NDTjoe
Industrial
- Jan 16, 2020
- 4
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
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