Use and maintenance of heat exchangers?

After cleaning the 1-system piping, the system is securely connected to the equipment. The heat exchanger inlet should be equipped with a filtration device, and a temporary bypass should be considered. 2. When driving the system, first open the inlet and outlet valves for the heated medium, start the cold-side circulation pump; once everything is operating normally (no leaks or abnormalities), slowly open the hot-side valves, release the steam, and then close them. 3. When the heating medium is introduced during testing, the temperature should be increased gradually to avoid thermal shock or excessive pressure. 4. Once the test temperature is normal, the heat exchanger bolts can be tightened. Maintenance: 1. The pressure under normal operation should be within the maximum operating pressure specified on the equipment’s nameplate; a pressure gauge or pressure protection device should be installed for monitoring. 2. When cleaning the system, the inlet and outlet valves should be closed to prevent the cleaning fluid from entering the heat exchanger. 3. To stop the system from operating, it is necessary to drain the medium inside the heat exchanger to prevent equipment corrosion; in particular, when the system is not in use during winter, the working medium must be completely drained to avoid frost damage. 4. When cleaning the heat exchanger, the chloride ion concentration in the cleaning solution must not exceed 25 ppm. After cleaning, the cleaning solution must be removed completely. Before putting the heat exchanger back into use, it must undergo a pressure test at 1.25 times the nominal pressure; there should be no leaks or abnormalities after 60 minutes.

