In the vacuum type helium leak testing, for faster generation of test vacuum inside the vessel and for retaining the vacuum after isolation of pump while spraying the helium, the components, materials and the joints in the test rig (other than the items undergoing leak test) have to be sufficiently leak tight. A systematic procedure has been successfully established to achieve this purpose and the quality of the dummy joints and test connections is ensured before starting of the actual test. This helps in faster test completion besides giving unambiguous test results.

The hoods made for helium spray or helium accumulation have to be sufficiently air tight for better sensitivity. For this, quick rust removing compounds are useful to obtain the clean surfaces for sticking the polythene sheets of helium hoods.

For leak location identification in tube to tube sheet welds of heat exchangers, segmentation procedure for dividing the test zone has been modified to obtain the advantage of minimisation of spurious leak signals. Further, for faster detection of leaks in such segmentation operations, the RESPONSE TIME during testing has been IMPROVED by shifting the location of the detection port.

The percentage concentration of helium in test hoods is a variable quantity and the actual value of the same really affects the test reliability in vacuum type helium tests. A new technique has been successfully established and an experimental set up has been rigged up to calculate the exact percentage concentration of helium in test hoods.

Normally, tube to tube sheet welds of heat exchangers are helium leak tested prior to tube expansion by creating vacuum on the rear side of the weld in the annular space and by spraying helium on the welds are not accessible for vacuum creation and hence leak testing of welds by normal method is not possible. A new method of helium leak testing - BOMBING - has been successfully developed for carrying out helium leak testing of tube to tube sheet welds after completion of tube expansion. Using this method, a fool-proof calibration procedure and trial testing of few tube welds after expansion have been demonstrated to the satisfaction of the customer. Further, this method can be conveniently adaptable for the exclusive examination (by leak rate measurement) of tube sheet welds during the planned inservice check programmes of tube sides of heat exchangers.

Vacuum type helium leak testing has been introduced for faster test completion in place of pressure type based on successful comparison mock ups for one of the header like assembly. This has resulted in the considerable reduction in the total manufacturing cycle time of the particular assembly.

Also, for the first time a proven leak rate quantification procedure has been demonstrated for pressure type helium leak tests. Based on this, both leak location identification and leak rate measurement are possible with pressure tests also.

Vacuum jackets have been introduced successfully for the critical multi plane plate weld joints.

TOP MANAGEMENT SUPPORT AND TEAM WORK have made these advancements possible and as a result of this, BHEL, TRICHY enjoys the benefit of TOTAL CAPABILITY ACCOMPLISHMENT in the field of helium leak testing.