Leak Testing Machines

LEAKAGE TEST SYSTEMS DESIGN AND INSTALLATION IN LABORATORIES AND INDUSTRIAL PRODUCTION LINES

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Industrial Leaking Test Systems

Leak testing is applied to determine whether the product is acceptable or unacceptable by measuring how much and in what proportions the liquid or gas passes through the walls of the controlled volume.

The requirement of the test may come from state regulations, as well as environmental factors, human health and safety, product performance and quality. Leakage can be determined by many different industrial leak test methods, which you can find in detail below.

There is always a pressure difference for flow in liquids or gases. Likewise, there must always be a pressure difference between the indoor environment and the external environment for a leak to occur.

As Normtech, we are quite experienced in this area and we are collaborating with worlds leading leak testing company, Innomatec Test- und Sonderanlagen GmbH.

Innomatec, based in Germany, is specialized in leak test, functional test, flow and Helium test applications. The company has both testing devices and turnkey solutions for final customers. In Turkey, Middle East and Africa region, we are able to provide you the expertise and quality of Innomatec in your projects both for leak testing devices and turnkey solutions.

For more info, you can visit Innomatec’s official website.

Or you can visit Normtech and Innomatec collaboration for a brief summary of Innomatec

We have prepared this page to serve as a guide for employees working in process development, production, maintenance, and quality departments, who plan to establish a leakage test system in the industry and need to make improvements to the existing system. We hope you get the most out of it and you can always contact us to exchange more detailed information, to get design, manufacturing, and commissioning support for the system installation.

Finding the Right Leakage Test Method

Step 1: Determination of Output in Leakage Test

The leak test is applied in many different sectors before the product reaches the user or at certain stages of the process. It is generally done to determine one of the following 3 factors.

  1. Whether there is a leak in the product
  2. If necessary, what level of leakage is in the system
  3. Leaking locations

Step 2: Evaluating Product Features and Creating Test Criteria

While determining the leak test method; the first step is to decide which of the objectives listed above is primarily required for the process. Afterwards, the features related to the product should be listed. Among these, the following questions should be answered, so that there will be a certain elimination among test methods.

  1. By which methods and processes are the product joints and leakage points combined or manufactured?
  2. What will be the pressure values and fluid to be used by the end user?
  3. What is the control volume of product?
  4. What is the precision required for the leak test on the product, what are the measurement specifications and criteria?
  5. What are the dimensions of the product, is it possible to take it under a closed volume?
  6. Does the product change shape under the effect of pressure? What material is it made of and what is its elasticity? At the same time, the rate of control volume from product to product may vary.
  7. Is there any problem with the product due to contact with water or oil, or is the water or oil residue undesirable after testing?
  8. Is it necessary to detect leak locations?

As a result of these questions, it will be seen that some test methods are not suitable by themselves.

Step 3: Evaluation of Possibilities for Leakage Testing Process

At this stage, it is possible to determine the most appropriate test method by considering the investment and operating budget, the advantages and disadvantages of sealing test methods, the need for test cycle time, the required test capacity and numbers, test frequency, etc.

As Normtech, we are happy to assist you, our customers, in determining the correct test method, with our experience in leakage testing and test systems. If you need support and more information on which leak test method to use, please contact us.

Comparison of Leak Test Methods
Graph: Comparison of Leakage test methods’ precision
Differential Pressure Decay Test
Graph : Air Leak Test Stages

Leakage Test Technique

Sealing Test Terms

Before we begin to understand the leak testing devices and methods, we would like to give some terminological information. Leakage test methods are also categorized within the framework of this terminology, in other words, both method and device selection should proceed in the light of this information.

Test Part

The product to be tested is the most important factor in determining the test pattern. If you are going to test an automotive part, trying to find the leak amount by using compressed air might be sufficient, on the other hand, for a towel warmer, to immerse the products in water and see if foam comes out is the proper way. Environmental conditions, test medium and test methods are differing from part to part.

Test Medium

Test medium is a term used for test fluid. Leakage tests are basically categorized according to the test medium. If a gas such as hydrogen, helium or air is used as the test fluid, these tests are called the helium leak test or the air tightness test. If liquid is used as a test fluid, they are similarly referred to as Liquid leakage test. Liquid impermeability tests are also generally a category for tests performed with water, oil, or any other liquid.

