The Importance of Leak Detection

One example of the importance of using leak detection systems is the need to monitor systems containing toxic and hazardous materials, where the leakage rate must not exceed the standard. If it does, it could adversely affect human health, harm the environment, and even impact the system's effective operation.

Leak detection has three key factors:

1. Does a leak exist?
2. What is the extent of the leak?
3. Where is the leak located?

Regarding whether a system has a leak, it should be noted that no system is completely leak-proof. A system is deemed leak-free if the leakage rate remains below the permissible limit. Therefore, during the leak detection process, it is crucial to know the allowable leak rate for the specific system.

It’s important to note that various techniques exist for leak detection, but no single method can be applied universally to all systems. Each technique is suitable for specific leakage rates or equipment types.

In most cases, the precise amount of leakage is not critical; what matters is ensuring that the total system leakage does not exceed the allowable limit for a specific application. If it does, the leak location must be identified and rectified.

Leaks in equipment can arise for several reasons, particularly in closed systems. Leaks often occur due to connections, weld areas, unintended gaps, holes, porosity in the walls, or thermal expansion.

Leak detection should be considered a part of quality control for the equipment in question. Ideally, it should be a non-destructive test with no impact on the environment or the operator.

Additionally, since no connection can achieve an absolute zero leak rate, specific leakage rates are defined for each connection and material. These standards must be observed during system design and usage, ensuring the correct connection type is selected based on working pressure and application.

Leak Detection Methods

Some leak detection methods are based on physical phenomena that occur during leakage. For example, the ultrasonic method detects the vibrations and noise generated when fluid escapes through a leak. The sensitivity of this method is around 10^-2 mbar.l/s. Although methods like the soap and water technique can achieve a precision of up to 10^-4 mbar.l/s, their accuracy heavily depends on the maximum fluid pressure, making these ideal figures difficult to achieve in practice.

Another method involves detecting temperature changes caused by fluid leakage, which can be measured with thermal cameras to identify the leak location. Additionally, pressure changes in the system due to fluid escape, known as pneumatic or hydrostatic testing, are common in the industry. However, like the ultrasonic method, the sensitivity of this technique is strongly influenced by fluid pressure and environmental conditions, making high precision challenging.

Although these methods are quick and inexpensive, and can sometimes locate the leak, they have significant limitations. They cannot accurately measure the exact leakage rate. For high-precision leak measurements and detection of the smallest leaks, methods that precisely measure the fluid escaping from the leak should be used. One of the most important techniques in this field is the tracer gas method.

Tracer Gas Method

The tracer gas method is based on the diffusion of the gas through the leak, driven by the pressure difference on either side of the surface. The gas escaping from the leak is analyzed with special, high-precision equipment to directly measure the amount of gas escaping. The tracer gas used must meet the following criteria:

• It should be measurable with high precision.
• It must be inert, non-explosive, and inexpensive.
• It should be present in very low concentrations in the environment to ensure measurement accuracy is not compromised.
• It must be easily evacuable through pumping, leaving no residue in the system.

In most cases, helium is used as the tracer gas. Therefore, leakage rates are typically expressed based on the helium standard leakage rate (He STD) when the pressure difference between the vacuum and the external environment is 1 bar.

Helium’s small molecular size allows it to pass through extremely fine holes, making it possible to detect very small leaks. Moreover, since the speed of helium molecules is three times faster than air molecules, the amount of gas escaping through leaks is three times greater compared to regular air.

Below is a table comparing the achievable precision of helium leak detection with other methods based on the ASME standard.

Helium Leak Detection Methods

Spray Method

The spray method is one of eight major methods to test for leaks. It is effective at finding small leak points in a test object. To perform the test, the inside of the test object is first evacuated. Then, helium gas is sprayed onto the outside of the object. If there is a leak, the helium gas will leak into the test object and can be detected.

Vacuum Hood Method

The vacuum hood method is another method used to detect leaks. It is best suited for quantifying total leakage from a test object. To perform the test, the test object is placed inside a vacuum hood. The hood is then evacuated, and the rate at which the pressure inside the hood rises is measured. This rate can be used to calculate the total leakage from the test object.

Sniffer Method

The sniffer method is a leak detection technique that involves using a specialized instrument called a sniffer to detect the presence of helium gas. The sniffer is placed near the suspected leak point and is able to detect even small amounts of helium gas. This method is particularly effective for detecting leaks in large or complex systems.

Pressure Accumulation Method

The Pressure Accumulation Method is a leak detection technique used to identify leaks in sealed containers or systems. It involves pressurizing the container or system with a gas and then monitoring the pressure over time. If there is a leak, the pressure will gradually decrease as the gas escapes. This method is particularly effective for detecting slow leaks that may be difficult to identify using other methods.

Suction Cup Method

The Suction Cup Method is a leak detection technique used to identify leaks in large, flat surfaces. It involves placing a suction cup over the suspected leak point and then applying a vacuum. If there is a leak, the suction cup will not be able to adhere to the surface and will be pulled away. This method is particularly effective for detecting leaks in large tanks or vessels.

Bell Jar Method

The Bell Jar Method is a leak detection technique used to identify leaks in small, irregularly shaped objects. It involves placing the object inside a bell jar and then creating a vacuum inside the jar. If there is a leak, the object will not be able to hold a vacuum and will gradually lose pressure. This method is particularly effective for detecting leaks in delicate or fragile objects.

Bombing Method

The Bombing Method is a leak detection technique used to identify leaks in large, sealed systems. It involves pressurizing the system to a very high pressure with helium gas and then monitoring the pressure over time. If there is a leak, the helium gas will escape, causing the pressure to gradually decrease. This method is particularly effective for detecting large leaks in systems that are difficult to inspect using other methods.

Arbitrary Pressure Method

The Arbitrary Pressure Method is a leak detection technique that involves pressurizing a system with helium gas to an arbitrary pressure, which is typically lower than the maximum operating pressure of the system. This method is often used in conjunction with other leak detection techniques, such as the sniffer method or the vacuum hood method, to identify and quantify leaks in a variety of systems.

Helitek is the pioneer in providing helium leak detection services. For more information on our services in various areas such as underground pipelines, heat exchangers, cold boxes, power systems, and more, please contact us.