Fully Corroded for Pipeline Stress (ASM B31.4&B31.8)

Dear Richard,

I'm doing Stress Analysis for Pipeline with Code ASME B31.4 and ASME B31.8.

Would like to ask, What it means "Fully Corroded Condition" as "check" on configuration settings.

I've tried input as Thickness, Corrosion Allowance, and Fully Corroded (on configuration setting) as check.

Second input, I've put, actual WT minus CA itself, and put 0 mm on CA place, and left "Fully Corroded" as un-check.

I'm quite confused that result is different.

My intention is that,
to find out the stress result on all case (Sustained, Expansion, etc.) when Pipeline have already corroded, let's say after 20 years.

Would you please advice on this matter?

While I can't peek at CAESAR's code, I would suspect that when you input things correctly, it assumes a uniformly corroded pipe for purposes of strength, but a brand new pipe for purposes of weight calculation.

Thus, the second method (with the 0 CA) is "lighter" in the eyes of CAESAR, and therefore has several interactions. Support friction doesn't work as before exactly. Piping appears to be stronger.

But that would be my guess.

I haven't read B31.4, B31.8 so not sure they deduct corrosion allowance when they evaluate stresses.

When you set the 'All case corroded' option to be true, it will deduct thickness from an amount that you specified as corrosion allowance when you calculate the SUS, OCC and EXP stresses. When I had tested it for myself, stresses were greater(since section modulus reduced), but the weight wasn't changed.

In my opinion, IF you're piping line transfer corrosive fluid, then the option should be used. Otherwise, as long as code doesn't say to consider corrosion, then just don't use it.

Take a look at this old post about the matter,

http://65.57.255.42/ubbthreads/ubbthreads.php?ubb=showflat&Number=42550

CAESAR II takes a conservative approach on corrosion.
Corrosion will not be considered is setting pipe stiffness or pipe weight; that is, the F in F/A and M in M/Z will be based on full thickness.
When corrosion is applied in CAESAR II, the A in F/A and Z in M/Z will use the reduced wall.

Even fluids that aren't "corrosive" can remove wall material. Fluids with high velocities, rapid turns, containing solids, etc. can remove wall material. Likewise, all fluids remove wall material at some rate - given long enough service, any pipe will thin out.

It's up to the owner to define that. If it's up to you, then you should mention what you used, regardless of whether it's a good decision or a bad decision.

Reducing the wall thickness in the input (by subtracting the corrosion allowance) is very wrong. Firstly this reduces the weight of the system - which is incorrect. Secondly the thinner wall makes the system more flexible - which is non-conservative.

So manually reducing the wall thickness introduces two huge errors in the analysis of the system.

The "All_Cases_Corroded" option corrodes all load cases (by reducing A and Z as Dave discusses above).

Agree to Mr.Michael,

Even demi-water can remove the wall thickness due to unexpected internal fluid effect such as cavitation or else. Sometime it might be covered by margin between nominal thickness and minimum thickness, but often it doesn't.

Mr. Dave, what you mentioned above is that C2 deduct corrosion allowance even we set the basic code is ASME B31.1 not like the old post that I mentioned?

I assume you meant we turn on the 'all case corroded' option.

CAESARIII,

My response states how CAESAR II applies corrosion allowance in general. Specific piping code rules will supersede this statement.

Hi dave,

I understand that Caesar II doesn't consider the allowances for stress calculations for ASME B31.4; while "All cases corroed" is not be in "True".

So if I want to calculate the stress for the begin usefull life I have to select "false" for "all cases corroed", by other hand if I want to calculate at the end of the usefull life it must be in "true" (Im taking about B31.4)

Thanks