Test fluid determination is the most critical point of test method and test setup. Environmental conditions and functioning fluid in the product are some of these parameters. Another parameter is the amount of the leak, depending on the size of leak path.

As an important point, depending on the molecular size of the test fluid, the sensitivity of the leakage test varies. Leakage tests with air and other gases are obviously more sensitive than liquid leakage tests and are more preferred if capillary and small leaks are required to be caught. Again, considering the molecular weight, from large to small; can be listed as air, helium and hydrogen. With the smaller molecular weight, the sensitivity also increases.

Also, in the liquid leakage test category, oil molecules are larger than water. Therefore, although water leakage test provides an advantage over oil in terms of sensitivity, oil is preferred instead of water in some applications, as there is a possibility of generating rust on products that come into contact with water. Another advantage of liquid leakage test compared to gases is that they allow the tests to be carried out at higher pressures, in other words, to create high pressure differences safely, due to the fact that the change of volume with pressure is less.

Test Volume (Internal Volume)

The test volume represents the volume in which the test fluid will fill in. It covers the entire volume of connecting hoses, fixture and test piece, starting with the test device. The smaller it is, the higher sensitivity and better reproducibility of the test result. In addition, the cycle time for the test is completed faster. The larger the volume, the greater the time required to fill the volume and bring it to a steady regime.

Test Filling Time

The test fill time is the time it takes to fill the volume to be tested with the test fluid. The time that passes until the test piece reaches the set test pressure level is called the filling time.

Test Stabilization Time

The stabilization time starts after filling time. After the volume to be tested is filled, some fluctuations in air pressure continue to occur (the part indicated by Phase 3 in the picture on the right). In this process, starting the test will cause serious variations, so the system is expected to enter the regime and come to a stable state for a certain period of time. The required test stabilization time can be determined by various repeatability (R&R) studies.

Test Time

It is the last phase of the leak test (figure-1 phase 4). In this process, the result is obtained by measuring the leakage amount. In order for the test result to be healthy, all phases must be as long as necessary.

Leakage Test Methods

There are variety of leakage test applications in the industry. As we mentioned before, deciding on the most accurate leakage test method can be made by considering many parameters that change specific to the product and the process.
The sensitivity of the leakage test methods can be seen comparatively in the adjacent image. Below, we present the common tests and the ones we apply in more detail.

1. Bubble Leak Test by Immersion Method

This method is a very primitive and traditional method compared to others. During this method, the bubbles are observed when the test piece filled with pressurized gas is immersed in water. The larger the size and the more the bubbles, the greater the leak.

This method is useful in finding the leak and in some cases the location of the leak. The water immersion method is very economical compared to other methods. However, for some applications, there are disadvantages in the form of low precision, operator dependance and for some test pieces, difficulty in immersion and drying.

Although the sensitivity of this method is low, better results can be obtained with the following improvements:

Higher pressure ensures that leaks are more visible and the test takes less time.
The detergent added to the water prevents the bubbles coming out of the product from clinging to the product surface by reducing the surface tensions. Bubbles appear easier.
Using smaller molecule gases such as helium instead of air as the test medium may increase sensitivity, but the cost of testing also increases due to helium consumption.
In some applications, by increasing the temperature of the water immersed in it during the test, the pressure of the gas in the tested product is increased and the test performance is improved.

Sızdırmazlık Testi Hava Testi Suya Batırma
Photo: Bubble Leak Test by Water Immersion Method

2. Pressure Decay Test (Pressure Decay Test)

Pressure drop tests are performed using gases such as air or helium. It is one of the most commonly used leakage tests in the industry. Basically, the product to be tested is filled with pressurized gas and by measuring the pressure drop, it is determined whether there is a leak or if there is a leak, what level it is.

