Efficient filter leak detection operation

Firstly, let'sEfficient filter leak detection operationExplain its purpose.

In the process of drug production, in order to ensure that the clean area environment continues to meet the requirements, it is necessary to regularly monitor the high-efficiency filters.According to EU GMP requirements, high-efficiency filters must be scanned and leak checked at least annually. A. Grade The integrity testing of high-efficiency filters in Zone B is conducted every six months, while for other clean level high-efficiency areas, it is conducted once a year.

According to the national standard GB/T 13554-2020 for high-efficiency air filters, there are control requirements for leak detection of high-efficiency filters.

Detail diagram of leak detection operation for high-efficiency filter

Efficient filter leak detection operationThe process is mainly divided into two parts:

1、 Preparation work

Confirm the air volume before starting the inspection, and operate the air conditioner between 80% and 120% of the designed air volumeSelf purification for 30 minutes. The laser dust particle counter is within its calibration validity period and the pressure difference in the clean area meets the requirements. The detection status is static, and there should not be more than two indoor detection personnel. Remove the diffuser plate of the high-efficiency filter and clean the outer surface of the box or frame to avoid dust accumulation that may interfere with the detection. Turn off the fire alarm system in the clean city area to avoid misunderstandings caused by smoke leakage. Prepare a testing plan and corresponding testing records.

2、 Sampling

1. When the aerosol generator upstream of the receiving filter is not turned on, check whether the laser dust particle counter used is self cleaning and reset;

2. Connect one end of the sampling tube to the sampling port of the laser dust particle counter and the other end to the sampling port. Click the sampling button;

3. Manually drive the scanning probe to a distance of about 2-3 centimeters from the surface of the filter, and conduct inspections along the entire cross-section, head glue, and inner frame of the back alkali filter. The scanning speed should be less than 5 centimeters per second, and the scanning should be performed back and forth in a straight line, with an overlap of about 1 centimeter between each line.

Manually drive the scanning probe to a distance of about 2-3 centimeters from the surface of the filter, and conduct inspections along the entire cross-section of the back alkali filter, the head adhesive, and the inner frame of the filter. The scanning speed should be less than 5 centimeters per second, and the scanning should be performed back and forth in a straight line, with an overlap of about 1 centimeter between each line.

The sampling process continues until all scans are completed. After completion, repeat the above process and test again. After completing two measurements, determine whether the high-efficiency filter has leaked based on the test results.

It should be noted that excessive force should be avoided during operation to avoid damaging the high-efficiency filter; During the testing process, personal safety should be taken into consideration and the testing instrument should not be placed too far or too close to the high-efficiency filter.

Efficient filter leak detection operationActual problems encountered during the process:

High efficiency filters are generally carried out after adjusting and balancing the system air volume and the air volume of each air outlet. According to the specifications, the deviation between the air volume of each air outlet and the designed air volume is less than 15%, which meets the conditions for the tested air outlet to operate at a speed close to the design wind speed. So when the air volume is balanced, it is necessary to promptly detect the leakage of the high-efficiency filter.

In engineering, the minimum particle size channel of the particle counter generally used for purification systems larger than level 100 is 0.3 μ m. Therefore, the controlled particle size of the high-efficiency filter being tested on the upwind side is ≥ 0.5 μ m, and its concentration must be ≥ 3.5 × 104pc/L, while the concentration of general atmospheric dust is 5.3 × 104-2.5 × 105pc/L, which is within the upper limit range of the particle counter reading.

In many purification systems, the fresh air entering the circulating air conditioning unit is processed by a filter, and its concentration is much lower than that of atmospheric dust. When mixed with the return air, the concentration will be even lower. Therefore, introducing the atmosphere into the installed purification air conditioning system is a matter worthy of careful consideration. In order to ensure the required particle concentration upstream of the tested air filter without disrupting the balance of the system airflow, introducing uniformly concentrated artificial aerosols upstream is an ideal means. The required aerosol concentration actually depends on the efficiency of the installed high-efficiency filter and the resolution of the particle counter. The minimum bit of a particle counter is units, and the minimum bit is zero. Testing instruments generally have dead zones. If the required downstream concentration is less than 10, it is considered qualified. It is difficult to guarantee the validity of these data according to statistical principles.

Nowadays, in China, the classification of high-efficiency filters is mostly based on the filtration efficiency of 0.3 μ m particles in the American DOP test. Therefore, when using the counting scanning method for leak detection, the measured particle size should be ≥ 0.3 μ m, which has better requirements for upstream concentration. If the efficiency of the high-efficiency filter is 99.97% and the downstream concentration is kept within three significant figures, it is required that the concentration of particles with a diameter ≥ 0.3 μ m in the upstream air be at least about 6 × 104pc/L. If a high-efficiency filter with 99.99% efficiency is used, the concentration of upstream particles ≥ 0.3 μ m is about 2 × 105pc/L. At this point, the concentration of upstream particles ≥ 0.5 μ m is much higher than 3.5 × 104pc/L. So, using the atmosphere as a dust source can no longer meet the testing requirements.

High flow particle counters are more suitable for detecting installation leaks of high-efficiency filters. The larger the air sampling volume, the more representative the test results are, and the higher the accuracy. The sampling volume required by the specifications is 1l/min, while we often use a sampling volume of 0.1cfm (2.83l/min) to meet the requirements of the testing instrument, but this will affect the efficiency of leak detection work. Taking the 610 × 610 high-efficiency filter as an example, when using a mobile sampling head to sample under the high-efficiency filter, the sampling speed is 20mm/s, and the rectangular 100 × 11.33 sampler takes at least 244 seconds; The sampling speed of the circular sampler is slower, and the time required for leak detection scanning is longer. The calculation rules for scanning rate and acceptable observation count in ISO14644-3 "Metrology and Test Methods" are difficult for general engineering and technical personnel to master. Therefore, in the future, when formulating regulations in this area, it is recommended that appropriate sampling rates and acceptable observation counts be used for different levels of high-efficiency filters to facilitate practical operation by engineering testing personnel.