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Common faults and troubleshooting of plate heat exchangers: Plate heat exchangers feature high heat transfer coefficients, low pressure drops, compact structures, light weight, small space requirements, easy combination of area and flow configurations, high degree of part interoperability, a wide range of available materials, and ease of large-scale production. They are widely used in industries such as food processing, machinery, metallurgy, petrochemicals, and shipbuilding, and have become the primary heat exchange equipment in urban central heating systems. To ensure the proper operation of plate heat exchangers and extend the service life of their key components (such as plates and gaskets), it is particularly important to understand the faults that occur in these exchangers, their causes, and the methods for addressing them. 1 Common faults of plate heat exchangers 1 External leakage is mainly manifested as seepage (a small amount, intermittent drops of water) and leakage (a larger amount, continuous drops of water). The main locations where external leakage occurs are the seals between the plates, the secondary sealing leakage grooves of the plates, and the areas where the end plates meet the inner side of the compression plate. 1. Fluid crossover: The main characteristic is that the fluid on the side with higher pressure seeps into the fluid on the side with lower pressure, resulting in abnormal pressure and temperature levels in the system. If the medium is corrosive, it may also cause corrosion of other equipment in the pipeline. Leakage usually occurs in the flow guiding area or the secondary sealing area. 1. High pressure drop: The pressure drop at the inlet and outlet of the medium exceeds the design requirements, sometimes even by many times, which severely affects the system’s ability to meet the requirements regarding flow rate and temperature. In a heating system, if the pressure drop on the hot side is too high, the flow rate on the primary side will be severely insufficient; in other words, there won’t be enough heat source, which results in the outlet temperature on the secondary side not meeting the required standards. 1.4 The heating temperature does not meet the requirements; the main characteristic is that the outlet temperature is too low and fails to reach the design specifications. 2 Cause analysis and treatment methods 2.1 External leakage 2.1.1 Causes ① Inadequate clamping dimensions, uneven dimensions in various areas (the deviation in dimensions should not exceed 3 mm), or loose clamping bolts. ② Some gaskets have come loose from their sealing grooves; the main sealing surface of the gaskets is contaminated; the gaskets are damaged or the gasket material has aged. ③ Deformation of the plates and misalignment during assembly cause the running mat to shift. ④There are cracks at the plate seal groove or in the secondary sealing area. Example: Multiple heat stations in places such as Beijing, Qinghai, and Xinjiang use saturated steam as the heat source on the primary side for heating. Due to the high temperature of the steam, when the system is not stable during its initial operation, the rubber gaskets fail under these high temperatures, resulting in steam leakage. 2.1.2 Treatment method ① Under pressure-free conditions, re-clamp the equipment using the clamping dimensions provided by the manufacturer; these dimensions must be consistent, and the deviation in the clamping force should not exceed ±0.2 N/mm (N). For the total number of plates, the parallelism between the two compression plates should be maintained within 2 mm. ② Mark the areas where there is leakage, then disassemble the heat exchanger to identify and address the issues one by one, reassembling or replacing the gaskets and plates. ③ Disassemble the heat exchanger, repair the deformed plates or replace them. When plate spare parts are unavailable, the deformed plate can be temporarily removed and reassembled for use. ④When reassembling the separated plates, the plate surfaces should be cleaned to prevent dirt from adhering to the sealing surfaces of the gaskets. 2. Leakage 2. Causes ① Corrosion of the plates due to improper selection of materials, resulting in cracks or holes. ②The operating conditions do not meet the design requirements. ③ Residual stresses resulting from the cold stamping of the sheet metal, combined with overly tight clamping dimensions during assembly, cause stress corrosion. ④There is a slight leakage at the plate leakage groove, which causes harmful substances in the medium (such as C1) to concentrate and corrode the plates, resulting in cross-connection of fluids. Example: In the sulfuric acid system of a certain aluminum manufacturing company, a BR03 plate heat exchanger with 254 SMo plate material developed corrosion and leakage in the carbon steel connections on the cooling water side after 5 months of operation, resulting in acid leaking into the cooling water side. Inspections revealed severe corrosion and cracking at the acid inlet of the plate as well as in the flow guidance area. On-site analysis showed that process parameters such as operating temperature, flow rate, and concentration exceeded the design specifications, with