SIF an Corrosion Allowance

[saplanti]

Greetings,

I have not thought about it before, but one of my fellow engineers asked me after I handed in my spreadsheet for SIF calculation, and my calculation spreadsheet did not include the corrosion allowance either.

I have checked ASME B31.3 Table D300 for Flexibility factor and SIF, and could not find the answer I was looking for. The table Notes (4) is defines:

Tbar = for elbows and miter bends, the nominal wall thickness of the fitting,
Tbar = for Tees, the nominal wall thickness of the matching pipe.

I have thought that the code calculations are based on the corroded wall thicknesses, and the code does not support it in any way as far as I checked.

In case there is a small corrosion allowance available the value does not change much. But if the corrosion allowance is 3 mm and greater the changes become very large with small diameter pipe sizes.

At the moment I do not have Caesar II software to check to see what Caesar II considers for the SIF calculation.

Therefore, I would like to get your valuable opinion on the issue.


Thanks in advance and kind regards,

Ibrahim Demir

 

[saplanti]

Greetings again,

It is interesting that the only code CODETI C3.2.6.3 Notation for "ef" gives the following explanation for the thickness in SIF applications:

"ef = Thickness of reference used to calculate the constraints: the half-thickness a range of tolerances and c1- c1+ less corrosion allowance or possible erosion (see Note 1 and 2).

Note1. The determination of the stress from a well defined thickness can be very conservative in so far as the corrosion or erosion leading to sub-thickness are in the vast majority of localized cases.
In agreement with the Principal validation behavior for the network can be based on a verification of the constraints taken into account these phenomena only for areas potentially affected."

The translation into English may not be 100% correct but the concept is more or less defined.

I guess this is valid for all the standards; however I still can not get this validated by ASME B31.3.

Regards,

Ibrahim Demir