The re-pad needs to have a small hole drilled and tapped, say 1/8" npt, before the re-pad is attached to the branch connection. After the welds are completed, then low air pressure is applied thru the 1/8" npt. A soap solution applied on the welds shows very small leaks with bubbles. Larger diameter re-pads could be drilled and have small coupling ( 1/4 - 1/2") welded for connecting air pressure, as well as providing connection for 'tell tale' for optional in-service monitoring of possible leaks from corrosion perforation. If there are multiple sections of the re-pad separated by welds, then each section will need a test connection.
Some users specify plug to be installed after re-pad test.
Most re-pad test connections are left open with a covering of grease to seal out moisture. That way it can also show leaks in any following hydrotests.
Just one opinion to add,
Some client specifications ask yo provide one drilled hole (1/4" npt for example) for pads in nozzles through 12" and two drlled holes hor nozzles bigger that 12".
What pressure do you consider good fot the test?
Some clients specify 0.4 kg/cm2 (aprox 6 PSI).
The note about test pressure posted by nashof is a point well taken as I've seen s nasty accident when 120 lb shop air was applied to partially welded out repad.
We restrict repad pad testing to a max of 15 psig or pull a vacuum to get a differential of about 12 lbs. We mainly use the vacuum on SS vessels where we know there is a possibility of IGC in the nozzle to shell weld.
Yes, I have in my hand a copy of the API 650, ed. 2007. The Clause 7.3.4 reads:
"After fabrication is completed but before the tank is filled with test water, the reinforcing plates shall be tested by the Manufacturer by applying up to 100 kPa (15 lbf/in.2) gauge pneumatic pressure between the tank shell and the reinforcement plate on each opening using the telltale hole specified in 5.7.5.1. While each space is subjected to such pressure, a soap film, linseed oil, or
another material suitable for the detection of leaks shall be applied to all attachment welding around the reinforcement, both inside and outside the tank."
This is a standard procedure applied for pressure vessels ditto.
Cheers,
gr2vessels
