Stress corrosion of plate heat exchanger plates
The plate heat exchanger plates are mechanically stamped and inevitably retain a certain amount of surface residual stress. For stainless steel sheets without molybdenum, the elimination of surface residual stress is difficult or even impossible.After the plates are assembled, a multi-slit structure is formed, such as a contact between the plates and a bottom portion 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.When the dirt on the surface of the sheet is severe, the intercalating corrosion elements (Cl, S) may adhere to the dirt in a large amount and are concentrated at the bottom of the scale.The harmful elements in the bottom of the sealing groove are often precipitated by the temperature rise of Cl in the binder. For example, the neoprene series of adhesives and compressed asbestos (containing CaCl2) tend to form ClCl and H+ in the water and steam conditions to form HCl, causing severe stress corrosion cracking at the bottom of the groove.