Overpressure Leak Testing
Due to the fact that health, safety and environmental aspects are becoming more and more important in any industry, there is a constantly growing need for industrial leak testing. Selecting the best leak test method is an economic decision that balances the cost of meeting the leak test specifications within the conditions and requirements of production. While leak testing may look to be a simple procedure, the process involves a combination of both science and skill. The test operator must ensure the equipment is functioning properly (i.e. calibration of test equipment, tracer gas pollution in test environment etc.), and the process is highly dependent upon the operator’s experience.
ITIS can provide you the following techniques for overpressure leak testing:
- Tracer gas sniffer test method
With the overpressure method, the to be examined part is filled with a tracer gas or tracer gas mixture. The pressure inside the part is increased to the desired rate so as to create a differential in pressure. Laws of physics then state that particles under higher pressure (test object) will try to move to the lower pressure (outside environment of the object). The exterior of the part under examination is then scanned by using a probe attached to a leak detector. Due to the innate properties of the test gas it readily migrates throughout the system, and in its attempt to escape penetrates any imperfections, including: defective welds (cracks, pin holes, incomplete welds, porosity etc.), flawed or missing gaskets or any other defect.
Helium, hydrogen and halogens are typical tracer gases.The used detector probe is in most cases called a ‘sniffer’, a needle probe continuously taking gas samples. The sniffer probe technique is very sensitive but has its limits due to the amount of helium present in the atmosphere (5 ppm) which can influence accuracy. The maximum sensitivity achievable with this test method is approximately 1×10-6 mbar·l·s-1.
- Hood test method
The hood method or accumulation test is an integral test method and is more sensitive than the direct sniffer probe method. This method is also used to detect defective welds, flawed or missing gaskets, permeation or any other defect. All to be tested parts will be sealed with tape to create an isolated volume or hood. The system or parts are then pressurized with a test gas (mixture). The volumes are sampled during a set hold time to determine a potential raise of test gas concentration (ppm). An increase of test gas concentration in the volume during the hold time can be calculated to an actual leak rate of each part.
- Ultrasonic test method
Ultrasonic leak testing can often be carried out relatively simple and is recognized as a decisive strategic priority. When used as a first step for assigning preventive maintenance on all of your plant’s assets, the technology can provide valuable insight about where a problem is occurring. While ultrasound leak detection is an excellent way to determine where a plant is losing steam or compressed air, its ability to pinpoint where preventive maintenance is necessary is of equal value.
- Acoustic Emission test method
Acoustic emission (AE) is a very sensitive test method and one transducer can adequately monitor a large area or structure. It is vital that there is a degree of confidence (resulting from experience) in the method as the test is dynamic and cannot be verified by repetition.
When a structure is subjected to an external stimulus (change in pressure, load or temperature), localized sources trigger the release of energy in the form of stress waves, which propagate to the surface and are recorded by sensors. With the right equipment and setup, motions on the order of picometers (10-12 m) can be identified.Because of the many different situations this test method can be applied to, it sees extensive use in situations such as: the detection of active corrosion in the bottom of aboveground storage tanks, detecting creep damage in high energy piping (HEP) systems, pressure vessel inspection and leak detection in general.
LDAR (Leak Detection And Repair) monitoring programs are intended to ensure that fugitive gas emissions are identified and eliminated, and to prevent air pollution and protection of the environment.Research has determined that leaking equipment, such as valves, pumps and connectors, are the largest source of emissions of volatile organic compounds (VOC’s) and volatile hazardous air pollutants (VHAP’s) in petroleum refineries and chemical manufacturing facilities.
Emission reduction from implementing an LDAR program potentially reduces product losses, increases safety for workers and operators, decreases exposure to the surrounding community, reduces emissions fees and helps facilities avoid enforcement actions.Our test engineers are able to help our clients to develop LDAR programs.
Prior to developing a written LDAR program plan, all applicable regulations should be reviewed to determine and ensure compliance with the most stringent requirements.