First, leak test In order to find out the leakage of the pipeline, we must first do a hydraulic test, and generally adopt an external pressure test that exerts pressure on the outside of the pipeline. The method is as follows: pump water into the shell and keep it for a certain time, visually check the leakage of the pipes at the tubesheets at both ends, and record the leakage of the pipes. Second, the leakage of the pipeline itself is generally irreparable. If the number of leaking pipes is small, the two ends of the nozzle can be blocked with conical metal plugs. For example, when the pressure on the pipe side is high, it is more reliable to weld after plugging. The length of the plug is generally twice the inner diameter of the pipe, the diameter of the small end should be equal to 0.85 times the inner diameter, and the taper should be 1: 10. The hardness of the plug material should be lower than or equal to the hardness of the pipe. When plugging pipes to eliminate leakage, the number of plugging pipes shall not exceed 10%. 1. Corrosion of heat exchange tubes due to dirt, scale in medium and eddy current abrasion of inlet medium, it is easy to cause corrosion of heat exchange tubes, especially at the inlet end of heat exchange tubes of 40~50mm, which is mainly caused by eddy current disturbance by the fluid in the dead corner. 2. There is stress concentration at the joint between the pipe and the tubesheet, the joint between the pipe and the tubesheet, and the joint between the pipe and the baffle, which is easy to produce cracks at the expansion joint. When there is a gap between the tube and the tubesheet, it is easy to cause the accumulation of Cl+ and the enrichment of oxygen, so it is easy to form pits or crevice corrosion on the surface of the heat exchange tube, which will become the crack source of SCC. The fracture of the joint between the pipeline and the baffle is often due to the long pipeline, many baffles and slight bending of the pipeline, which is easy to cause local stress concentration between the pipe wall and the baffle and the existence of cracks, so the joint becomes the weak link of stress corrosion. Thirdly, shell corrosion is easy to occur because of the poor weld quality between shell and accessories. When the shell medium is electrolyte, the shell material is carbon steel and the tube bundle baffle is copper alloy, electrochemical corrosion is easy to occur and the shell is corroded and perforated. The overhaul contents of the shell-and-tube heat exchanger are as follows: 1. Minor repair contents 1) Dismantle the heads or pipe boxes at both ends of the heat exchanger; 2) Cleaning and cleaning foreign bodies on the inner surface of pipes and shells. And check for defects such as corrosion, rust, cracks and sand holes. Two end covers and pipe boxes of the heat exchanger; 3) Carry out pressure test and leakage test on the tube bundle and shell; 4) Check the bolts, heat preservation and corrosion protection; 5) local thickness measurement. Second, the medium repair content 1) contains minor repair content; 2) Cleaning, cleaning and washing the drawn tube bundle, and checking the deformation and bending of the heat exchange tube; 3) Check the corrosion of partition, baffle and tie rod bolts; 4) Check the sealing surface of the heat exchanger, and there should be no scratches, pits and pits on the surface. III. Overhaul contents 1) include medium repair and minor repair; 2) Check the operation of the heat exchanger comprehensively, and check the welding joint between the tubesheet and the pipe.