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

[atw257]

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?

 

[weldtek]

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.

 

[atw257]

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.

 

[bernoullies123]

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.

 

[atw257]

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.