It is used quite frequently for the following applications:

  • Welding leak testing
  • Solder leak testing
  • Assembly leak testing
  • Refrigerant leak testing

Two types are widely used in pressure drop tests. While the absolute pressure drop is examined in the first, the relative pressure drop is measured in the second.

a) Absolute Pressure Drop Test (Pressure Decay Test)

During this test, there is a pressure sensor in the system to measure the system pressure. This sensor measures the amount of leakage in the test phase after the system is pressurized. The result is compared with the limit value and whether the part passed the test or not is automatically determined.

The leakage amount is calculated using the following formula:

  Q = ( ∆P x V) / ∆t

Here “Q” indicates the leakage amount, “∆p” indicates the pressure difference between the beginning and the end of the test, “∆t” indicates the test duration. Depending on the capability and properties of the leakage tester, even Pascal levels can be achieved.

As can be understood from the formula, temperature changes can greatly affect the test results. Especially during pressure increase, i.e., filling, the temperature of the fluid increases. On the other hand, during the test phase, there is a decrease in the temperature due to the heat conduction followed by the pressure decrease. The temperature should be kept as constant as possible in order to achieve the desired level of leakage test repeatability.

Another way to increase the sensitivity of the test is to increase the stabilization and test times. In this case, since temperature and pressure fluctuations will decrease, the test result is obtained in a healthier way. However, if testing time increases too much, unit piece testing time may increase, affecting production capacity. The amount of pressure can be increased to shorten the time, but in this case, operator safety becomes an important factor. While generally no special safety measures are required for test pressures of 2 MPa and below, extra safety measures are required at pressures above this.

b) Relative Pressure Decay Test (Pressure Differential Test)

Almost all the points mentioned for the absolute pressure drop test are also valid for this leak test method but it is more sensitive in terms of test results. The difference of the relative pressure drop test is that by adding an non-leaking reference volume to the system as well as the test volume, measurement is taken from both regions and the difference between them is measured to determine whether there is a leak.

There are basically two reasons for precise measurements. These are;

  • Pressure Measurement Sensor Working Range: In absolute pressure test, one sensor measures the test pressure for a wide range. (for example, 0-6 bar), the test pressure sensor must be a product that takes precise measurement at the test pressure level. However, sensors operating in such a wide range and at these levels cannot be very sensitive to detect small pressure changes. There are two sensors in the relative pressure test. One of the sensors measures the test pressure, that is, the large pressure value, and the other sensor measures the pressure difference between the reference volume and the test volume. Thus, very small pressure differences can be obtained much more precisely, thus increasing test sensitivity.
  • Elimination of Temperature Change Effect: Temperature fluctuations are similar in the relative pressure test in 2 test volumes. Since the leakage value is determined by taking the difference between these two volumes, the effect of temperature fluctuations is minimized.
Selecting of Reference Test Volume in Relative Pressure Decay Test

While selecting the reference volume for the relative pressure drop tightness test, it is possible to proceed as follows:

  • If the volume to be tested is small (like a few cm ^ 3), the internal volume of the device measuring the leakage can be considered as the reference volume.
  • A leak-proof volume close to the volume of the test piece can also be used as a reference volume.
  • The most effective way is to use a precisely sealed test piece sample to be used as a master piece. This reference volume, which consists of the same material and internal structure as the test piece, will behave very similarly in temperature and pressure waves, so a very sensitive measurement result will be obtained.

3. Vacuum Leak Test

The vacuum leakage test works with the opposite logic of the pressure drop test. The air in the inner volume of the part to be tested is taken by the vacuum pump and the vacuum is stabilized. If there is a leak on the part, this is detected by an increase in internal pressure.

In the tests conducted with this method, temperature changes do not affect the results since there is almost no air in the environment. In addition, since the amount of leakage is measured for low pressure levels, the sensors used in the tests can be selected very precisely.

As a disadvantage, theoretically, it can be applied for leakage tests occurring in pressure range of 1 bar and below, since maximum 1 bar pressure difference can be created. In addition, it is not possible to apply on parts that are likely to be crushed under vacuum. Of course, they do not provide information about the location of the leak, similar to other pressure differential measurement tests.

Video: Leak Test Devices for Pressure Decay Test Method
Differential Pressure Decay Testing Scheme
Schematics: Pressure Decay Test Flow Diagram
Differential Pressure Decay Test
Graph: Relative Pressure Decay Test – Test Result Graph
Sızdırmazlık Testi Dedektor Kontrollu
Schematics: Sniffer Test Method with detection of leak test location
Vakum Altında Dedektörlü Sızdırmazlık Testi
Schematics: Sniffer Test Method by vacuuming a controlled volume.

