Welcome to Anhui Sailer Industrial Technology Co., Ltd. official website




Pressure vessel leak detection system device and process method

2019-05-05 16:00 admin
For pressure vessels, the purpose of the helium leak test is to detect if there is a small amount of leakage in the container. It is generally suitable for containers that are extremely hazardous to the medium. The so-called helium leak test is a vacuum method. The vacuum method can be applied to a heat exchanger, but it is difficult to operate for a container, and once a leak is found in a vacuum test, the specific leak position and leak rate cannot be immediately performed. determination.
Helium leak test device

The helium leak test device consists of a mass spectrometer leak detector, a vacuum pumping unit, a vacuum gauge, a pressure gauge, a valve, and other equipment and instruments.
Vacuum pumping unit

The vacuum unit should have sufficient capacity to evacuate the unit to -01099999MPa (gauge pressure). A large vacuum unit is generally used, and the vacuuming rate is 1 m3 /min. The vacuum unit should also be related to the size of the container. It can be equipped with a two-stage vacuum pump. The first stage is a Roots rotary pump, which can be vacuumed to -0109997MPa (gauge pressure), the second stage is a mechanical pump, which can be vacuumed to -01099999MPa ( Gauge) .
Vacuum gauge

Accuracy of 115, measuring range - 011 ~ 0MPa.
Pressure gauge

The accuracy is 115, and the measuring range is 0~0125MPa.
Test device connection

Connect the vacuum unit and accessories as shown in Figure 1. After all the vacuum facilities and accessories are connected to the container to be inspected, the vacuum valve, vacuum hose connection, vacuum gauge, etc. should be tested. It must be strictly inspected without leakage and completely sealed before use.
operating
Pre-test preparation procedure

(1) The airtightness test is performed on the sealed equipment with dry air or dry nitrogen.

(2) The inside of the equipment, the flange sealing surface and the gasket should be cleaned and greased.

(3) All equipment flanges and adapter flanges sealed with gaskets shall be sealed with a clean plastic film at the flange joints.

(4) All welds including longitudinal and circumferential joints, butt joints with flanges, the fillet welds of the joints and casing are covered with clean plastic film (cannot touch the weld), tape is used at both edges Sealed.

Nitrogen replacement Because residual moisture and oil molecules can impede possible leakage, affecting the correctness of the helium leak test, the equipment to be inspected should be vacuumed by means of siphoning to ensure the interior of the equipment is dry and clean.

Sufficient vacuum removes residual moisture and oil molecules. The equipment is required to have a vacuum of at least - 0109 MPa (gauge pressure). When the vacuum degree of the system reaches - 0109 MPa (gauge pressure), nitrogen gas is charged to 0 MPa (gauge pressure) to clean and replace residual moisture. Then re-vacuate to - 0109MPa (gauge pressure). At this point the device is fully dry and can be filled with helium. 213 Fill the equipment with helium gas, pressurize the pressure to 0MPa (gauge pressure), then charge the nitrogen into the equipment to a pressure of 011MPa (gauge pressure). The equipment is kept under pressure and the holding time is not less than 30 minutes.
Detection

(1) Set the molecular mass of the helium mass spectrometer leak detector to 4.

(2) Calibrate the probe with a standard leak block in the helium mass spectrometer and record the output voltage value Us of the standard leak block. The probe should be calibrated every 20 times, and the detection time should not exceed 1 hour.

(3) The probe is inserted into the helium mass spectrometer to detect and record the film area.

(4) Inspection of the tube and tube sheet welds of the heat exchanger.

Each weld must be tested from the weld line to the center of the weld. The distance between the probe and the detected weld should be kept at 1 to 3 mm during the test. The test should start from the weld at the bottom position and then gradually increase. Mark and record each weld detected.

After each tube is tested, wrap each side of the tube sheet with a plastic film and tape the edges. After 1 h, insert the probe to detect and record the film area.
Leak rate Qp calculation

The output value of the mass spectrometer ZLS - 24B is the voltage value, which is converted to the actual leak rate according to the following formula:

Qp = (Up /Us )/Q0

Where Up ——— 氦 mass spectrometer detects the voltage value;

Us ———The voltage value when the probe is calibrated;

Q0 ———The leakage rate of the standard leak block.
assessment

If the leak rate Qp of each of the detected regions does not exceed the allowable leak rate, which is generally 1 × 10 - 6 Pa·m 3 /s, the area to be inspected is acceptable.
in conclusion

The positive pressure method is used for the helium leak test. It is not only easy to operate, but also the test results are straightforward. It is suitable for the helium leak test of a large volume pressure vessel.