Corrosion Common in Heat Exchanger Units

Corrosion of heat exchanger units is a common phenomenon. The phenomenon and mechanism of metal corrosion are more complex, and the scope involved is very wide. According to the reaction mechanism, metal corrosion can be divided into two categories of chemical corrosion and electrochemical corrosion. According to the appearance of corrosion characteristics, metal corrosion can be divided into two categories of comprehensive corrosion and local corrosion. Below we introduce several common corrosion phenomena of heat exchanger units.

Here is the content list:

• Causes

• Local erosion of the inner wall of the waterside pipe

• Pitting and pore corrosion of the inner wall of the water side of the tube

• Stress corrosion rupture

 

Causes

Refrigeration unit heat exchanger tube corrosion causes impure water quality, atmospheric pollution of water, tube wall conditions and the size of the water flow rate, heat transfer surface temperature gradient size, and other factors are closely related. Due to the presence of tube wall scaling adherents, there is often local erosion and pitting of the inner wall of the tube.

Local erosion of the inner wall of the waterside pipe

When the cold water (or cooling water) containing dirt, air (dissolved with SO2), and sulfite gas flowing rapidly through the tube, will break through the tube on the surface of a layer of corrosion-resistant protective film. Such as the copper tube protective film stripped the surface, due to the low concentration of copper ions, anode, and cathode of the electrochemical corrosion. Produce such corrosion on the inner surface of the copper tube showing fish scale pit concave and with small spots. When there is no foreign body attached to the tube wall of the heat exchanger unit, the corrosion pits deepen in the direction of water flow.

Pitting and pore corrosion of the inner wall of the water side of the tube

The heat exchanger unit of the water side of the tube corrosion is mostly in the case of scale or other adhesions are not uniformly covered. For copper and its alloys, its corrosion in water is the result of the destruction of the oxide film, the uneven inflation cell caused by scaling is often the main reason for the destruction of the surface film. For example, when cold water or cooling water contains a certain content of copper ions, it will produce a small battery, so that per ions plated on iron and produce pitting and hole corrosion phenomenon, that is, copper plating phenomenon. Whether it is pitting corrosion or hole corrosion, can make the copper tube 1 to 2 years to penetrate. This causes corrosion of the heat exchanger unit for a long time and is not easy to repair.

Stress corrosion rupture

Such as a brass heat exchanger unit in some ordinary environment (such as water, water vapor, or atmosphere), the stress state may produce stress corrosion rupture. In addition, ammonia is the corrosive agent that makes copper alloy rupture. For brass, its rupture resistance increases with the copper content. Such as 85% copper content of brass 65% copper content has a better resistance to rupture performance. Brass heat exchanger unit in stress mostly from the residual stress generated by cold processing.

These are a few common heat exchanger unit corrosion situations. We have introduced the characteristics of each type of corrosion from the causes and effects respectively. Only by understanding the characteristics of each corrosion, we can better avoid the corrosion phenomenon of heat exchanger units.