Internal / External Corrosion Allowance

Hi,

Please could someone help answer the following CAESAR II related question?

I have a requirement to model a riser (to DNV code) using CAESAR II and have to account for an internal corrosion allowance of 1mm but also 6mm external allowance. Looking at the way CAESAR II is set up, there is only one input box for corrosion which I assume is only for internal. If this is the case, can someone explain how I should account for the 6mm external corrosion allowance?

My thoughts were to do one of the following:-

1. Add 6mm to the input corrosion box making the corrosion 7mm in total (not sure if this is technically correct)

2. Reduce the pipe OD by 6mm and keep the corrosion input box as 1mm for internal.

Any thoughts / advise would be much appreciated.

It's more effort, but here's what you might do:
OD = new OD
OD* = OD as input into CAESAR
WT = new WT
WT* = WT as input into CAESAR
ICA = internal CA
ECA = external CA
INS = Insulation thickness

CA = ICA
OD* = OD* - ECA
WT* = WT* - ECA
INS = ECA

Insulation density = metal density.

Note: You will want to model bends and tees the "normal" way and this way and compare calculated stiffnesses and SIFs, to ensure this approach makes sense.