Gents

Q) If corrosion allowance is entered in the Caesar input field, does Caesar take it into account for a B31.1 code stress compliance report?

Please could I be directed to a definitive forum reply on how B31.3 treats corrosion allowance and does Caesar incorporate corrosion allowance in the allowable stress calculations when working in accordance with B31.1. I am sure this topic has been well covered.

From the replies that Rich has answered, it appears that Zcorroded is indeed taken into account in the stress calcs.


I have also found this post from Rich Ay which is relevant:
The B31.1/B31.3 Codes state that corrosion is to be removed from the Section Modulus before making the stress calculation. Therefore corrosion has no effect on the system until the M/Z term is computed for the Code Stress.

My understanding of this is : removing corr. allow. maximizes the section modulus Z and minimizes the M/Z valueminimizes the stress

I have also found this:
Corrosion is considered in the minimum wall thickness calculation, and that is where the errosion and mill tolerance are also considered.

And this:
For the Codes that address corrosion, they state that "corrosion should be removed from the Section Modulus before making the stress calculation". So the full cross section is used in determining the stiffness matrix and in determining the load vector (system weight). It isn't until the stress is computed that "Zcorroded" is used instead of "Z".

B31.1 doesn't mention corrosion, so be default CAESAR II will not use the specified corrosion value. If you do want to force the use of corrosion, you have to alter the Configuration, and set the ALL_STRESS_CASES_CORRODED setting to "True". Once so set, corrosion will be deducted from the Section Modulus when making the stress calculations.

B31.3 on the other hand corrodes the Sustained and Occasional load cases, by deducting the corrosion allowance from the Section Modulus when making the stress calculations. If you want to corrode the Expansion load case, then you have to set the ALL_STRESS_CASES_CORRODED setting to "True".

Thank you for your valued reply Rich

When a client specifies a corrosion allowance and asks for a code compliance analysis to B31.1, I feel that good engineering practice should prevail and corrosion should be included by turning the ALL_STRESS_CASES_CORRODED setting to "True"

If the system is on the limit i.e. the pipe wall thickness is on the light side, the use of corrosion allowance will cause over stress.

I think good engineering practice excludes giving the client the option of including or excluding corrosion allowance based on the fact that B31.1 makes no mention of it - any comment on this?

Metals do corrode and good engineering practice must prevail and I feel corrosion allowance must be included. One wonders why the B31.1 committee in their wisdom excludes corrosion.

I will try get a B31.1 copy and investigate this issue further

Thank you once again for your input

Darril,
Have you found an answer to your question in B31.1? I've been looking through it and still couldn't find any corrosion allowance included in stress formulas. Flexibility analysis, ofcourse, is made using nomianal values.
And where does it state that corrosion allowance should be excluded from Z (section modulus) calculation?

B31.1 doesn't state that, B31.3 does though.