(1) Pitting
Problem manifestation: Small holes appear locally on the surface of the plate. These holes are usually deep and distributed in a dotted pattern. The appearance of pitting will gradually weaken the strength of the plate and may cause leakage of the medium. This is more common when stainless steel plates are used to treat media containing chloride ions. Cause analysis: This is mainly due to the presence of corrosive ions (such as chloride ions) in the medium. When the passivation film on the surface of the plate is destroyed, these ions will form micro-batteries in local areas, accelerating the corrosion of the metal. In addition, the unevenness of the plate surface, such as local scratches and impurity adhesion, can also easily cause pitting. Solution: First, for highly corrosive media such as chloride ions, consider replacing them with more corrosion-resistant plate materials, such as titanium alloys. If stainless steel plates continue to be used, the chloride ion concentration in the medium must be strictly controlled and corrosion inhibitors must be added. At the same time, during installation and maintenance, ensure that the surface of the plate is clean and smooth to avoid scratches. For plates that have already experienced pitting, if the degree of corrosion is light, they can be polished and repaired, and after removing the corrosion products, passivation treatment can be performed; if the corrosion is severe, the plates need to be replaced in time.
(2) Manifestations of crevice corrosion problems: They often occur at the edges where the sealing gasket of the plate contacts the plate, or at the connection between the plates. It manifests as corrosion of the metal in the crevice, which will cause damage to the sealing gasket and leakage of the medium. Cause analysis: Due to the poor flow of the medium in the crevice, a special corrosive environment is formed. In this environment, factors such as the difference in oxygen concentration and changes in the composition of the medium will cause local electrochemical corrosion. For example, when the sealing gasket ages and shrinks, causing the gap to increase, this problem is more likely to occur. Solution: Choose a suitable sealing gasket material to ensure its compatibility with the plate and good sealing performance. During installation, ensure that the gasket is installed in place to avoid excessive gaps. Regularly check and replace aging sealing gaskets. For areas where crevice corrosion has occurred, sealants can be used for local repairs, but if the corrosion is severe, the plate or the entire heat exchanger unit may need to be replaced.
(3) Scale
Problem manifestation: In a plate heat exchanger that processes water media, a layer of white or grayish white hard scale will gradually form on the surface of the plate. The presence of scale will reduce the heat transfer efficiency of the plate, increase the resistance of the fluid, and cause the performance of the heat exchanger to decline. Cause analysis: The solubility of calcium, magnesium and other ions in the water decreases during the heating process, and they precipitate and settle on the surface of the plate. When the water temperature is high and the water hardness is high, the speed of scale formation will accelerate. Solution: For hard water, a softening water device can be installed at the water inlet to reduce the content of calcium and magnesium ions in the water. Clean the plate heat exchanger regularly. Chemical cleaning methods can be used to dissolve scale with acidic cleaning agents, but attention should be paid to controlling the concentration of the cleaning agent and the cleaning time to avoid corrosion to the plate. Physical cleaning methods such as high-pressure water washing or sponge ball cleaning can also be used. (II) Scale
Problem manifestation: A layer of scale formed by impurities such as oil, microorganisms, and silt is attached to the surface of the plate, which makes the heat transfer performance of the plate worse, and may breed bacteria, affecting the quality of the medium. Cause analysis: It is easy to produce when processing media containing oil or impurities. For example, in food processing or chemical production, impurities in the medium enter the heat exchanger without being fully filtered. In addition, when the heat exchanger is running for a long time, microorganisms will multiply in a suitable temperature and medium environment, which will also form dirt. Solution: Install an effective filtering device at the entrance of the heat exchanger to remove large particles of impurities and oil in the medium. For the dirt that has already formed, you can use alkaline cleaning agents to clean it, and for microbial dirt, you can add fungicides to treat it. Backwash and empty the heat exchanger regularly to prevent the accumulation of dirt.
(4) Local deformation
Problem manifestation: Local areas of the plate have bulges or depressions, which will change the shape of the flow channel between the plates, affect the distribution of the fluid and the heat exchange effect, and may also cause collision and wear between the plates.
Cause analysis: It may be due to excessive external force during installation, or excessive local temperature or pressure during operation. For example, when the heat exchanger is partially blocked, the pressure in the area rises sharply, which may cause local deformation of the plate.
Solution: During installation, follow the operating procedures and use appropriate tools to avoid excessive external force on the plate. For local deformation that occurs during operation, if the deformation is small, you can try to use special repair tools for plastic repair; if the deformation is serious, you need to replace the plate. At the same time, check and eliminate the faults that cause local pressure or temperature abnormalities in a timely manner.
(5) Overall deformation
Problem manifestation: The entire plate is bent or twisted, which will seriously affect the normal operation of the plate heat exchanger, resulting in poor sealing and a significant reduction in heat exchange efficiency.
Cause analysis: Usually due to long-term operation under conditions exceeding the design pressure or temperature of the plate, or uneven fixing of the plate during installation, resulting in unbalanced force.
Solution: Strictly control the operating parameters of the heat exchanger to ensure that it is within the design range of the plate. If overall deformation is found, stop operation immediately, check and adjust the installation. For plates that have been severely deformed and cannot be repaired, they must be replaced, and the operating conditions and installation quality of the entire heat exchanger must be fully evaluated and improved.
