1、 Test purpose

The main purpose of integrity testing is to verify the physical integrity and filtering performance of the bag filter, ensuring that it can effectively intercept harmful substances such as impurities, bacteria, and viruses during operation, thereby protecting the safety of downstream equipment and products.

2、 Testing method

There are various methods for integrity testing of bag filters, but overall they can be divided into two categories: destructive testing and non-destructive testing.

1. Destructive testing

For sterilization grade capsule filters, destructive testing usually refers to bacterial challenge testing. This testing method evaluates the sterilization ability of the filter by injecting a high concentration of bacterial solution into the filter and then detecting whether bacteria pass downstream of the filter. However, since this testing method can damage the filter, it is generally only used in specific situations.

2. Non destructive testing

Non destructive testing methods are more favored because they do not cause damage to the filter, mainly including the following:

Bubble point test: Bubble point test is based on capillary principle, which detects the maximum pore size in the filter membrane by gradually increasing the gas pressure. When the gas pressure reaches a certain value, the liquid in the filter membrane begins to be squeezed out and bubbles are generated, and the pressure at this point is the bubble point value. The bubble point value is directly related to the pore size of the filter membrane, and can therefore be used to evaluate the integrity of the filter. The bubble point test is suitable for small bag filters, such as filter membranes installed in membrane fixtures, filter cartridges in filter housings, etc.

Water Intrusion Test (WIT): WIT is an online integrity testing method for hydrophobic membrane filters. This test evaluates the integrity of the filter by measuring the rate of decrease in air pressure upstream of the filter at a specific pressure. Due to the surface tension and capillary phenomenon of water on hydrophobic filter membranes, the integrity of the filter can be determined by observing whether water truly passes through the membrane. The WIT testing method uses water as the medium, avoiding the use of organic solvents during the testing process, and the testing process is highly sensitive.

Diffusion flow testing: Diffusion flow testing is based on the dissolution diffusion model, which evaluates the integrity of the filter by measuring the diffusion airflow passing through the wetted filter membrane at a constant pressure. Due to the pressure difference on both sides of the membrane, gas molecules will dissolve into the wetting liquid from the high-pressure side and diffuse to the low-pressure side. By detecting the integrity of the diffusion flow, the performance of the filter can be indirectly reflected. The diffusion flow test is suitable for large-area filters because the diffusion flow is larger during the testing process, which can more accurately reflect the performance of the filter.

3、 Test steps

Taking bubble point testing as an example, the basic steps of integrity testing for bag filters include:

Preparation stage: Connect the capsule filter to the integrity detector and completely wet the filter membrane pores with a wetting solution (such as water, buffer solution, or filter media solution). For hydrophobic membrane filters, it may be necessary to use a liquid with lower surface tension (such as a mixed solution of alcohol and water) for wetting.

Testing phase: Start the integrity tester and gradually increase the gas pressure. During the testing process, observe and record the generation of bubbles or changes in gas flow rate on the filter membrane. When the gas pressure reaches the bubble point value, record this value and compare it with the integrity verification value of the filter.

Result analysis: Determine whether the filter has passed the integrity test based on the test results. If the bubble point value is within the allowable range and no significant gas leakage or abnormal increase in flow rate is observed, it can be considered that the integrity of the filter is good.

In summary, integrity testing of bag filters is an important measure to ensure stable performance and safe operation of filters. By selecting appropriate testing methods and strictly following testing steps, potential issues in the filter can be identified and addressed in a timely manner, thereby ensuring the safety of downstream equipment and products.