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What Is Corrosion Of Shell And Tube Heat Exchanger Parts?
Jan 25, 2018

Corrosion analysis of shell and tube heat exchanger parts

The material of shell and tube heat exchanger is mainly carbon steel, stainless steel and copper. The tube plate made of carbon steel is used as a cooler. The welding seam of the tube sheet and the tube is often corroded.Leakage into the cooling water system pollutes the environment and causes material waste.

When making shell and tube heat exchanger ,The welding of tube sheet and tube is usually by manual arc welding, and the weld shape has different degree of defects.

Such as sag, stoma, slag and so on, the distribution of weld stress is not uniform.When used, the tube sheet is generally in contact with industrial cooling water. while the impurities, salts, gases and microorganisms in the industrial cooling water will form the corrosion of the tube plate and the weld, which is what we often call electrochemical corrosion. Studies have shown that industrial water, whether fresh or seawater, has a variety of ions and dissolved oxygen.The concentration change between  chloride ion and oxygen plays an important role in the corrosion shape of metal.

In addition, the complexity of the metal structure also affects the corrosion morphology.Therefore, the corrosion of tube plate and tube weld is mainly caused by hole erosion and crevice corrosion.

Viewed from the outside, the surface of the tube will have a lot of corrosion products and sediment, and a pit with unequal size.When the seawater is medium, it also produces galvanic corrosion.

Chemical corrosion is the corrosion of the medium,the heat exchanger tube plate contacts various chemical media,it will be corroded by the chemical medium.

Besides, the heat exchanger tube plate will also produce a certain bimetallic corrosion between the heat exchange tube.

Influence factor

To sum up, the main factors affecting the corrosion of shell and shell heat exchanger are as following:

1.Dielectric composition and concentration: the influence of concentration varies. For example, in hydrochloric acid, the larger the concentration, the more serious the corrosion.The corrosion of carbon steel and stainless steel is the most serious in the concentration of sulfuric acid, which is about 50%, and when the concentration increases to over 60%, the corrosion decreases sharply.

2.Impurities: harmful impurities include chloride ions, sulfur ions, cyanide ions, ammonia ions, etc. These impurities can cause serious corrosion in some cases.

3.Temperature: corrosion is a kind of chemical reaction, each ascending temperature 10 ℃, the corrosion speed of about 1 ~ 3 times, but there are exceptions

4.Ph value: the smaller the general ph value, the greater the corrosion of the metal.

5.Flow rate: in most cases, the greater the flow rate, the greater the corrosion.

Anticorrosive protection

In view of the anti-corrosion problem of cooling tower, the traditional method is mainly to repair welding, but it is easy to produce internal stress inside the tube plate, and it is difficult to eliminate, which may cause the weld of cooling tower tube sheet to leak again.

Nowadays, the western countries adopt the method of polymer composite material to protect.

Its excellent viscosity and temperature resistance, chemical corrosion resistance,it is safe to use in closed environment without shrinkage, especially good isolation bimetallic corrosion and erosion resistance, fundamentally eliminate the corrosion and leakage of repair parts provides a protective coating for cooling tower.