The integral leaktest with helium pressure in the volume around the tubes and vacuum in the tubes

This test is sometimes necessary, when the volume around the tubes has had a helium filling in the past, for example for a leaktest with the sniffer probe. The changes in test conditions are decribed. Also the calculations of the leakrate according to pressure changes are discussed and the possibility of cost reduction by reducing the helium concentration as a result of pressure increase is pointed out.