the operating temperature being well above the range suitable for the material. Plate heat exchangers that use saturated steam as the primary heat source are prone to plate corrosion during operation, which leads to product cross-contamination. This is due to the high temperature of the steam; during operation, the rubber gaskets can easily fail under such high temperatures, resulting in steam leakage and rapid condensation in the secondary sealing area. As the leakage continues, more and more condensation residue accumulates, creating areas with a high concentration of Cl, which meet the corrosion conditions necessary to destroy the passivation layer on the surface of the plates. At the same time, due to the high internal stresses generated by cold stamping of the plates in this area, stress corrosion occurs as a result of the action of these internal stresses when the surface passivation layer is damaged. Treatment method ① Replace the cracked or perforated plates; use the light-transmission method on-site to locate cracks in the plates. ②Adjust the operating parameters to meet the design conditions. ③When repairing and assembling heat exchangers, the clamping size must meet the required standards; it’s not the case that the smaller it is, the better. ④ The sheet materials are properly matched. 2.3 Excessive pressure drop 2.3.1 Causes ① The piping of the operating system was not properly purged; in particular, many contaminants such as welding slag entered the interior of the plate heat exchanger. Due to the narrow flow area within the plate heat exchanger, deposits and suspended particles accumulate in the corners and guide areas, resulting in a significant reduction in the flow area there and causing the majority of the pressure loss to occur at these locations. ② When selecting a plate heat exchanger for the first time, if its area is too small, the flow velocity between the plates becomes too high, resulting in a large pressure drop. ③ After operating for a period of time, plate heat exchangers experience excessive pressure drop due to scaling on the surface of the plates. 2.3.2 Treatment methods: ① Remove dirt or scale from the flow channels of the heat exchanger; for newly operational systems, cleaning should be carried out once a week depending on actual conditions. Clean the scale on the surface of the plates (mainly referring to CaCO3). ) At that time, a cleaning solution containing 0.3% aminosulfonic acid or an 0.8% nitric acid solution containing 0.3% urotropine, 0.2% aniline, and 0.1% potassium thiocyanate is used, with a cleaning temperature of 40–60°C. When performing chemical immersion cleaning without removing the equipment, it is necessary to open the inlet and outlet ports for the cold medium in the heat exchanger; or, when installing the equipment, DN25 cleaning ports should be installed on the medium inlet and outlet pipes. The prepared cleaning solution is then poured into the equipment, and after immersion, the remaining acidic liquid is washed away with clean water to ensure that the pH level is ≥7. When disassembling for cleaning, soak the plates in the cleaning solution for 30 minutes, then gently brush off the scale with a soft brush, and finally rinse thoroughly with clean water. During the cleaning process, care should be taken to avoid damaging the plates and rubber gaskets. If the mechanical backwashing method without disassembly is used, a connection should be installed in advance on the inlet and outlet pipes of the medium, in order to link the equipment to a mechanical cleaning vehicle. The cleaning solution is then injected into the equipment in the opposite direction to the flow of the medium; the cleaning cycle lasts 10–15 minutes, with the flow rate of the medium controlled at 0.05–0.15 m/s. Finally, rinse several times with clean water to keep the mass concentration of Cl in the water below 25 mg/L. ② For secondary circulating water, it is preferable to use softened water; generally, the mass concentration of suspended solids in the water should not exceed 5 mg/L, the diameter of impurities should not be greater than 3 mm, and the pH value should be ≥ 7. When the water temperature is not greater than 95°C, the Ca and Mg concentrations should not exceed 2 mmol/L ； When the water temperature is greater than 95°C, the concentrations of Ca and Mg should not exceed 0.3 mmol/L, and the mass concentration of dissolved oxygen should not exceed 0.1 mg/L. ③For centralized heating systems, the method of replenishing water to the secondary side once can be used. 2. The heating temperature does not meet the requirements. 2. Causes: ① Insufficient flow rate of the fluid on the primary side, resulting in a large temperature difference on the hot side and a low pressure drop. ② The temperature on the cold side is low, as are the temperatures at the cold and hot ends. ③ The flow distribution among multiple plate heat exchangers operating in parallel is uneven. ④Severe scaling inside the heat exchanger. Solution ① Increase the flow rate of the heat source or enlarge the diameter of the heat source medium pipeline. ② Balance the flow rates of multiple plate heat exchangers operating in parallel. ③Disassemble the plate heat exchanger to clean the scale on the surface of the plates.