Key points for the maintenance and repair of heat exchangers: To ensure the long-term proper operation of heat exchangers, it is necessary to carry out maintenance and repairs on these devices in order to guarantee their continuous operation and reduce the occurrence of accidents. During the inspection, in addition to checking the operation records of the heat exchanger, visual inspection is primarily used to determine whether there are any abnormalities. The key points are as follows: 1. Temperature variations – Measure and investigate the changes in the temperatures at the inlet and outlet of each fluid in the heat exchanger, as well as the degree of reduction in heat transfer, in order to assess the extent of contamination. II. Pressure loss situation: It is necessary to determine the extent to which fluid pressure loss increases due to the deposits formed on the inside and outside of the pipes. III. Internal leakage: Internal leakage in heat exchangers includes thinning and perforation caused by tube corrosion and wear ； The expansion section becomes loose due to cracking, corrosion, and vibration ； Wear and perforation caused by contact with the baffle ； Loosening or breaking of the fastening bolts of the floating hood, as well as deterioration of the gaskets in these areas. Due to internal leakage in the heat exchanger, the two fluids mix together; from a safety perspective, it is necessary to immediately disassemble and inspect the device. Under normal circumstances, this can lead to coloring, contamination by impurities, which results in products not meeting specifications and a decline in quality, or even shutdown of the device. Therefore, it is important to detect internal leaks early by taking samples from the low-pressure fluid outlet of the heat exchanger and analyzing them. IV. External Conditions The inspection of the external conditions of a heat exchanger in operation is carried out visually, and the items included are as follows: Inspection of the joint areas: It is necessary to check for any leaks from the welded parts of the main body, flange joints, and pipe connections, as well as to verify whether the bolts are tight. Inspection of the foundation and scaffolding: Check whether the anchor bolts are loose, whether the concrete foundation is cracked or damaged, and whether the steel scaffold legs are abnormally deformed or deteriorated. Inspection of insulation and cooling devices: It is necessary to check for any damage on the exterior of these devices, especially the waterproof layer covering them as well as the supports, as these areas are prone to damage; therefore, careful inspection is required. Coating inspection: Check for any deterioration of the outer coating. Vibration inspection: Check the main unit and connected piping for any abnormal vibrations or unusual noises. In the event of any abnormalities, it is necessary to identify their causes and take the appropriate measures. V. Thickness measurement: For heat exchangers that operate continuously for long periods, there is a concern regarding abnormal corrosion; therefore, the thickness of their shells is measured from the outside as needed, in order to determine the extent of corrosion that has occurred. During measurement, a non-destructive thickness gauge such as an ultrasonic one should be used. VI. Precautions for operation: Heat exchangers should not be subjected to sudden temperature changes. Ordinary heat exchangers are designed with thermal expansion measures taken into account based on their operating temperatures; therefore, sudden temperature changes can generate thermal stress in certain areas, leading to the loosening of the expanded sections or even damage to the tubes. Thus, special care must be taken when the temperature rises or falls. The temperature of the cooling water should not exceed the required level: seawater is used as the cooling water in the heat exchanger. If the temperature at the cooling water outlet exceeds 50°C, it will promote abnormal growth of microorganisms; on the other hand, it will facilitate the decomposition and attachment of by-products, thereby causing rapid corrosion, perforation of the pipes, and a decline in their performance, so this aspect needs to be taken into consideration. Pay close attention to any abnormal increases in pressure and temperature; fully understand the design parameters of the heat exchanger, and use instruments to check for any abnormal rises in pressure and temperature. VII. Disassembly for inspection and maintenance: In accordance with regulations regarding faults and reduced performance of heat exchangers, it is necessary to stop operation periodically and carry out disassembly inspections. The key points are as follows: 1. Visual inspection upon disassembly: To determine the extent of corrosion and deterioration in various components, it is essential to immediately check the level of contamination and the presence of water rust after disassembly, and to conduct sampling and analysis tests as needed. 2. Inspection of the shell, channels, and tube sheet: According to the general structure, inspection of the inner and outer sides after disassembly is carried out—primarily through visual inspection. For the corroded areas, a depth gauge or ultrasonic thickness gauge can be used to measure the wall thickness, in order to determine whether it exceeds the allowable range. Secondly, the channels and partitions often bend due to scale buildup from use and pressure changes, or corrosion occurs as fluid leaks from the front end of the inner partition owing to improper gasket installation. Furthermore, the tube sheet is prone to bending due to stresses during tube expansion, tube blockages, and pressure changes, so tests such as tensile strength testing must be conducted. 3. Inspection of heat transfer tubes: Defects on the inner side of the tubes, within a range of 100 mm from the tube sheet (measured from the tube sheet), can be detected using a micrometer; if they are located beyond this range, an internal tube inspector equipped with a magnifier is required for visual inspection. The size of the defect can be measured using the scales on the inspector, but its depth is difficult to determine accurately by visual inspection. If the pipe material is non-magnetic, an eddy current detector can be used to measure the extent of corrosion. Tube defects in fixed-tube-sheet heat exchangers can also be detected using an ultrasonic flaw detector with the water depth method. 4. Assembly, reset, and testing: After cleaning, inspection, maintenance, or repair, the heat exchanger is assembled and reset in accordance with the specified sequence and procedures; at the same time, a pressure test is conducted to check for any abnormalities. Reasons for the explosion of heat exchangers: 1. Self-made heat exchangers, in which significant changes are made to their structure and materials without proper consideration; as a result, the quality of fabrication is poor, they do not meet the standards for pressure vessels, and the strength of the equipment is reduced. 2. The welding quality of the heat exchanger is poor; in particular, the weld joints are not fully welded, and no weld inspection or pressure testing is carried out. This results in leaks at the weld joints or fatigue fractures, leading to the leakage of large amounts of flammable and explosive fluids and subsequent explosions. 3. Due to corrosion (including stress corrosion and intergranular corrosion), the pressure resistance decreases, leading to the failure of the tube bundle or severe leakage, and explosions may occur when exposed to an open flame. 4. When performing a airtightness test on the heat exchanger, oxygen is used to increase pressure or flammable refining gases are employed for leak detection, which can cause physical and chemical explosions. 5. Violations of operating procedures and operational errors led to the valve being closed, resulting in a pressure overload explosion. 6. The failure to discharge waste over a long period leads to an accumulation of flammable and explosive substances such as nitrogen trichloride; combined with excessively high operating temperatures, this can cause violent explosions in heat exchangers such as those used for liquid chlorine. 7. Peroxide explosion. Reasons for heat exchanger leaks: Most combustion explosions, asphyxiation, poisoning, and burn incidents involving heat exchangers are caused by leaks. If flammable and explosive liquids or gases leak and come into contact with an open flame, it can lead to fires and explosions; the release of toxic gases can cause asphyxiation and poisoning, while the leakage of highly corrosive fluids can result in burns. The areas most prone to leakage are the weld joints, the connections between the head and the tube sheet, the connections between the tube bundle and the tube sheet, and the flange connections.

It has been explained in detail above; I’m providing links to some previous related questions for the original poster’s reference. The link to the posts on heater maintenance is http://bbs.hcbbs.com/search.php?searchid=1516&orderby=lastpost&ascdesc=desc&searchsubmit=yes, and the link to the posts on heater usage is http://bbs.hcbbs.com/search.php?searchid=1514&orderby=lastpost&ascdesc=desc&searchsubmit=yes