thickness loss evaluation- ASME VIII Div 1 vessel with 0 design corrosion allowance 1

[Muhaka22]

An ASME VIII Div 1 vessel with 0 design corrosion allowance has thickness loss on the shell and nozzles.
>Can I calculate the minimum design thicknesses of these components using the original year 1995 design code and then use these as an additional margin compared to the actual vessel thicknesses? The actual/measured thicknesses are 20-30% greater than the calculated values, which is apparently an extra design margin/FOS that has potential to be used.
>Or should I conduct an API 579 analysis directly?

Best regards

 

[r6155]

If actual thickness is 20-30% greater than calculated values, what are you looking for?.

Regards

 

[Muhaka22]

I just want to confirm if this approach is correct. Can the original code be used this way , or is an API 579 FFS assessment necessary once the corrosion allowance (if any) of a vessel is exceeded?

 

[JStephen]

ASME VIII Div 1 is a construction code, not a maintenance or evaluation code. See the national board code, etc. for those purposes.

https://www.nationalboard.org/Index.aspx?pageID=4

 

[FacEngrPE]

Depending on where you are the Authorized Inspector (may be jurisdictional or working for your underwriter) can be consulted regarding the local requirements. Most often they repeat the National Board inspection Code (see previous post).
The reports I have seen use actual thickness for the calculations, per the jurisdictional requirements. If corrosion is not uniform, the thinnest location is used as the thickness.

Regarding API 579, it can be used with the National Board Inspection Code, it does not suppliant it.

https://www.odonnellconsulting.com/resources/introduction-to-api579/[/URL]]API 579 / ASME FFS-1 Fitness-For-Service
Fitness-for-service evaluations performed in accordance with this Standard are recognized and referenced by API 510 (Pressure Vessel Inspection Code), API 570 (Piping Inspection Code), API 653 (Tank Inspection, Repair, Alteration, and Reconstruction), and by NB-23 (National Board Inspection Code) as suitable for evaluating the structural integrity of pressure vessels and related equipment.

 

[Muhaka22]

Thank you for your responses, @FacEngrPE and @JStephen . Can you please guide on the relevant section of the code dealing with such issues? I am not from the US, and haven't used the code before.