Nominal thickness off U-1A vs actual supplied material thickness

[NDTjoe]

Our NDT Technicians measured via UT the thickness of an in-service vessel shell wall to be around 0.350" thick.
The U-1A lists the Nominal Thickness as 0.250".
I calculated the min required wall thickness per ASME BPVC Section VIII para UG-27 to be 0.158". [ri=17.75", P=150 psi, S=20ksi (SA-516-70 @ 400F), E=0.85]
The corrosion allowance off the U-1A is 0.070".
0.158" + 0.070" = 0.228" ==> 0.250" plate nominal thickness. This makes sense.

My question is (assuming the UT readings are (close to) correct; I have no reason to doubt they are not):
Could it be the next size up (3/8") was used instead? (maybe supplier issues, already had 3/8" on hand, etc.)
And if another size material was used during construction (even if it exceeds the required thickness) should that be listed on the U-1A?
(it appears if not, the only way to know what the actual material thickness of a constructed vessel is to UT it once in-service)

Thank you,

Joe Jarvis
ASNT NDT Level III #211541

 

[david339933]

Possibly....but if 3/8" was used, it is required to be on the U-1A. U-1A requires nominal thickness of material used for the shell.

 

[NDTjoe]

Thanks David for the reply!

Ok good catch, the shell had a average measured thickness of 0.308" (ranged 0.283" - 0.312"), 5/16" is more likely.

Ok, am I reading you right, that the actual material nominal thickness used during construction should/must be listed on the U-1A?

If so the two conclusions (either/or fallacy, i know) are: the measurements were wrong, or they used something different than what was listed.

I should add, this is Deaerator Tank in Corrugator facility (make cardboard boxes), low low radar stuff, many have never been NDT inspected.
Its just another tank in the boiler room, quite neglected. The industry is just starting to take it seriously after some recent incidents, shenanigans I would not doubt happen and get through..

Thank you,

Joe Jarvis
ASNT NDT Level III #211541

 

[david339933]

Yes. Actual nom. thickness used for the shell must be listed.

 

[NDTjoe]

Ok thank you, the plot thickens, time for some phone calls...

 

[SnTMan]

NDTjoe, thickness tolerance per SA-20 for this thickness range (1/4" - 3/8") is max of +0.04" (over 120" wide), -0.01". So:

0.25 + 0.04 = 0.29, 0.25 - 0.01 = 0.24
0.3125 + 0.04 = 0.3525, 0.3125 - 0.01 = 0.3025
0.375 + 0.04 = 0.415, 0.375 - 0.01 = 0.365

Doesn't seem to jive especially well with the range of measurements, although 5/16" would make the most sense. Has any corrosion occured? Can you get MTR on the shell? Otherwise you may be stuck with guesswork...

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

Where are the drawings?

Regards

 

[NDTjoe]

SnTMan, sorry for the later reply (email had the alert email in junk folder).
Thanks for looking at the thickness range tolerances per SA-20.

Yes, some corrosion has certainly occurred, at least in pit areas. These vessels we inspect often have tons of dissolved oxygen and can be out-of-whack on their chemistry.
They are in Corrugating plants that makes boxes, and they tend to go down nearly every weekend, the transients hurt them. As far as any other reports, man, it is highly lacking,
many of these have never been inspected--ever. It is hard enough to get a U-1A in hand, let alone any history.

The discrepancy in thickness you mentioned could be due to the difference in the actual material velocity vs assumed.
There are often no areas of known thickness to calibrate to, so we will default to a somewhat conservative value of 0.2300 in/us, which is fairly close for the material, typically SA-516 Gr 60-70.

Regards,

Joe Jarvis
ASNT NDT Level III #211541

 

[r6155]

Pressure vessel without documents (drawings, nameplate, data report, etc.) it is scrap.

Regards

 

[r6155]

I worked in inspection company for several years. If I do not have the documents in my hands I do not inspect pressure vessels.
I am not complicit or irresponsible. I don't want to have problems with lawyers or judges. Pressure vessels are very serious things and responsible professionals are required to work in this specialty.

Regards

 

[oknow]

It is quite possible that the thickness recorded on the ASME MDR is incorrect, based on the UT thickness readings and that the shell is plate material.

I have reviewed many many MDR's that have errors in them.

If possible obtain the design documents to confirm.