API 579 ffs Fixing Negative RSFpit

[K_macisaac]

Hi there,

I'm completing a level two assessment for widespread pitting from section 6.4.3. I'm getting a negative RSFpit and for it to pass it needs to be a value greater than o.9. Combing through my calculations, I can see the negative comes from eq. 6.19, which I believe means the distance between pits is less than the diameter of the pits. Can I make these values zero? Does the vessel just now fail the assessment? Should I proceed to a level 3 assessment? I've attached an image of the pitting for reference.

Any guidance on this would be greatly appreciated.

 

[akpipelineengr]

I think that leads you to assume those pits are interacting and to assess them as a single pit or area of localized pitting (per part 5 and Figure 6.15).

Can you share some additional details about the vessel? Wall thickness, MAWP, pit depth, etc.?

 

[K_macisaac]

(if the excel attached) this is the analysis I did. If not attached, I inserted screen shots of the analysis. I have these negatives and I don't know how to proceed. They all originate because the pit widths are larger than P, the spaces between the pits.

 

[danb3]

Have you conducted a Level 1 assessment with the pitting charts? That methodology is more amenable to this kind of widespread and interacting pitting.

Looking at your data for the pit pairs, some of it doesn't really make sense though. For instance in pit pair 3, the larger pit is 3.7 inch in diameter, and is only 0.3937 inch away from the center of the smaller pit, which is 1.7 inch in diameter. This implies the second pit is contained entirely within the larger pit? Is there perhaps a unit error here?