API 653 interpretation

[AndresRP]

Hello, I have a question about the interpretation of paragraph 4.3.2.1 of API 653.
4.3.2.1 explains how to calculate the length L and how to find t1 and t2, but it does not explain what the distance between vertical lines is.
It also doesn't say anything about the distance between the 5 measurements vertically.

Can 4.3.2.1 be used to evaluate a band of corrosion around the perimeter of the bottom of the first ring that is caused by CUI?

What is your opinion?

Best regards

 

[IFRs]

4.3.2.1 c - "The authorized inspector shall visually or otherwise decide which vertical plane(s) in the area is likely to be the most affected by corrosion"

There is no specified number of vertical planes nor minimum or maximum spacing between planes. The inspector is authorized to choose the plane they think will be the worst case, sometimes that is not obvious so they try a few places.