4. Tracer Gas Leak Testing

Especially for the tests carried out in large sizes and low pressures, it is the tests carried out by filling various gases to the area where the product to be tested is located and monitoring whether it passes through certain locations. Leak and leak locations can be determined with this method.

Often, Halogen gases, Helium and Hydrogen-Nitrogen mixture are the most frequently used gases in gas monitoring tests.

Halogen gases are the easiest to detect by test devices and equipment, but they pose risks to the environment and human health during use. The test setup should be established considering human health.

Helium gas is getting more and more popular in the industry every day. It is not toxic and flammable, has a very low molecular weight and viscosity, allowing it to be used in a wide range.

Helium gas can easily pass-through gaps and cracks. Under the same environmental conditions, it moves several times faster than air. It is also very easy to detect since its concentration in air is very low (5 ppm). The disadvantage point is; because it travels very slowly in the air, it remains in the test location for a long time therefore there must be some time before testing the next part. In addition, helium sensitive detection equipment and helium test rigs are quite expensive.

Recently, the most used gas type in the leakage test group through gas monitoring; It is 95% nitrogen and 5% hydrogen mixed gas. Here, the gas that makes the real difference and does the job is hydrogen. It is fast and easy to detect at the leak point due to its low molecular weight, low viscosity and high molecular speed. Although it does not harm the environment, its concentration in air is even lower than Helium. Detectors of this mixture are relatively cost effective and the hydrogen nitrogen mixture is readily sold industrially.

Leak testing applications through gas monitoring are carried out using a detector specific to the test gas. They can be made as operator or automatic detector positioning. The special test gas can be divided into two categories as a gas leak test from inside to outside (test volume -> environment) or from outside to inside (environment-> test volume).

a) Sniffer Test

In this test method, pressurized gas is filled into the part to be leak tested. Afterwards, leak control and leak detection is made by moving the gas over the possible leakage zones using detectors that detect the gas.

In this system, which has very low initial investment cost, tests with very low sensitivity can be performed. However, the operational cost may be high depending on the gas price to be used.

The most important of the disadvantages of the system is the dependence on the operator and it is essential that the operator navigates the detector at every possible leak point. In addition, the devices are sensitive to even very small quantities of gas, so unnecessary leaks can cause the part to be rejected.

b) Accumulation Leak Testing

Leak test by deposition can be thought of as a more standardized version of the application with the detector by the operator.

The piece to be tested is placed in a sealed chamber so that it is not in contact with the environment. The test volume is then filled with pressurized gas. In case of leakage during the test, the leaked gas is accumulated between the closed chamber and the test piece. The detectors are positioned to quickly detect the test gas leaking into this closed chamber, and with this method, an automatic system independent of the operator is established.

Since this system is built on the accumulation of leaking gas, the locations of the leak points cannot be determined easily. One of the disadvantages is that in large-sized parts, operations such as taking the part into the sealed chamber and sealing the sealed chamber makes it difficult to apply. In addition, the larger the volumes, the longer the test times.

c) Leakage Test with Detector and Vacuum Chamber

Leak test with vacuum chamber is a kind of leak test that is quite complex but gives precise measurement results. In the leak test from inside to outside, the test piece is placed in a closed chamber that will be kept under vacuum in the system. Both between chamber and the part and the inner volume of the part are evacuated by creating a vacuum. Afterwards, the inside of the test piece is filled with the relevant gas. The part under vacuum between the outer chamber and the part is connected to the gas detectors. In this way, any leakage that occurs from the internal volume of the part to the area under vacuum can be detected by the detectors connected to the vacuum line.

In the leakage test system from outside to inside, the above-mentioned system is operated in the opposite way and the test is carried out.

The advantages of this system are that it is not operator dependent and it is the method by which the most precise measurements can be taken.

As a disadvantage, the system is quite high in terms of both initial investment and operational cost. In addition, it is not possible to determine the test location as a result of the test.

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