About ultrasonic leakage detection

The LeekSeek group uses the most advanced ultrasonic equipment available and continuously looks for improved methods and technology in detecting leakages. Customers are often amazed by how ultrasonics can pick up leakages that are not only inaudible but come from inaccessible areas or overhead air-lines. So how does it work? As the name implies ultrasonic leak detectors detect the ultrasonic sound of the leak. You are probably familiar with the hissing sound a large leakage makes. Smaller leaks also emit sound, however the frequency is too high for our ears to detect it. By a process called heterodyning, the detector translates the ultrasonic hissing sound to a lower frequency where it can be heard through headphones and direct you to the source. As you get closer, the sound gets louder. If you decrease the sensitivity as you close in on the leakage it will pinpoint its exact location. Some leakages can be heard several meters away, therefore direct access to the leakage is not always necessary. As long as the leak is turbulent, there will be enough sound to be detected ultrasonically.

Ultrasonics can detect pinhole leakages with a pressure as low as 0.5 bar, however, the more pressure behind the leak, the more turbulence there will be and the easier it becomes to locate. The LeekSeek members use detectors that are most sensitive to sounds around 40kHz, which is twice the frequency of the best human hearing. Any turbulent gas will generate ultrasound when it leaks, therefore it does not matter what gas you are testing. The detector will discover leakages of air, nitrogen, new or old refrigerants, even air as it rushes into a system under vacuum. The detectors the LeekSeek group uses are so sensitive that they will detect the blink of the human eye, but again it is not gas specific. For example, a leak test can be done in an enclosed area, which is saturated with refrigerant, and the only indication the detector will give you is the sound of the leak. As the detector is focused on a specific band of sound, wind noise, voices, traffic and most normal operational sounds will not register. You can actually yell directly into the sensor and hear nothing. This means that leakage detection can be made during production hours which is a prerequisite for successful leakage detection as many leakages are production related. Leakage's in many cylinders, valves or other pneumatic equipment are multi-positional and require detection over their full running cycles to appear. For the same reason, leakage detection done after production hours or in the weekend, only detects a fraction of the existing leakages.

Sensitivity

Many questions we have from clients relate to what sensitivity a detector has. The principle of operation of the detecting equipment we use are based on turbulent flow. For a leak to appear there must be an opening in the system that carries a gas or a fluid. Normally, these openings are not clean smooth holes, but passages through cracks with many jagged edges and internal chambers. Fluid or gas escaping through an "orifice" like this is forced into turbulence (random circular-like motions). Turbulent flow has a high content of ultrasound. This is sound that is above the human hearing range, but can be heard with an ultrasonic detector and traced to its source. It is important to remember that a piece of straight tubing connected to a gas supply and left free to exhaust into the atmosphere will not generate sound if the volume of gas through it is such that turbulence does not take place. Yet for the same flow, an opening of 0.1 mm can generate enough sound to be heard several meters away.

The intensity of sound generated by a leakage is a very complex function of the viscosity, the temperature, the speed the fluid is moving, the Raynolds number, the pressure differential across the leak, and the physical dimensions and characteristics of the orifice. This is why it is possible for a smaller leakage to generate more sound than a large one. Ultrasonic leak detectors "hear" leakages, therefore the sensitivity can not be accurately stated in terms of cc/sec, parts of a million or grams per year. The proper specification for these types of detectors is decibels. The amount of sound pressure created by the leakage will determine its ability to be detected ultrasonically.

Realistically, an ultrasonic detector will detect most of the leakages you encounter in an industrial environment. It is the only instrument that will pinpoint a vacuum leak, or detect any pressurized gas in any system. It is also more accurate for detecting larger leakages because its sensor will not become saturated or false alarm from the presence of gas in the atmosphere. Because ultrasonic detectors do not "sniff" out the gas, they can easily locate leakages even under windy conditions.

A reporting system - Essential for leakage detection

A successful leakage detection program is dependent on an effective reporting system. It should keep your company firmly on a documented track to reduced leakage levels. Therefore it should be just as focused on the identification of leakages as of their causes. Correctly implemented and supported it will provide vital data on where the leakages are reoccurring, which components and equipment cause repeated problems, which workplaces need closer attention, appropriate service interval suggestions etc. Without a reporting system, people responsible for documentation and repair you will be far from achieving the results possible. Due to the nature and cost of leakages a poorly managed system can be of great economic consequence.

All members of the LeekSeek group use the same system of identification and reporting of leakages which contains the following elements.

1. Establish a system for workplace identification.
For easy repair and overview it is important that the located leakages are tagged or labeled with a number or identification that allows tracking.



2. Tagging or labeling
The LeekSeek group uses a tagging system that indicates the degree of leakage.
Grade 1 – Blue tag indicates a leakage that is not audible even in a quiet environment
Grade 2 - Yellow indicates a leakage that is audible in a quiet environment.
Grade 3 - Red tag indicates a severe leakage requiring immediate attention.
Each tag contains the following information. Workplace identification number, tag number, date of repair, date for after-control and responsible person. Each tag also represents a volume that is automatically calculated once the leakage is entered into the web based LeekSeek™ system.

The number or classification of the leakage is used primarily as a priority guide when planning repairs and can only serve as a general guideline about the total leakage volume. A leakage of 1 mm is classified as a leakage that requires immediate attention just as a 6 mm leakage is. However the number of tags and their classification gives you a good idea of the state of the system and serves as a benchmark for continued leakage detection.