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Discrepancy Between U-1A and U-2A Forms

Discrepancy Between U-1A and U-2A Forms

Discrepancy Between U-1A and U-2A Forms

(OP)
We recently received a job for a Fitness for Service on a Vessel. I was going through the U-1A and U-2A forms and noticed that the minimum head thickness was different between the two forms. The minimum head thickness was lower on the U-1A form than the U-2A form. My original thought was to use the smaller of the two thicknesses since this would be more conservative. I've been searching through ASME Section VIII Division 1 code trying to find anything stating if I should use one or the other or what is acceptable, but I haven't been able to find anything. Has anyone else ran across this when doing a Fitness for Service?

RE: Discrepancy Between U-1A and U-2A Forms

First thought is that the thickness on the U1A should reflect the design thickness ( calcs) which would govern. The head having a thicker minimum is fine but it wouldn't fly the other way around. I would NOT recommend you increase it based on the info recorded on the U2A.

RE: Discrepancy Between U-1A and U-2A Forms

(OP)
That was my thoughts exactly. I just wasn't sure if there was a place in code that it talks about a situation such as this. Thank you for your comment.

RE: Discrepancy Between U-1A and U-2A Forms

Request for a copy of the design calculations and do your checks and balances.

I'd write the U-2A off to a typo or maybe missed the corrosion allowance, or who knows.

RE: Discrepancy Between U-1A and U-2A Forms

(OP)
Design calculations would be very helpful, but this vessel was designed and fabricated in 1993 and the design calculations cannot be procured at the moment. My assumption is that the U-1A was completed before the U-2A. It seems that the company associated with the U-1A assumes a 22% thinning for their shop and did there design calculations based of that. Where as the company that produced and actually fabricated the heads associate about a 5% thinning of their heads when fabricating. It's my understanding that the thickness given on the U-2A is the actually thickness of the heads as measured by the fabricator. The thickness of the heads given on the U-1A form is the thickness of the head that was assumed in the design calculations based on that shops 22% thinning allowance.

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