Minimum wall thickness allowed as criteria for ultrasonic examination

[MechDesign105]

Hi yall!

I have been having quite a hard time with a question that seems so simple; what is the minimum wall thickness allowed when performing ultrasonic examination?

I thought that it would be the minimum wall thickness calculated as per the Code, however, I have found UG-16(c) and UG-79 that allow the final wall thickness to be under the calculated one.

How do I know then which is the minimum thickness allowed if it isn't the one calculated? Why is it not mentioned on the nameplate or on the drawings? Is this minimum allowable wall thickness supposed to be written in the Data Report?

Thank you!

 

[gr2vessels]

This is a good point to speculate on, but not much of the engineering. Perhaps a measuring caliper could have a tolerance larger than 0.01", so the calcs allows for this. Also, my copy of ASME VIII doesn't mention anything of this nature in UG-79, so no comment.
However, the old cook book is not perfect and the commitee is happily waiting for your proposal to improve it. I bet you'll find other contradictions too.
Cheers,
gr2vessels

 

[REGRUMBLE]

ASME Code basically leaves the min thickness up to the testing company. Most will tell you that anything less than 1/4" (which is the min by D1.1 or W59) is almost impossible but I have seen procedures tried on only 3/16" If the technician can prove they can find weld flaws in thin material welds the ASME code does not set limits.