Maintenance and repair techniques for plate heat exchangers　

(1) Maintain content

1) Intermediate repair content

① Dismantle import and export pipelines and clean up debris;

② Check the rubber lining of the import and export pipelines to ensure that there are no cracks or damage;

③ Check and measure the pre tightening force of bolts and the external dimensions of the plate.

2) Maintenance content

① Including intermediate repairs.

② If the heat exchanger scales, it should be removed for cleaning or undergo another online chemical cleaning of the pipeline.

③ Check the elasticity and compression deformation of the sealing strip with a magnifying glass, and replace it if necessary.

④ Check the deformation of the heat transfer plate.

⑤ Check the heat transfer plate for defects such as corrosion and perforation.

(2) Maintenance Technology

1) Before disassembling the plate heat exchanger, the external dimensions of the compressed plate heat exchanger should be measured and recorded.

2) Remove the sealing rubber strip. To prevent the threading knife from breaking the sheet, the rubber strip can be quenched and deformed using liquid nitrogen quenching method, and then torn off.

3) Remove any remaining adhesive from the sealing groove.

4) Inspect the heat transfer plate for cracks or perforations using illumination or penetration methods.

5) Clean the dishes with clean water.

6) Reassemble.

7) Airtightness and hydrostatic testing.

(3) Reassemble

1) Before assembly, clean the sealing groove with acetone, apply 401 adhesive, and stick the sealing strip in a horizontal position.

2) Each group consists of 50 sheets with sealing strips, pressed with 20-30mm steel plates to maintain an ambient temperature within the range of 30-35 ℃, and cured for 24 hours.

3) After lifting the components, gently lift the two end covers and secure them with fixing bolts.

4) Use a torque wrench to evenly tighten the bolts.

5) The total compression of the measurement board after assembly can generally be calculated using the following formula:

L=（δ1+δ2）n+δ2

In the formula, l represents the total length of the fastening plate bundle, mm；

δ 1- plate thickness, mm；

δ 2- The thickness of the compressed sealing strip (usually 80% of the uncompressed thickness, 20% compression, and no more than 35% compression), mm；

Number of N-heat transfer plates.

6) Install the inlet and outlet liner. δ

7) Full pressure test. Firstly, plug the inlet pipe of the fluid channel on one side of the plate and fill it with water. Then, add a blind plate with a short exhaust pipe to the outlet pipe of the working fluid channel on the other side of the plate, and install a pressure gauge on the pressure testing side. After filling with water, use a manual pump with 1.25 times the working pressure to pressurize and maintain the pressure for 30 minutes. There is no pressure drop when connecting the outer tube.

8) Unilateral pressure test. To ensure no internal leakage, a single-sided pressure test method can also be used, where one side of the test is filled with water and the other side is not filled with water, and the test pressure is the working pressure. 20 minutes without lowering the pressure is considered qualified. Plate heat exchangers generally do not undergo single-sided pressure testing to prevent significant deformation and damage to the plate heat exchanger and sealing strips.

9) Airtightness test. According to the requirements of plate heat exchangers, a tightness test should also be conducted after the hydrostatic test. The test pressure should be 1.05 times the working pressure. Brush around the plate of the heat exchanger with soapy water and check for any air leaks.