Does CAESAR take out the mill tolerance while calculating Sustained section modulus and sustained stress using Equs. 23(a), 23(b) and 23(c) of ASME B31.3?

Thanks

MW

NO.
Mill Tolerance is used ONLY for Pressure Design purpose, e.g. Min. Required Wall Thickness assessment from Internal Pressure Load exclusively.
Read ASME B31.3 (or B31.1) Code.

Hi Doren,
Thanks for the reply.

The question is why it is not considered in sustained calculation? Para. 320.2 ASME B31.3 2014, Z is defined as "Sustained section modulus. Z in eqs. (23b) and (23c) is described in para. 319.4.4 but is computed in this paragraph using nominal pipe dimensions less allowances; see para 320.1."
In para 320.1 says "Section moduli used to compute stresses in this paragraph shall be based on nominal pipe dimension less allowances, i.e., the sum of mechanical (thread or groove depth), internal and external corrosion, and erosion allowances."

The question is why mill tolerance is not included in the term allowances?

There is a debate regarding the 12.5% mill tolerance; some say it is due to the misalignment of the mandrel during the pipe forming and if the thickness at one point of the section is less, it would be larger on the other point of the section and the modulus effectively remains the same. Other say mill tolerance allows the whole cross section of the pipe to be of 12.5% smaller thickness. In this case mill tolerance should be considered in the allowance to be taken out of the pipe dimensions for sustained stress calculations.

Just my thoughts

Regards

MW

As I see it - in B31.3 - mill tolerance is used only to confirm that the purchased wall thickness delivers sufficient wall to maintain the pressure boundary.

At this week's B31.3 meeting we reviewed a request for interpretation that mentions this (Item 17-3206):
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Q1: Does ASME B31.3-2016 include the mill tolerance on pipe wall thickness in the variable "c" in Eqn. (2)?
A1: No. For mill tolerance, see 304.1.1(a).

Q2: Does ASME B31.3-2016 require inclusion of the tolerance on diameter in the variables "d" and "D"?
A2: No.
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I guess you could say that B31.3 supports your "fatter on one side; thinner on the other side" scenario. Or, no matter what the tolerance, the pipe weighs the same.

It's relatively easy to monitor the mass of piping spools you output.

I'd hazard a guess that the location with most regular deviation from thickness would be for thick, rolled plate, which would be at the seam (thinner) and 180 degrees away (thicker).

Would subtracting 12.5% uniformly accurately describe the isotropic stiffness / stresses in such a scenario?

Could we accurately describe this setup without specifying seam direction?

Does isotropic stiffness even have a meaningful impact?

I suppose CAESAR 9000 could rotate every straight element in every direction in 0.01 degree increments until it arrived at a real worse case stress/strain scenario. It's only 36000 runs per element, to the power of the number of elements available...