A heat exchanger is a device that transfers part of the heat of a hot fluid to a cold fluid, also known as a heat exchanger. A heat exchanger is a device that transfers part of the heat of a hot fluid to a cold fluid, also known as a heat exchanger. Heat exchangers are common equipment in the chemical, petroleum, power, food and many other industrial sectors and occupy an important position in production. In chemical production, heat exchangers can be used as heaters, condensers, evaporators and reboilers. Under the action of chemical or electrochemical action of the surrounding medium, and often in combination with physical, mechanical, chemical or biological factors, the destruction (corrosion) of the metal, that is, the metal is not allowed under the action of its environment. Avoid the phenomenon of reacting with the medium.
When the heat exchanger is manufactured, the welding of the tube sheet and the tube is generally performed by manual arc welding. The shape of the weld has different degrees of defects, such as depressions, pores, slag inclusions, etc., and the weld stress distribution is not uniform. When used, the tubesheet portion is generally in contact with industrial cooling water, and impurities, salts, gases, and microorganisms in industrial cooling water can cause corrosion to the tube sheets and welds. Studies have shown that industrial water, whether fresh water or sea water, has various ions and dissolved oxygen. The concentration of chloride ions and oxygen changes, which plays an important role in the corrosion shape of metals.
In addition, the complexity of the metal structure also affects the corrosion pattern. Corrosion concentrated on individual small points on the metal surface is called pitting corrosion, or small hole corrosion and pitting. Severe crevice corrosion occurs in the gaps and covered parts of the metal surface. Therefore, the corrosion of the tube and tube welds is mainly pitting corrosion and crevice corrosion. Viewed from the outside, there are many corrosion products and deposits on the surface of the tube sheet, which are distributed in different sizes. Galvanic corrosion occurs when seawater is used as a medium. "Bimetallic corrosion" is also a common phenomenon of tube sheet corrosion.
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