Repads for Pressure vessel
Repads for Pressure vessel
(OP)
We are fabricating a Pressure which had repads for nozzles and manways. These repads are cut in two pieces and fitted on the nozzles after the full penetration category "D" joint is welded and PT tested. two tell tale holes are also drilled.
After welding the repads, we carry out a 15 Psi Pneumatic test on the pad. It was observed during one of our test that while applying pressure to check one side of the repad, air was coming out from the other tell tale hole. There were no leakages in the weld fom inside and outside.
My question is what is the reason of the air coming out from the tell tale hole when the two halves of the pads are welded
After welding the repads, we carry out a 15 Psi Pneumatic test on the pad. It was observed during one of our test that while applying pressure to check one side of the repad, air was coming out from the other tell tale hole. There were no leakages in the weld fom inside and outside.
My question is what is the reason of the air coming out from the tell tale hole when the two halves of the pads are welded





RE: Repads for Pressure vessel
However, you did not explain or mention how you joined the two repad halves along the split line. My guess is this is not a full penetration weld and this is where the air is going between the two repad halves when you pressure test.
RE: Repads for Pressure vessel
RE: Repads for Pressure vessel
Sounds like you think that the weld defect is acceptable that allows leakage to the other side of the repad. I'd be concerned that the lack of penetration of the repad butt weld into the vessel shell could be a crack-like defect. I suggest that it be investigated as to nature and extent.
Steve Braune
Tank Industry Consultants
www.tankindustry.com
RE: Repads for Pressure vessel
I'm no more concerned than if this were a single plate with the void all round. Probably do more damage removing the weld(s).
RE: Repads for Pressure vessel
Nor would I if that were true. The leak is a sign of a weld defect of which its character can not be known. Since many weld defects end up crack-like in nature, the leak should not be accepted without further verification.
Steve Braune
Tank Industry Consultants
www.tankindustry.com
RE: Repads for Pressure vessel
RE: Repads for Pressure vessel
Could it be a material defect/lamination? Maybe it is just a weld defect,but if this was designed as a full pen weld this is not acceptable.
To me it is a different matter about acceptable levels of inspection. In my book this would require a nonconformance and a evaluation.
RE: Repads for Pressure vessel
RE: Repads for Pressure vessel
If it was possible to avoid that this weld fuses also part of vessel wall, I think this would desirable, to avoid possible damage to the main wall. A copper backing strip is an example, though this would create a highly undesirable space between the repad and the wall: however it is clear that in such case air would freely traverse from one hole to the other without any concern.
There are so many problems in building a good vessel: no need to create new ones.
prex
http://www.xcalcs.com
Online tools for structural design
RE: Repads for Pressure vessel
From the first post it appeared as they did not expect a leak. So...I ask. Did the design call for the repad joining weld to be attached to the shell? If so then there may be another defect. The repad may be fine by itself as you suggest. I see another issue.
If I had to make a call on this I would return to the weld joint design for what was specified. If it called for,say a V grove with a 1/4" open root. I would call the leak a problem.
RE: Repads for Pressure vessel
Steve Braune
Tank Industry Consultants
www.tankindustry.com