Corrosion and protection measures of stainless steel plate heat exchanger, plate heat exchanger is a heat exchanger made of a series of metal sheets with a certain corrugated shape. Thin rectangular channels are formed between various plates, and heat is exchanged through the plates. Plate heat exchanger is an ideal equipment for liquid-liquid and liquid-vapor heat exchange.
With the continuous expansion of the field of use and the advancement of manufacturing skills, people's knowledge of the advantages of plate heat exchangers has gone further, which has promoted the use of plate heat exchangers in China. Now it has been widely used in various fields, so avoiding or slowing down the corrosion of plate heat exchangers is an urgent imperative for us. The study and use of anti-corrosion questions are of great significance to avoid premature damage of plate heat exchangers, reduce waste of resources caused by corrosion, reduce unnecessary shutdowns and the resulting loss of goods.
The corrosion of stainless steel plate heat exchanger mainly refers to the corrosion of the plate. Common corrosion is divided into pitting corrosion, crevice corrosion, stress corrosion, wear and abrasion corrosion and other types.
1. Corrosion scene
(1) The stainless steel heat transfer plate is made by mechanical stamping, and inevitably a certain amount of residual surface stress remains. For stainless steel sheets without molybdenum elements, it is very difficult to eliminate the residual surface stress, or even impossible.
(2) After the plates are assembled, a multi-slot structure is formed, such as the contacts between the plates and the bottom of the sealing groove. The crevices simply form the enrichment of Cl-, and the degree of partial enrichment usually far exceeds the ability of the stainless steel itself to resist stress corrosion.
(3) When the dirt on the surface of the plate is severe, many corrosive elements (Cl, S, etc.) in the medium may adhere to the dirt and accumulate in the crevices at the bottom of the dirt.
(4) The harmful elements in the bottom of the sealing groove are usually separated from the Cl- in the binder due to the increase in temperature. Such as neoprene series of adhesives, compressed asbestos (rich in CaCl2), usually under the conditions of water and steam, the separated enriched Cl- and H+ form HCl, which causes severe stress corrosion at the gap at the bottom of the tank cracked. Under the conditions of surface residual stress, Cl- enrichment degree and temperature, through a certain corrosion incubation period, stress corrosion cracking may occur in plate crevices. Trying to damage any of the above conditions during the selection, installation and use of the plate heat exchanger can effectively avoid or delay the onset of corrosion and enable the equipment to operate normally. To this end, accurate selection of materials, regular cleaning to damage the formation conditions and incubation period of corrosion, and selection of non-chlorine adhesives can effectively avoid stress corrosion to a certain extent.
2. Corrosion protection measures for stainless steel plate heat exchangers
(1) First of all, the ability of the material to engage in medium corrosion should be considered, and the plate material should be selected accurately.
(2) The surface of the stainless steel sheet is passivated to form a firm, dense and very thin film on the surface of the oxide film, thus obtaining excellent corrosion resistance.
(3) When planning the forming die of the plate, the structure with small residual stress should be selected.
(4) In order to reduce the scratches on the surface of the plate, the surface of the mold should be polished.
(5) Do not use expired and chlorine-rich adhesives for the adhesives between plates and gaskets.
(6) Select accurate and reasonable plate structure and normal flow rate.
(7) Increase the contact rate of the plate contacts to reduce the damage to the contacts.