(1) The stainless steel heat transfer plate is formed by mechanical stamping, and a certain amount of residual surface stress is inevitably left. For stainless steel sheets that do not contain molybdenum, it is difficult or even impossible to eliminate residual surface stress.
(2) After the plates are assembled, a multi-slit structure is formed, such as the contacts between the plates and the bottom of the sealing groove. The gap is easy to cause the enrichment of Cl-, and the local mass fraction can reach tens of thousands of 10-6, which far exceeds the ability of stainless steel to resist stress corrosion.
(3) When the fouling on the surface of the plate heat exchanger is serious, the corrosive elements (Cl, S) in the medium may be attached to the fouling in large amounts and be enriched in the cracks at the bottom of the fouling.
(4) The harmful elements in the bottom of the sealing groove are often precipitated out of the Cl in the adhesive due to temperature rise. Such as the neoprene series of adhesives and compressed asbestos pads (containing CaCl2), under the conditions of water and steam, the precipitated enriched Cl- and H+ form HCl, causing serious stress corrosion cracking at the bottom of the groove.