Innovative Reliability Excellence in Helium Gas Leak Testing by Vacuum Method

In Helium gas leak testing, reliability is an imperative factor and improving this is challenging. One of our innovative experiences is shared in the form of a case study in this paper. Heat exchanger for a process plant shall have to be Helium leak tested by vacuum method for the Quality review of weld joints between ring header and straight tubes. Upon conducting the test, all open ends of other side of tubes were sealed using plugs and vacuum was created. A polythene hood covering all the weld joints of ring header and tubes was sprayed with Helium. Helium from hood passed out and moved up due to its high diffusivity. The diffused Helium could find leak paths in the open ends of the tubes with in the seal plug system and entered into the vacuum side. Being a small tube, that too, many in numbers, with no inner diameter control and close pitched condition, complete Helium tightness of seal plugs could not be thrived. Also, permeation of Helium through rubber seal of sealing plugs could not be avoided. Due to this, substantial amount of Helium went into vacuum system when test joints were sprayed with Helium and these were revealed as spurious signals. In order to resolve this, a dummy polythene envelope of gaseous Nitrogen was provided covering all other ends of tubes, including seal plugs. This nitrogen blanket has avoided spurious signals and improved the test reliability. Thus, Response time aspect of leak tests was suitably deployed to obtain reliable test results in a typical Industrial Application by combating the specious signals effectively.