Leak testing of semi-welded plate heat exchangers can accurately verify leak rates and, thereby, the safety of the exchanger. To confidently detect leakage and meet leak rates required by law, a gas that has molecules smaller than water and refrigerants should be utilized for leak testing. The clear choice of gas for testing leaks, therefore, is helium.
Using helium during testing for safety and performance has advantages over traditional hydraulic and nitrogen testing. While hydraulic or nitrogen tests may be adequate, they are not conclusive to the point of certainty — or particularly safe, in some cases. Exposing semi-welded plate heat exchangers to a helium leak test is a tougher test than nitrogen or water due to the helium molecules’ smaller size and capacity to reveal much smaller leaks during testing.
This method of testing validates the plates’ operation and performance to demonstrate the industrial refrigeration system will have a safe and reliable semi-welded plate heat exchanger. Helium leak testing can be used whether the semi-welded plate heat exchanger has new or retrofit plates.
Another reason to avoid using nitrogen to pressure test your semi-welded plate heat exchangers is the inherent risk in compressing this particular gas at high pressure. The forces released if the construction breaks are dangerous and can jeopardize employees and the testing facility. From a health-and-safety perspective, the use of any gases to complete pressure testing is undesirable without additional safety precautions such as testing inside a sealed chamber designed for such purposes.
For semi-welded heat exchanger plates, helium leak testing is a tougher test than nitrogen or water due to the helium molecules’ smaller size and capacity to detect smaller leaks during testing.
Helium leak testing can uncover potential material cracks in semi-welded heat exchanger plates that may be missed during manual and visual checks.
It is recommended to combine aspects of helium and hydraulic methods when performing strength and leak tests on your semi-welded plate heat exchanger. This results in a three-step testing program:
- Perform a hydraulic strength test to reduce the health-and-safety risk.
- Conduct an internal helium leak test to verify the sealing capabilities of the ring and diagonal gasket to avoid product contamination.
- Execute an external helium leak test to verify sealing capability to its surroundings.
Helium testing is fully automated at some assembly facilities. This allows 100 percent of the semi-welded heat exchanger plates to be helium leak tested in factory conditions — multiple times — to document correct gasket sealing and the tightness of cassette.
Semi-welded heat exchanger plates are helium leak tested in factory conditions multiple times to document correct gasket sealing and cassette tightness.
In such a program, the first test begins with a helium-leak chamber. Every cassette is inserted in the chamber to check the tightness in order to detect any cracks or leakage through the plate surface and welding of the plate. Each test takes approximately 30 to 35 sec. The test can be used to determine whether all of the semi-welded plates are tight enough to be passed on to the assembly line or delivered to users needing replacement plates or plate packs to extend an existing the heat exchanger.
The helium leak chamber can help detect potential material cracks in the plate that might be missed during manual and visual checks. (Manual checks occur when the operator of the machine, after manufacturing the plate, examines the cassettes to find imperfections in the body and design.) Visual checks are at high risk of missing cracks inside the plate’s material, which may result in contamination or leakage problems after some period of operation due to fatigue. These cracks are invisible — even for the best eyes.
Another issue that stems from visual checks is the human factor. Operators are responsible for checking hundreds of cassettes of varying sizes. As a result, mistakes can, and often do, occur. It is only natural that the helium leak-chamber test can deliver more accurate results.
Helium leak testing under factory conditions allows a manufacturer to document the correct gasket sealing and the tightness of cassette.
After completing the helium leak test of the single cassettes, the cassettes are passed to the assembly site, where gaskets are mounted and, eventually, the plate pack is built into a frame. A hydraulic strength test then is performed according to specified design codes (PED or ASME). Once completed, the semi-welded plate heat exchanger is dehydrated under vacuum and then ready for the second and third helium leak tests. The internal leak test is performed via accumulation passing the ring gasket and gasket diagonal. This leak test will ensure that there is no contamination between the two fluids running on each side of the plate. The external helium leak test also is performed as an accumulated leak test to verify the gasket-sealing capability to the outside.
Helium testing, preferably through both internal and external checks, can help ensure the safety and reliability of industrial refrigeration systems while also delivering comfort in knowing helium tested semi-welded plate heat exchangers will boost performance and help systems meet regional guidelines. PC