The detection of leakage or leak test is a discipline that is part of control techniques to measure and locate the amount of leaking gas, over a given time interval, a slot, a porosity, or a solder microcrack, or else by a connection comprising gaskets. The leak test is a non-destructive examination and it is defined as follows: “Test carried out with the aim of verifying the conformity of materials or components with respect to specific requirements, by calling on techniques affecting neither characteristics nor performance”. This document aims to describe our current technical knowledge in the field of pneumatic leak testing and measurement. It is aimed more particularly at control technicians at the end of the production line. Sectors of application of leak detection Historically, the best-equipped industries in this production phase are those which produce items of high intrinsic danger, or of high technological value. We can therefore make a list of this first “generation” of companies where this need was felt from the start:

  • Aerospace
  • Biomedical
  • Military Navy
  • Pharmaceutical
  • Gas
  • Components for liquid fuels

It was only between the 1980s and 1990s that a campaign to extend these controls to a wider range of products began. Around this time we began to understand that this type of control could be extended, with many benefits, also to non-dangerous products in the event of a leak. If, for example, small oil leaks in engines or transmissions were considered acceptable in the 70s and 80s, by the 90s a small defect of this type already meant nonconformity by the end customer. By applying this principle of technical availability with relatively contained time and costs, this control methodology has spread and continues to spread. It is therefore currently impossible to define a complete list of industries for which this leak test is considered “necessary”, and we can generalize by saying that any product which must contain gases or liquids can benefit from this control. Types of leak detection By leak detection or spark leak testing, we mean a process capable of checking the pneumatic tightness of a product. Let’s make a distinction between two types of leak testing equipment : Verification systems, with operator and location of the leak point. Types of leak testing

  • Water control with pressurized part (visual control.
  • Check with soapy water (visual check).
  • Control with reagents and UV lamps (visual control).
  • Control with pressurized gas (Helium) (mass spectrometer).
  • Check with pressurized hot air (visual check with IR).
  • Dielectric variation control on plastic parts (high voltage ionic system).

Automatic systems with Good/Reject indication and leakage value.

  • Control by measuring the flow rate in the pressurized room.
  • Control by differential pressure drop between the control part and a reference part.
  • Control by the pressure drop in the pressurized room.
  • Control by “recovery” of the increase in pressure under the bell.

While it is true that the first type of equipment constitutes an irreplaceable statistical and offline control area, they also make it possible to locate very small leaks in visual mode, the devices of the second category constitute the effective barrier at the end of the process. They also make it possible to monitor any qualitative drifts over time, if applied to all production. Given the obviousness of the operation of the devices of the first category, we will not dwell on a detailed technical description. Consider only that systems based on mass spectrometers (Helium sniffers), while expensive both in terms of installation and use, are at the pinnacle of leak detection compared to any of the systems. On the contrary, water, soap or reagent systems allow the detection of very small leaks at a ridiculous cost, they cannot be automated and are therefore subject to interpretation by the operator, which can generate errors in judgment.