Tech Showcase: Leak Testing Diversity
In a basic example of tracer gas leak testing, a tracer gas is introduced to one side of the test subject. Then a differential pressure is applied to the test subject, with the higher pressure at the tracer gas side. An instrument, such as a mass spectrometer, is then applied to the lower-pressure side of the test subject to detect the presence of the tracer gas. The gases used in this method are typically helium, hydrogen and refrigerant halides (R-12, R-22).
Tracer gas leak testing is performed in many industries, including automotive, beverage and medical device. Tracer gas leak testing is the most effective leak testing method, with the use of a mass spectrometer and the radioisotope method having the highest leak test sensitivity. Leak sensing times can be short, often ranging from 1 to 8 seconds, and test time does not usually increase greatly with part volume. With this method, testing can be automated, and tests can be performed at various temperatures. However, while some gases used in this method are inexpensive, the equipment is more expensive than that of other leak testing methods; furthermore, it will require calibration and usually special cleaning. There are safety issues as well. While gases such as helium do not pose health risks, some gases are hazardous, and concerns such as toxicity, radioactivity or flammability must be addressed.
Bubble emission leak testing has two basic techniques: immersion leak testing and film solution leak testing. In immersion leak testing, an internally pressurized test subject is immersed in a test medium. The subject stays in the test medium for a period of time and is then examined for bubbles.
In film solution leak testing, an internally pressurized test subject is covered with a liquid film solution that allows the formation of visually discernable bubbles. Bubble emission leak testing can be used with test subjects such as hydraulic and pneumatic tanks, tubing and pipe assemblies, and valves and valve seats. The method should be used when operator subjectivity can be tolerated and when allowable leakage can be large. While the technique is easy to learn and perform and is inexpensive, it is not quantitative and has limited leak-detecting sensitivity. Furthermore, it is time consuming and brings with it some safety concerns, such as water contamination and the risk of electric shock or fire.
Air leak testing manually or automatically applies regulated air pressure or vacuum to the test subject. Leakage is detected by loss of pressure or vacuum (pressure/vacuum decay) or the need to add air to compensate for air escaping from the subject. A range of devices can be used to detect pressure loss, from simple pressure gages and pressure switches, to complex electronic pressure transducers that report small pressure changes to electronic instrumentation. Likewise, a range of devices can be used for detecting flow, from simple water manometers or variable area flowmeters, to complex electronic transducers that report small flow changes to electronic instrumentation.
Air leak testing is used in the automotive and other industries for testing parts that will operate in service with liquid, gas or vacuum. Typically, air leak testing is fast, repeatable and no postcleaning is necessary. However, the method does not provide leak location and has low sensitivity. There also are safety issues involved when used at high pressures.
What follows are a number of leak test offerings for today’s nondestructive testing applications.
The instrument is appropriate for quality helium leak detection requirements in a range of applications including semiconductor, automotive component testing, refrigeration, and air-conditioning assemblies and subassemblies.
Air-to-air cycling of the custom systems is automatic; components are placed in a vacuum chamber, charged with helium and the chamber is evacuated. A mass spectrometer-based helium leak detector is used to measure a total leak rate for the components to check all leak points to guarantee product quality. Pump systems are sized to evacuate both chamber and test part to a suitable pressure within a short period of time to meet the requirements of a desired machine cycle time. The leak detector used is the Heliot 700 with sensitivity to detect helium leaks as small as 1 x 10E-12 mbar-liters/second. The factory automation interface with the system can be engineered and supplied by Ulvac as well. Each system is equipped with a modem link so that system software troubleshooting can be done remotely by a telephone to the Ulvac service center, useful in enabling remote assistance for faultfinding and completing software changes with minimal delays.
The leak testing systems can be used to test high-pressure components at their operational pressures up to 100,000 psi. This allows companies to find leaks on high-pressure components in-house.
Standard and custom system configurations are available for a variety of applications. Pressure control modules are available to handle measurements from vacuum to ultra high-pressure.
Testing reports include testing measurement data, graphs and statistics for QC/QA monitoring.
The integration of the company’s standard pressure generation and control modules allows cost-effective solutions for a variety of applications in various markets, such as automotive, aerospace and medical.
New features include an operator-selectable cumulative leak site integration feature to distinguish whether each individual leak site is an accept or a reject, and to determine if the accumulated leak measurements exceeds the specified leak reject limit; parts can either reject on one leak site or the accumulation of multiple sites. Other features include built-in gross leak test capability to eliminate tracer gas contamination; up to 10 part-specific recipes, each with up to 10 leak sites, with user configurable dwell time at each site; barcode scanner input; serial printer output; remote monitoring over an Ethernet connection; and PLC control allowing for flexible configuration.
The system can be integrated with the company’s MD-490S Real Sniffer portable dry industrial helium leak detector for tracer gas charging of products prior to fine leak testing. Gas recovery and mixing options also are offered to create a completely integrated gas handling and test system.
Complementing the ME001 Series, the ME01 and ML001 connectors feature a maximum sealing capacity of 0.510 inch. Additional features include aluminum or stainless steel housings, FDA-approved seals and lubricant, and replaceable size and seal materials. The connectors are chemically cleaned and double bagged for added protection.
The instrument is available with dual USB ports, RS232 serial port and optional Ethernet. It is compatible with the company's test reports and monitoring software. The device talks to a PLC and downloads the leak rate directly into a database to store device history records.
Programming and operation menus are intuitive, and information is displayed via the high-resolution color graphic interface, allowing clear viewing of pressure and flow curves as well as numeric data.
Available with the leak detectors is the Leak Test Data Wizard, a flexible, PC-based data management tool for use with the company's VS instruments. The software provides custom automation of leak test processes ensuring testing uniformity; step-by-step guidance through testing processes; and graphically displayed leak test results that provide individual part test histories or identify trends in high-volume test applications.