What factors affect heat exchanger corrosion
There are many factors affecting the corrosion of plate heat exchangers, which there are two main factors:
1.Effect of heat transfer on corrosion
The corrosion behavior of metals is different under the conditions of heat transfer and no heat transfer. In general, heat transfer exacerbates the corrosion of metals, especially under conditions of boiling, vaporization or overheating. The effects of heat transfer are different in different media and metals.
2.Effect of cooling medium on metal corrosion
(1) Dissolved Oxygen Dissolved oxygen in water is an oxidant that participates in the cathode process, so it generally promotes corrosion. When the concentration of oxygen in the water is not uniform, a concentration cell of oxygen will be formed, causing localized corrosion. For carbon steels, low alloy steels, copper alloys and certain grades of stainless steel, melting oxygen is the most important factor affecting their corrosion behavior in water.
(2) Other dissolved gases CO2 will cause corrosion of copper and steel when there is no oxygen in water, but does not promote corrosion of aluminum. Trace amounts of ammonia corrode copper alloys but have no effect on aluminum and steel. H2S promotes corrosion of copper and steel, but has no effect on aluminum. SO2 reduces the pH of the water and increases the corrosivity of the water to the metal.
(3) Hardness Generally speaking, the hardness of fresh water is reduced to corrosion of metals such as copper, zinc, lead and steel. Very soft water is very corrosive. In this water, it is not suitable to use copper, lead and zinc. In contrast, lead is resistant to corrosion in soft water and pitting corrosion in high hardness water.
(4) Effect of ions Chloride ions can damage the surface of passivated metals such as stainless steel and induce pitting or SCC.
(5) Effect of scale CaCO3 scale in fresh water. The CaCO3 scale layer is detrimental to heat transfer, but is beneficial for preventing corrosion.
(6) PH Value The corrosion of steel in water with a pH > 11 is small, and the corrosion increases at pH < 7.