Five main factors affecting the heat transfer tube sheet corrosion

Date:2020-04-14

Heat transfer leakage is the most common equipment management problem in the use of heat transfers. The leakage is mainly caused by corrosion, and a small part is due to heat transfer selection and manufacturing process defects of the heat transfer itself. There are basically two types of corrosion of the device: electrochemical corrosion and chemical corrosion. In the manufacture of tubular heat transfers, manual arc welding is generally used for the welding of the tube sheet and the tubular tubes. The shape of the weld seam has different degrees of defects, such as depressions, pores, slag inclusions, etc., and the distribution of weld stress is uneven. When in use, the part of the tube sheet is generally in contact with industrial cooling water, and impurities, salts, gases, and microorganisms in the industrial cooling water will constitute corrosion of the tube sheet and the weld. This is what we often call electrochemical corrosion.

 

Studies have shown that industrial water, whether it is fresh water or sea water, will have various ions and dissolved oxygen, and the concentration changes of chloride ions and oxygen play an important role in the corrosion shape of metals. In addition, the complexity of the metal structure will also affect the corrosion morphology. Therefore, the corrosion of the welding seam between the tube sheet and the column tube is dominated by pitting corrosion and crevice corrosion. From the outside, there will be many corrosion products and deposits on the surface of the tube sheet, with pits of different sizes distributed. Galvanic corrosion will also occur when using seawater as the medium. Chemical corrosion is the corrosion of the medium. If the heat transfer tube sheet contacts various chemical media, it will be corroded by the chemical media. In addition, the heat transfer tube sheet will also produce certain bimetallic corrosion between the heat transfer tubes. Some tube sheets have also been in the erosion of corrosive media for a long time. Especially the fixed tube sheet heat transfer, there is also the temperature difference stress, the connection between the tube sheet and the heat transfer tube is very easy to leak, causing the heat transfer to fail.

In summary, the main factors affecting the heat transfer tube sheet corrosion are:

(1) Medium composition and concentration: The influence of concentration is different. For example, in hydrochloric acid, the greater the concentration, the more severe the corrosion. Carbon steel and stainless steel have the most severe corrosion in sulfuric acid with a concentration of about 50%, but when the concentration increases to more than 60%, the corrosion decreases sharply;

(2) Impurities: Harmful impurities include chloride ions, sulfur ions, cyanide ions, ammonia ions, etc. These impurities can cause severe corrosion in some cases

(3) Temperature: Corrosion is a chemical reaction. When the temperature is increased by 10 ℃, the corrosion rate is increased by about 1 to 3 times, but there are exceptions;

(4) PH value: Generally, the smaller the pH value, the greater the corrosion of the metal;

(5) Flow rate: In most cases, the greater the flow rate, the greater the corrosion.

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