The plate heat exchanger is composed of a set of corrugated metal plates with four corner holes for the two liquids to pass through. The metal plates are installed in the frame of the fixed plate and the movable compression plate, and are clamped by clamping bolts. The commonly used materials of plate heat exchanger plates are generally 304, 316L, SMO-254, titanium plate, nickel plate and Hastelloy. The choice of plate material for the heat exchanger mainly depends on the characteristics of the medium. Common water, soda, oil and water use 304 or 316L. Why does the water, soda, and oil-water heat exchanger plates also corrode?
In the case of plate corrosion, if it is not a selection error, we must consider that stress corrosion will occur if the water contains chloride solution. This is because the chloride ions in the water damage the passive film on the surface of the stainless steel. Under the action of tensile stress, cracks will occur in the damaged area of the passive film, which is called the anode area of the corrosion battery. The continuous electrochemical corrosion may eventually lead to the perforation of the heat exchanger plate.
Many customers believe that the chloride ion content in the water is not high and has no effect on the heat exchanger plates. Even a small amount of chloride ions may cause stress corrosion. In actual production, some equipment is not damaged by corrosion under normal operating conditions, but stress corrosion cracking occurs due to the low concentration (5%) chloride condensate remaining in the heat exchanger during shutdown. There is also a pressure test with water with a high concentration of chloride ions, and the water remaining in the plate heat exchanger is concentrated to produce stress corrosion.