The system in pressure type helium leak test refers to the immediate zone surrounding the test location on the low pressure side. Normally, polythene envelopes are provided on low pressure side covering a part of the test zone. Leaking helium from the high pressure side will be collected for sufficient time and a sample of the collected helium will be sniffed by a probe pierced into the envelope. In case of leaks, indication will be observed in the leak metre. For exact quantification of actual leak rate, the helium collection time before sniffing and the envelope volume are the two factors to be considered as they have an effect on leak signal pick up. In the new methodology of system calibration, before filling the helium into the vessel, known amount of helium is allowed into the representative envelope for known time using an indigenously developed capillary type reference leak. Then, the sniffer is pierced into the envelope and the leak metre reading is recorded. The ratio between actual rate of reference capillary leak and the leak metre reading is found and this ratio is the calibration factor for pressure type helium leak test. During the actual test, after accumulation of helium in the envelope, the sniffer probe is pierced into the envelopes and the leak metre readings are recorded for each and every envelope. These readings are multiplied with calibration factor for obtaining the actual leak rates and thus the leaks are quantified.

This new methodology of system calibration and leak rate quantification have been successfully demonstrated for pressure type tests in some of the heat exchangers to the satisfaction of third party inspectors and customers.