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Can anybody please guide me how to design miters?

Here is a file attached on Miter design, Hopefully it may Answer your basic need.

Can you please explain a bit about 'A' and the way to calculate 'T' (thickness of miter).
It would be nice if you please share a sample calculation of a miter.

What is your design code for piping?

We have to design a miter for a 42"NPS piping standard schedule against B31.3
The design pressure is 100 psi and design temperature is 200 deg F. It's carbon steel material piping conforming to A106 gr. B

You just refer to the document attached by Usman and I will take you through.

1. Miters can be designed as a single piece or as multiple. The difference is the pipe pieces (two or more than two) for multiple miters and the angle 'theta' restricted to maximum 22.5 deg whereas in a single miter the angle can be above 22.5 deg but less than 90 deg.

2. The calculations as per ASME B31.3 are the maximum allowable pressure values which you have to check by iteration (changing the values of 'theta' and thickness 'T').

3. Start with selecting multiple miter case with 'theta' at 22.5 deg. For the first iteration, assume a thickness for miter 'T' as straight pipe thickness.

4. From geometrical drawing layout, see the value of R1 which should be greater than the value mentioned in the file attached by Usman or eq. 5 of 304.2.3 in ASME B31.3

5. Now use the formula 4(a) of 304.2.3 to see what's the allowable pressure comes out to be.

6. Then use the formula 4(b).

7. The pressure lesser of the two evaluated from equations 4(a) and 4(b) of 304.2.3 would be the allowable pressure.

I hope I haven't missed out anything and it would guide you in designing the miter for your case.

Feel free to seek any help.

Yup tahnks ben for the elaboration. Here is attached more detailed form of the above doc extracted from B31.3. Interesting discussion hopefully shall conclude some valuable outcome.

Thank you all for the help.
I will make the calculations and seek advise if required.