Principle
When fluid (liquid or gas) sprays out from the leak of the valve, ultrasonic signals are generated. Ultrasonic leak detectors can capture these ultrasonic signals in a specific frequency range to detect whether the valve is leaking. This method is based on the propagation characteristics of ultrasonic waves in different media. Even if the leakage is small, it can generate detectable ultrasonic signals. Therefore, it has high sensitivity and detection accuracy, and can be detected without touching the valve. It is suitable for various complex field environments.
Operation steps
Instrument settings
Turn on the ultrasonic leak detector and set the appropriate detection frequency range and sensitivity parameters according to factors such as the type, size and working medium of the valve. Different valves and leakage conditions may require different detection parameters. Generally speaking, the default settings of the instrument can meet the detection needs of most conventional valves, but for some special valves or complex working conditions, appropriate adjustments may be required.
For example, for a large valve with a high working pressure and a fast medium flow rate, the detection frequency range may need to be set slightly higher to improve the ability to capture ultrasonic signals generated by high-speed leakage; for a small valve with a possible small leak, the sensitivity needs to be increased to more accurately detect weak ultrasonic signals.
Detection operation
Place the sensor of the ultrasonic leak detector close to the valve surface, and keep the distance between the sensor and the valve within the appropriate detection range. Generally speaking, the distance between the sensor and the valve surface should be determined according to the instrument's instructions and actual experience, usually between a few centimeters and tens of centimeters.
Slowly move the sensor along the outer surface of the valve to fully scan all parts of the valve, including the valve stem, valve body, sealing surface, and connection parts. During the movement, pay attention to the signal strength indication and sound prompts on the instrument's display. If there is a leak in the valve, when the sensor passes the leak location, the instrument will detect the ultrasonic signal and display the corresponding signal strength and frequency information. At the same time, the instrument may sound an alarm to remind the operator to find the leak.
For some situations where it is difficult to determine the leak location, multi-point detection and comparative analysis methods can be used. Perform multiple tests at different locations around the valve, record the ultrasonic signal characteristics of each location, and then compare and analyze these data to find the locations with the strongest signal strength or specific characteristics. These locations are likely to be the leak points.
Leakage assessment
Based on the information such as signal strength and frequency detected by the ultrasonic leak detector, combined with actual experience and relevant standards, the leakage degree of the valve is evaluated. Generally speaking, the stronger the signal strength, the more serious the leak. However, the signal strength alone cannot completely and accurately determine the size of the leak. Other factors need to be considered, such as the nature, pressure, temperature, and structure of the leaking medium.
For example, for ultrasonic signals of the same strength, the signal frequency generated by gas leakage may be higher than that of liquid leakage, because the flow rate of gas is usually faster than that of liquid. In addition, the structure of some valves may cause changes in the propagation and attenuation characteristics of the leakage signal, thereby affecting the accurate judgment of the leakage degree. Therefore, when conducting a leak assessment, it is necessary to comprehensively consider a variety of factors and analyze them in combination with the actual situation.
Application scenarios
Ultrasonic leak detection tests are widely used for valve leak detection in various industrial environments, especially for complex pipeline systems and inaccessible valves. For example, in large-scale production facilities of petrochemical enterprises, pipelines are crisscrossed, valves are numerous and widely distributed, and some valves may be located at high places or in narrow spaces, and traditional detection methods may be difficult to implement. At this time, the use of ultrasonic leak detectors can quickly detect whether there is a leak in the valve without disassembling the valve and stopping production, timely discover potential safety hazards, and improve production efficiency and safety. In the power industry, ultrasonic leak tests are often used to regularly inspect valves in the steam piping system of power plants to ensure the sealing performance of the steam system and prevent energy loss and damage to equipment. In addition, in some places with high environmental requirements, such as pharmaceutical factories and food processing plants, ultrasonic leak tests can help detect tiny leaks in valves to avoid affecting product quality and meet strict hygiene and environmental standards.
