this issue would be highly appreciated.

AsbjornR

 

[metengr]

asbjornr;
Thanks for the clarification. Here is an excerpt from ASME B16.34

2.3.2 Low Temperature. The pressure rating for service
at any temperature below ?29°C (?20°F) shall be
no greater than the rating shown in Table 2 for ?29°C
(?20°F).

It would appear that for valve materials suitable for lower temperature service, Group 2 and Group 3 (like the cast austenitic or Ni-base metals), below -29 deg C, you must use the working pressure rating for -29 deg C for lower temperature service. It does not prohibit the appropriate materials for lower temperature service.

 

[asbjornr]

Thanks metengr,

then it should be ok using ambient working pressure even at low temperatures as long as it's a group 2 or 3 material without further calculations.
I assume that the fact that some of these materials in group 2 or 3 are becoming weaker in a cold state, still allows ambient working pressure because it is covered by the minimum wall thickness tables. Am I thinking right?

AsbjornR

 

[metengr]

asbjornr;

I assume that the fact that some of these materials in group 2 or 3 are becoming weaker in a cold state,..

No, they are not weaker in strength becausae of lower service temperature. The Group 2 and 3 materials are considered austenitic materials and do not exhibit the charactersitic ductile-to-brittle transition temperature behavior. The austenitic stainless steels in Group 2 could contain some level of ferrite by design, but this would only effect notch impact behavior at service temperatures well below what you have stated.

Bottom line is that the Group 2 or 3 valve materials will maintain the same pressure rating used at -29 deg C for lower temperature service.

 

[asbjornr]

Hi metengr,
Yes of course, now I understand.
Many thanks for sharing your knowledge.

AsbjornR