calculate the thickness of gate valve for unlisted material based on ASME B31.3

[MoReSo]

Hello,

I need to calculate the thickness of gate valve for unlisted material based on ASME B31.3 - 304.1.
In this case as the valve is unlisted I don't have the related pressure to consider for the equation.

My question is that how can I calculate pressure for each temperature (100F, 200F,...)?
Is there any way to calculate pressure based on stress values for each temperature?

thank you,

Materials and Welding Eng.

 

[diferreira]

Why don´t you use B16.34 tables as a reference?

 

[MoReSo]

Because CD3MN IS NOT A LUSTED MATERIAL ( actually it's listed but under a wrong spec) and just B31,3 allows unlisted materials.

Materials and Welding Eng.

 

[racookpe1978]

So why can't use the calculation as a basis? I can use the seismic classifications for building being put up in a non-seismic area - I just have to recognize it might be a bit stronger than absolutely necessary. But then again, it might be cheaper to make it a bit stronger than the bare minimum allowed than to spend hundreds of hours trying to re-invent the pyramid.

 

[Danlap]

There are some approach for this:
1. Yes, in regards with "Table 1 Material Specification List: Applicable ASTM Specification" Material Group number 2.8. Your material supposedly equivalent with "Table 2-2.8 Ratings for Group 2.8 Materials" which written on the same book (ASME B16.34). Unless it is a very exotic material for special service, I seldom see technical specification (i.e. General Drawing) mention B31.3 as wall thickness calculation reference (it is either 16.5 or 16.10).
I believe it would not deviate a lot from this table. If yes, anyhow your final product valve still have to undergo 1.1x and or 1.5x Full DP test, which for sure covered yours and your client doubt.

2. The hard way, revert back to your casting vendor and ask for P/T rating. If still not sure, make a valve prototype out of this and test the valve at approximately full DP (in regards with ASME 16.34) and test it at minimum design temperature, ambient and then maximum design temperature. Take the prototype after each test and look under microscope for the micro structure analysis (deviation). This should be done in a lab and witness by ASME representatives.

It is good to hear that you undergo the calculation. If you find considerable deviation it would be very interesting. However kindly note that this will be installed in an ASME standard pipeline; almost no manufacturer would re-fabricate casting mold (in regards with wall thickness) just in order to conform your material (unless you order more than 1000 valve or pay a lot for it). The corrosion allowance of the valve naturally will be bigger than the pipeline itself.
The composition is always the same 22Cr–5Ni–3Mo–N either for Forging / Bar A182 F51 and casting A351 CD3MN.