Leakage in tube and tube heat exchangers is a common equipment management problem in the use of heat exchangers. Leakage is mainly caused by corrosion. A small part of the reason is due to defects in heat exchanger selection and heat exchanger manufacturing processes. There are two main types of corrosion in tubular heat exchangers: electrochemical corrosion and chemical corrosion. In the manufacture of tubular heat exchangers, manual arc welding is usually used to weld tube sheets to tube sheets. The shape of the weld has defects such as depressions, pores, and slag inclusions, and the stress distribution of the weld is uneven. During use, the tube sheet part is usually in contact with industrial cooling water. Impurities, salts, gases and microorganisms in the industrial cooling water will cause corrosion to the tube sheet and welds. This is what we often call electrochemical corrosion. The results show that industrial water, whether fresh water or seawater, will produce various ions and dissolved oxygen, among which changes in chloride ions and oxygen concentration play an important role in the corrosion morphology of metals. In addition, the complexity of the metal structure also affects the corrosion morphology. Therefore, pitting corrosion and crevice corrosion are the main corrosion types of welds between tube sheets and tube rows. From the appearance, a large amount of corrosion products and deposits will be produced on the surface of the tube sheet, with pits of different sizes. Galvanic corrosion also occurs when seawater is used as a medium. Chemical corrosion is the corrosion of media.
       The main factors causing tube plate corrosion of tube heat exchangers are as follows:
       (1) Medium composition and concentration: Concentration has different effects on corrosion. For example, in hydrochloric acid, generally the greater the concentration, the more serious the corrosion. Carbon steel and stainless steel corrode seriously in sulfuric acid, and the concentration is50%around, but when the concentration increases60%Above that, corrosion drops sharply.
       (2) Impurities: Harmful impurities include chloride ions, sulfide ions, cyanide ions, ammonia ions, etc., which can cause severe corrosion in some cases.
       (3) Temperature: Corrosion is a chemical reaction. As temperature rises10℃, the corrosion rate increases1~3times, but there are exceptions.
       (4)pHValue: NormalpHThe smaller the value, the more corrosive the metal is;
       (5) Flow rate: In most cases, the greater the flow rate, the greater the corrosion.