Pressure Decay Leak Testing and How Temperature Affects It
Leak testing is an important quality control method applied in many industries. Although there are different methods, manufacturers prefer leak tests with the pressure decay method. Because the differential pressure decay method is precise, low cost, and simple to apply. Check out our products that work with the principle of the pressure decay method here.
Leak tests with this method are starts with supplying compressed air to the product. BT 4000 Leak Tester monitors the pressure change. Whether there is a leak in the product, BT 4000 Leak Tester decides automatically. BT 4000 uses predetermined parameters such as leak rate and max pressure drop. However, this method is sensitive to changes in environmental conditions.
Ideal Gas Law and Pressure Decay Leak Testing
n= Number of Moles
R= Gas Constant
According to the ideal gas law, the factors affecting the pressure are temperature (T) and the number of moles of gas (n). The temperature change directly affects the pressure change. During the testing of products made of materials with a low expansion coefficient, a temperature change will not cause a volume change. Because of that, the temperature change will cause a proportional increase or decrease in pressure for products made of materials with a low expansion coefficient.
An increase in temperature during the leak test of an exhaust pipe increases the velocity of the gas molecules in the part, which is, the pressure. Even if there is a leak in the product, it may cause the pressure variation to remain within the tolerance. In this way, the leaking product can be mistakenly approved. Likewise, a decrease in temperature may cause the defect-free product to appear leaking.
In products such as rubber with a high expansion coefficient, the temperature change will cause both the volume and the pressure to change. Contact us for more information about these systems tested with the reference product.
Factors That Cause Temperature Change During Leak Testing
Factors that may cause temperature variation when performing leak test with pressure decay method are:
The temperature of the environment
The temperature of the area where the product is tested is an important factor. Consequently, waste heat generated in the factory or infrared heaters located close to the test area can cause temperature changes and reduce the test quality.
The temperature of the part
In some facilities, the products transported for leak tests may be kept at outdoor temperature. When products are brought into the factory environment for testing, their temperature begins to change. Even if the products are leaking, their pressure may increase due to an increase in temperature. Storage conditions of the products in a factory change according to seasonal factors. Products called leaking during pressure decay leak tests may change according to the seasons. In test conditions where the temperature is not constant, it is necessary to test with the reference test method.
Material and purpose of use of the part
Products aimed to transmit heat, such as heat exchangers, are inclined to temperature changes. Likewise, products with high heat transmission coefficients are also vulnerable to temperature changes. The referenced test method can be used in leak tests of these products.
Ambient Air Flow
Airflow causes forced heat convection. Therefore, fans should not be placed in front of the product during leak testing.
Changes in the product temperature during the test phase may cause erroneous results. Controlling test conditions increases the performance of the leak test, allowing a shorter test time.
Keeping temperature and external factors controlled ensures that the correct test results are achieved.