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# Terms in API 650 5.10.5.2

## Terms in API 650 5.10.5.2

(OP)
In API 650 section 5.10.5.2 stated "The participating area at the roof-to-shell joint shall be determined using Figure F.2 and the nominal material thickness less any corrosion allowance shall equal or exceed the following:"

The sentence nominal material thickness less any corrosion allowance here does it refers to corroded thickness?

### RE: Terms in API 650 5.10.5.2

The nominal material thickness is the calculated or minimum design thickness of the standard calculated in Section 3.6 Shell Design. You are not adding any additional thickness for corrosion. Therefore, if the nominal minimum thickness is 0.25", but you constructed it at 0.30, you'd have 0.05 corrosion allowance.

### RE: Terms in API 650 5.10.5.2

(OP)
I understand regarding the nominal thickness. However in this sentence the word "less any corrosion allowance", so does this refers to the corroded condition of nominal thickness minus the corrosion allowance?

### RE: Terms in API 650 5.10.5.2

takiyasamsama -

To the question in you your second post: This section requires you to use the corroded thickness in your calculations.

Let's clear up what "nominal thickness" means in this standard:

API 650 12th edition Addendum 2 Errata 2:

3.22
nominal thickness
The ordered thickness of the material. This thickness includes any corrosion allowance and is used for determination of PWHT requirements, weld spacing, minimum and maximum thickness limitations, etc.

3.4
corroded thickness
A design condition equal to the nominal thickness less any specified corrosion allowance.

### RE: Terms in API 650 5.10.5.2

(OP)
Thanks IFRs for clearing that up. I forgot that this is mentioned in Section 3.

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