What are causes of corrosion in plate heat exchangers?
(1) The harmful elements in the bottom of the sealing groove are often precipitated by Cl- in the binder due to an increase in temperature. For example, the neoprene series of adhesives and compressed asbestos (containing CaCl2) tend to form HCl in the enrichment of Cl- and H+ under water and steam conditions, causing severe stress corrosion cracking at the bottom of the groove. Under the conditions of residual stress on the surface, enrichment of Cl- and temperature, the stress corrosion cracking may occur after a certain corrosion incubation period. Trying to destroy any of the above conditions during the selection, installation and use of the plate heat exchanger can effectively prevent or delay the occurrence of corrosion and enable the equipment to operate safely and normally. For this reason, the correct selection of materials, regular descaling to destroy the formation conditions and incubation period of corrosion, the use of non-chlorine adhesives, which can effectively prevent stress corrosion to a certain extent.
(2) When the fouling on the surface of the plate is serious, the corrosive elements (Cl, S) in the medium may attach to the fouling in large quantities and accumulate in the gap at the bottom of the scale
(3) After the heat exchanger plate is assembled, a multi-slit structure is formed, such as a contact ponit between the plates, the bottom of the sealing groove. The gap is easy to cause the enrichment of Cl-, and the degree of local enrichment often far exceeds the ability of stainless steel itself to resist stress corrosion.
(4) The stainless steel heat transfer plate is mechanically stamped and inevitably retains a certain amount of surface residual stress. For stainless steel sheets without molybdenum, the elimination of surface residual stress is difficult or even impossible.