ASME B31.3 Mill Tolerance
ASME B31.3 Mill Tolerance
(OP)
Is there any way to avoid using the full 12.5% mill tolerance in pipe wall thickness calculations and still be ASME B31.3 code compliant?
Can the wall thickness be measured and applied in the calculations without the mill tolerance? Or with a reduced mill tolerance?
I have an existing pipe spool in which the 12.5% mill tolerance is just causing my wall thickness to be inadequate. Reducing down to 8% mill tolerance would allow my wall thickness to pass.
Is there any case where you can reduce the mill tolerance if the exact wall thickness is known / verified?
Thank you in advance.
Can the wall thickness be measured and applied in the calculations without the mill tolerance? Or with a reduced mill tolerance?
I have an existing pipe spool in which the 12.5% mill tolerance is just causing my wall thickness to be inadequate. Reducing down to 8% mill tolerance would allow my wall thickness to pass.
Is there any case where you can reduce the mill tolerance if the exact wall thickness is known / verified?
Thank you in advance.





RE: ASME B31.3 Mill Tolerance
I don't understand that part. What do you mean by reducing down to 8%?
RE: ASME B31.3 Mill Tolerance
RE: ASME B31.3 Mill Tolerance
6" STD Pipe
= 0.280" wall * 12.5% = 0.245" minimum wall thickness required.
= 0.280" wall * 8% = 0.257" minimum wall thickness required.
RE: ASME B31.3 Mill Tolerance
Then you would need to order material that meets that, can you do it?
There are some sources of min wall pipe, that would be 0.280" min wall.
Most pipe specs let you invoke that option, though finding such material may be very difficult.
You may just want to go to sch80.
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P.E. Metallurgy, Plymouth Tube
RE: ASME B31.3 Mill Tolerance
Long story short, my pipe thickness is not enough after subtracting the 12.5% mill tolerance. If I only subtract 8%, my pipe wall is adequate.
Does ASME B31.3 allow for any mill tolerances other than 12.5%?
RE: ASME B31.3 Mill Tolerance
Is there anyway to verify the pipe wall with UT thickness gauge and apply these thicknesses while still being code compliant?
RE: ASME B31.3 Mill Tolerance
The only option you have is what EdS mentioned. DVWE's reply is incorrect, thinking the wrong way around.
RE: ASME B31.3 Mill Tolerance
Then yes, you can verify the actual wall thickness of the spool(s) with UTT and as long as they are not less than the minimum required wall thickness (after subtracting 12.5%) they are fine.
RE: ASME B31.3 Mill Tolerance
RE: ASME B31.3 Mill Tolerance
If we subtract the 12.5%, we do not meet the thickness requirements in B31.3 equation 304.1.2.
RE: ASME B31.3 Mill Tolerance
I am not sure that you can get away with saying "we bought X, and it came in above the minimum so it works", that is just luck.
You would have to make sure that all of the drawings for the unit make clear that these are not regular sch40 pipe and cannot be replaced with sch40 pipe.
I think that you need to show that you bought material that meets the requirements, and you clearly did not.
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P.E. Metallurgy, Plymouth Tube
RE: ASME B31.3 Mill Tolerance
If they are not, then I agree with Ed.
RE: ASME B31.3 Mill Tolerance
It only works for that pipe or set of pipes.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: ASME B31.3 Mill Tolerance
Regards,
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: ASME B31.3 Mill Tolerance
But your drawings will have to be updated so when the spools are replaced in the future the pipe used has the same checks.
The 12% is there to allow for seamless pipe to have the bore/hole off centre. If was 12.% under everywhere it would not meet weight/length tolerance.
We have for projects specified pipe with 5% tolerance, which is easy for pipe made from plate.
RE: ASME B31.3 Mill Tolerance
Regards
r6155
RE: ASME B31.3 Mill Tolerance
RE: ASME B31.3 Mill Tolerance