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      The leakage problem of tube and tube heat exchanger is analyzed

      2017-03-27 focus number:

      Heat exchanger leakage is the most common equipment management problem in the use of heat exchangers. Leakage is mainly caused by corrosion, and part of it is due to the selection of heat exchangers and the manufacturing process defects of heat exchangers themselves. There are basically two forms of corrosion for tubular heat exchangers: electrochemical corrosion and chemical corrosion. In the production of tube and tube heat exchanger, manual arc welding is generally used for the welding between tube and tube, and the weld shape has defects of different degrees, such as depression, porosity, slag inclusion, etc., and the distribution of weld stress is not uniform. When used, the tube plate is generally in contact with the industrial cooling water, and impurities, salts, gases and microorganisms in the industrial cooling water will constitute corrosion to the tube plate and weld. This is often referred to as electrochemical corrosion. Studies have shown that industrial water, whether fresh water or sea water, will have a variety of ions and dissolved oxygen, in which chlorine ion and oxygen concentration changes, the corrosion shape of metal plays an important role. In addition, the complexity of the metal structure will also affect the corrosion morphology. Therefore, the corrosion of welded seams between tube plate and tube is mainly caused by hole corrosion and slot corrosion. From the outside, there are many corrosion products and deposits on the surface of tube plate, which are distributed with pits of different sizes. When using seawater as a medium, galvanic corrosion will also occur. Chemical corrosion is the corrosion of the medium, heat exchanger tube plate contact with a variety of chemical media, will be corroded by the chemical medium. In addition, there will be some bimetallic corrosion between the heat exchanger plate and the heat exchanger tube. Some tube plates are still in erosion of corrosive medium for a long time. In particular, fixed tube-plate heat exchanger, and temperature difference stress, tube-plate and heat exchange pipe connection is easy to leak, resulting in heat exchanger failure.

      To sum up, the main factors affecting the heat exchanger tube plate corrosion are as follows:

      (1) Medium composition and concentration: the influence of concentration is different. For example, in hydrochloric acid, the higher the concentration, the more serious the corrosion is. Carbon steel and stainless steel at a concentration of about 50% sulfuric acid