Integrity Testing for Beverage Applications
Integrity testing is a fundamental requirement of critical process filtration applications in the beverage industry. By testing the membrane integrity, you guarantee the functionality of your membrane filter assemblies and consequently the quality of your product.
When to perform integrity testing?
In beverage applications, it is recommended to perform filter integrity testing during the final membrane filtration step, before and after use of the filters. Performed before the filters have been used, integrity testing monitors filter integrity prior to batch processing to prevent the use of a non-integral filter. Performed after a batch has been processed, integrity testing can detect if the integrity of the filter has been compromised during the process. The detection of a failed filter alerts of a problem immediately after batch processing and eliminates delay by keeping batches under control.
Which integrity test to perform?
Two classifications of integrity testing are destructive and non-destructive. In beverage applications, the routine test is the non-destructive. There are three types of non-destructive testing: bubble point test, diffusion test and water flow integrity test for hydrophobic filters (the HydroCorrSM Test). The pressure hold, forward flow, and pressure decay tests are variations of the diffusion test.
Due to the size of the filtration area and the type of beverage application, the usual integrity tests are the diffusion test or the pressure hold test. You can not perform the bubble point test in your beverage application, because the high membrane surface area generates significant diffusion rendering the detection of the bubble point very difficult.
Diffusion test
At differential gas pressures below the bubble point, gas molecules migrate through the water-filled pores of a wetted membrane following Fick's Law of Diffusion. The gas diffusion flow rate for a filter is proportional to the differential pressure and the total surface area of the filter. At a pressure approximately 80% of the minimum bubble point, the gas which diffuses through the membrane is measured to determine a filter's integrity.
How to define the diffusion criteria?
Diffusion specifications are provided by the suppliers in the Certificate delivered with the filters. To calculate the total diffusion of a housing containing a number of filters, you use the following formula:
DT = DS X NC
where:
DT is the total diffusion of the housing
DS is the diffusion specification of one filter cartridge (given in the Certificate)
NC is the number of filter cartridges contained in the housing
Your filters and housing are integral if diffusion measured is lower than or equal to DT .
How to proceed?
- Wet the filter with water for hydrophilic membranes or an alcohol/water mixture for hydrophobic membranes.
- Slowly increase pressure on the upstream side of the filter to the recommended test pressure provided by the manufacturer
- Allow the system to equilibrate.
- Measure the gas flow at the outlet for one minute with an inverted graduated cylinder or a flow meter.
- A diffusion flow reading higher than the specification is an indication of one of the following:
- wrong pore size
- temperature other than ambient
- incompletely wetted membrane
- non-integral membrane or seal
- inadequate stabilization time
Pressure Hold Testing
Also known as pressure decay or pressure drop test, pressure hold testing is a variation of the diffusion test. It also depends on the membrane area and has the same sensitivity.
How to define the pressure hold value?
The pressure hold value is dependent on the diffusion flow and upstream volume. It can be calculated using the following equation:
where:
D = Diffusion rate (mL/min)
T = Time (minutes)
Pa = Atmosphere pressure (1 Atm)
Vh = Upstream volume of apparatus (mL)
P = Pressure Drop (bar or psig)
Your filter and housing are integral if pressure hold measured is equal to or lower than ΔP.
How to proceed?
Pressure hold test is performed with the same procedure than the diffusion test, except for step 4: a highly accurate gauge is used to monitor upstream pressure changes due to gas diffusion through the filter.
Pressure hold testing is the method employed by most automated integrity test systems in beverage applications.
| We advise you to test the integrity of you membrane filters with Millipore Integritest Mini II P System that performs a pressure hold test as primary integrity test, but is also able to perform an automatic calculation of the diffusion value based on the fixed upstream volume data you entered in your test recipe. The Integritest Mini II P Systemis a microprocessor-driven portable unit that makes your integrity testing easy. |
Operator Certification Training (Integrity Testing Training and Certification) |
 |
