American Welding Society Forum
I am working on a procedure for the testing of the seal welds on the duct work of a SCR. I can do either Diesel or a vac box test.
I remember back in the day when I used to work at a ship yard and we test the watertight bulks heads, we would air test them.
The procedure entailed spraying a water/soap solution on one side of the seal weld and run an air lance of sorts along the opposite side of the weld. Any path through the weld or welds would immediately show up in the form of bubbles.
My question is has anyone tried to do this on seal welds in a duct work application? I have approached my counterpart client side and if I can prove the concept and demonstrate it. They may buy into it.
Any thoughts or suggestions?
Diesel is thinner than water, so will show evidence of a leak that is too small for water to pass through.
Air is thinner than diesel, so will show evidence of a leak that is too small for diesel to pass through.
Vacuum box testing of segmented areas is an option, but is highly susceptible to operator error and is very labor intensive.
Leak testing of large areas with air is far cheaper than with diesel.
When leak testing with air, you must be careful to avoid over pressurization, which will damage the structure and/or cause a violent explosion. All you need is about 2 psi.
A simple yet very safe air testing inlet and safety pressure relief mechanism is to attach a length of 2" pipe to the duct to be tested that is a foot or two long. The pipe will have a compressed air inlet connected to the side with a ball valve that acts as a simple pressure regulator,meant to throttle the release of the compressed air into the duct.
The end of the pipe will have a loose fitting slip fit plug that weighs about 2 pounds. When the pipe is installed in the vertical position, gravity keeps the 2 pound loose slip fitplug in place to seal the end of the pipe, until the internal pressure reaches about 2 psi. Then the loose slip fit plug will float in place when the internal pressure reaches about 2 psi. If too much air pressure is introduced, you'll blow the plug out and risk damaging, but not exploding, the duct. Regulate the incoming air flow until the plug floats just a bit from the end of the pipe.
This process does not provide and exact or chartable pressure, but simply and cheaply allows soap bubble testing of the duct or compartment exterior.
Unlike with diesel, this test method allows immediate, efficient weld repair of any found leaks. Simply shut off the air while the repair is being made, then restart the flow immediately after.
Also, this test needs to be completed prior to any coatings are applied to the welds. Any welds that have not been previously verified as leak free will need to have coatings removed prior to the leak testing.
Be warned that if this is not done correctly, serious damage/injury can result. Ensure that the method and it's application is pre- approved and inspected by all applicable engineering, supervision and safety department personnel. Do not attempt this unless you are positive that appropriate and redundant safety precautions are in place and you are willing to accept responsibility for the work.
You can check Inspection Trends for a reference to an ASTM specification on the subject of leak testing. I believe it was the Summer or Spring issue of the publication.
All these tests will be in open atmosphere. The ductwork will not be sealed. I would be directing high pressure air at a seam in an attempt to force it through any path that it can find from one side of the joint to the other.
Any thoughts on that?
This will only find large leaks, and is a BS method of "Testing"...
I can't speak for the testing of duct work, but many years ago in the oil and gas industry the diesel test (which is a penetrating medium of sorts) was common for testing for leaks on storage tanks. I always used dye penetrant developer on the opposite face to detect any diesel that may find it's way through. The downside is the clean-up. Tim makes some excellent points about using a low pressure air test and a solution that will form bubbles such as soapy water, 409 cleaner, or a professional product like Bubble Up.
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