Cooling Channel Tightness Test

[Mike048]

Hello together,

in our line, we plan test cooling channel tightness with air as its easier than using water. However, I would like to ask:
1) Pros and Cons between testing with air and water?
2) Can an OK tested part (air test) become untight once channel is operated with water? Is there a good formula to define the the allowed leakage rate (l/min)?

Thanks.

 

[EdStainless]

An air test can be dangerous if a part fails, there is high stored energy.
Air test is much more sensitive than with water (perhaps by 100x).
With air you don't need high pressure.
We used to test at 150psi and ran some tests at 50psi, 150psi and 450psi. The results were nearly identical, but testing was more difficult at higher pressure.
Our acceptance was that parts were under water and we allowed no visible bubble in 3 min.
It is difficult to air test by flow rate or pressure decay because slight temperature changes can swamp the leak.
I have seen parts tested as pressure differential. Two parts are connected and simultaneously pressurized, after a short stabilization they are isolated from the source and each other. You are assuming that the temperature effects are the same for both. You can measure the pressure difference between them with a very sensitive differential pressure gauge (maybe sensitive to 0.01psi). usually a settling time of a 5sec and a measurement time of 10-15s will be sufficient. If one part drops in pressure you assume that it has a leak. You do need a total pressure sensor in case they both leak.
Regrettably you will have to adjust the sensitivity by trial and error.

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P.E. Metallurgy