Plate heat exchanger has been widely used in the fields of food, machinery, metallurgy, petrochemical industry and shipping. It has the characteristics of high heat transfer coefficient, small pressure drop, compact structure, light weight, small occupied space, convenient combination of area and process, and strong universality of parts. It has become the preferred equipment for rural central heating projects. In order to ensure the normal operation of the heat exchanger, we need to master the common faults and solutions of the heat exchanger.

 Common faults of plate heat exchanger
1. external leakage
It mainly means that the leakage is small, and the water drop is discontinuous and the leakage is large. The main parts of the continuous water drop leakage are the sealing between the plates, the leakage groove of the second seal of the plates, and the inner side of the end plates and the compression plates.

2. liquid leakage
The main feature is that the medium on the higher pressure side is cascaded into the medium on the lower pressure side, and the system will show abnormal pressure and temperature. If the medium is corrosive, it may also cause corrosion of other equipment in the pipeline. Liquid leakage usually occurs in the diversion area or the secondary sealing area.

3. high pressure drop
The pressure drop at the inlet and outlet of the medium exceeds the design requirements, even many times higher than the design value, which seriously affects the requirements of the system for flow and temperature. In the heating system, if the pressure drop at the hot side is too large, the primary side flow will be seriously insufficient, that is, the heat source is insufficient, resulting in the secondary side outlet temperature can not meet the requirements.

4. heating temperature cannot meet requirements
The main feature is that the inlet temperature is too low to meet the design requirements.

Cause analysis and treatment method
1. causes of external leakage:
The clamping size is not in place, the sizes are uneven, and the size deviation shall not be greater than 3mm, or the clamping bolt is loose.
Local sealing gasket is separated from the sealing groove, there is dirt on the main sealing surface of the sealing gasket, the sealing gasket is damaged or the gasket is aging.
The plate is deformed, and the assembly is misaligned, resulting in pad running.
There are cracks in the sealing groove of the plate or in the secondary sealing area. Example: many heating stations in Beijing, Qinghai, Xinjiang and other places use saturated steam as the primary side heat source for heating. Due to the high steam temperature and the instability of the system at the initial stage of equipment operation, the rubber gasket fails at high temperature, causing steam leakage.

2. disposal method for external leakage
In the non pressure state, the equipment shall be re clamped according to the clamping size provided by the manufacturer. The size shall be uniform. The deviation of the pressing size shall not be greater than ± 0.2nmmn, which is the total number of plates. The parallelism between the two pressing plates shall be kept within 2mm.
Mark the leaking parts, disassemble the heat exchanger, check and solve them one by one, and reassemble or replace the gaskets and plates.
Disassemble the heat exchanger, repair the deformed parts of the plate or replace the plate. If there is no spare plate, the deformed plate can be temporarily removed and reassembled for use.
When reassembling the disassembled plates, clean the plate surface to prevent dirt from adhering to the gasket sealing surface.

3. causes of liquid leakage
-Due to improper selection of plates, cracks or cracks may occur in the corrosion of plates.
-The operating conditions do not meet the design requirements.
-Stress corrosion is caused by residual stress after cold stamping and too small clamping size in assembly.
-There is slight leakage at the plate leakage groove, causing harmful substances in the medium, such as C1 concentration, to corrode the plate, forming a liquid string. Example: a 254smobr03 plate heat exchanger in the sulfuric acid system of an Aluminum Co., Ltd. showed corrosion leakage of carbon steel pipe at the cooling water side and acid leakage to the cooling water side after 5 months of operation. Serious corrosion and cracking were found at the acid inlet and diversion area of the plate. The field analysis shows that the process parameters such as the operating temperature, flow rate and concentration of the system are beyond the design conditions, and the operating temperature is far beyond the applicable range of the material. The plate heat exchanger using saturated steam as the primary side heat source is prone to plate corrosion during operation, resulting in product liquid leakage. This is because the steam temperature is high, and it is easy to cause the rubber gasket to fail under high temperature during equipment operation, resulting in steam leakage and rapid condensation in the secondary sealing area. With the external leakage from time to time, more and more condensate residues are accumulated, and a region with High Cl mass concentration is formed locally, which reaches the corrosion condition of damaging the passivation layer on the surface of the plate. At the same time, due to the large internal stress formed by cold stamping of plates in this area, the internal stress will lead to stress corrosion when the external passivation layer is damaged.

Disposal method of liquid leakage
-Replace the cracked or perforated l plate, and use the light transmission method to find the plate cracks on site.
-Adjust the operating parameters to meet the design conditions.
-The clamping dimension of the heat exchanger during maintenance and assembly shall meet the requirements, and the smaller is not the better.
-Plate data shall be matched reasonably.