Weld Efficiency for VIII-1 Vessels – Section UW-11(a)(5)(b)

Comment: Only ASME can make interpretations on the ASME VIII-1 Code


Illustration for Weld Efficiencies

The vessel from the weld efficiency notes – hemi left head, straight shell and SE or F&D right head

I have long struggled with the weld efficiencies presented in section UW of the ASME VIII-1 code. I have had more trouble with it than many other sections of the book combined. The ideas in this section are simple, but the ASME code written around it is anything but. Where ASME has not made the code readable, we must live with confused and diverging interpretations.

The problem area is sections UW-11 and UW-12 and any section of the code that references UW-11(a)(5)(b) – and there are many. What weld efficiencies to use when seams with different efficiencies intersect? I do not believe that circ weld efficiencies can affect longitudinal efficiencies however; these rules as presented in UW-12 and UW-11(a)(5)(b) exist and must be dealt with. I do believe that I will have to read the infinitely confusing sentence UW-11(a)(5)(b) many more times in my career.

Only ASME can provide interpretations as to what this code means, and someone can ask them, but – how about doing something simple instead? Samples of what the code committee wants can be found in appendix L. In specific samples L-1.5.1 through L-1.6.3 show the correct weld efficiency to use with differing radiography, and they also show the effect of circ efficiency on long seams. The meaning of UW-11(a)(5)(b) can be inferred.

This article comments on the 6 sample vessels found in Appendix L. A simple spreadsheet is introduced that calculates the same weld efficiencies (see below). The spreadsheet can be downloaded below. Each Appendix L sample is calculated at the end of this article.

Pressure Vessel Engineering Ltd. assumes no responsibility for this sheets use, and reminds you that only ASME can provide code interpretations. We would however be very happy if everyone could use the same interpretation to this difficult code section.

Update: Oct 2014

ASME has withdrawn the sample calculation Appendix L from ASME VIII-1 and released PTB-4-2013 ASME Section VIII – Division 1 Example Problem Manual as a replacement. The old Appendix L and the new PTB-4 disagree on when UW-11(a)(5)(b) has been met and the resulting weld efficiency. We are leaving the Weld Efficiency Notes posted as we and others have used the logic to design many vessels, but we are not longer using it going forward. The appropriate comments have been added to the document indicating what has changed. The weld efficiency calculator has been removed from this site.

We are preparing a request for interpretation for ASME to further clarify how to use UW-11(a)(5)(b) rules.