Plate Heat exchanger manufacturer, industry solution expert

Preventing the aging of the rubber pads of plate heat exchangers can start from the selection of materials_

by:DIGUANG     2021-03-30
Preventing the aging of the rubber pads of the plate heat exchanger can start from the selection of materials

2019-02-26 10:51
795 prevent the aging of plate heat exchanger rubber pads can start from the selection of materials, plate heat exchanger rubber gasket/seal gasket material, detachable plate heat exchanger leaks when in use, the reason is except for plate corrosion, The failure of the gasket material of the plate heat exchanger is also an important factor. There are mainly the following methods: when the rubber sealing gasket material is in contact with fluid, when a certain fluid component penetrates into the rubber, the soluble substances in it can sometimes be extracted, resulting in the swelling of the rubber gasket; the presence of halogen and the effect of ozone make The gasket becomes soft or causes stress corrosion cracking. Under certain conditions, especially at high temperatures, elastic materials will decompose and release chemical substances, and these substances themselves will corrode the plate material, such as FPM rubber will release oxygen. After disassembling the plate heat exchanger, it was found that the surface of the cold fluid end of the plate was bright, and there were a small amount of black dirt locally, the number of corrosion pits was small and did not penetrate, and there were black deposits in the corrosion pits, so it can be inferred to be a gasket Sheet corrosion exists. Fluid pressure: Leakage occurs when the detachable plate heat exchanger is used within the rated working pressure. In addition to the quality factors in the manufacturing and assembly of the equipment, it is mainly related to the abnormal impact load of water hammer and air hammer in the system. This is a phenomenon that is not easy to observe during use. The instantaneous pressure peak caused by the impact is often 1-3 times higher than the normal working pressure, which displaces the rubber gasket installed in the plate heat exchanger and causes the seal to fail [2]. Since the heat transfer element of this kind of equipment is made of stainless steel sheet (thickness 0.5-1.0mm), its sealing rigidity is relatively poor and the sealing periphery is very long, so the impact pressure resistance ability is much lower than that of the shell-and-tube heat exchanger. This abnormal impact of the plate heat exchanger can be judged based on the equipment that provides the conveying medium for it. During the maintenance of the alkali pump that transports the lye to the plate heat exchanger, it is found that there are a small amount of honeycombs in the pump casing, indicating that the pump is in operation There is cavitation; at the same time, because of the leakage around the plate in the early stage, it can be inferred that the change of fluid pressure is also a possible factor of leakage. Temperature: Rapid changes in temperature can also cause seal failure. When the temperature changes too fast, the linear expansion coefficient of the rubber gasket does not match the elastic deformation and the sealing pre-tightening force, which will reduce the sealing pre-tightening force and cause the pressure capacity of the equipment to be lower than the rated design pressure. Judging from the working conditions of the plate heat exchanger, the temperature has little effect on it, so it can be ruled out. Corrosion: The corrosion of the plate heat exchanger mainly refers to the corrosion of the plates. Plate heat exchangers are mostly made of stainless steel sheets. Although stainless steel has excellent corrosion resistance, it will cause uniform or local corrosion of the stainless steel plates after the passivation film is destroyed. Most of the corrosion phenomena exhibited by plate heat exchangers are stress corrosion caused by Cl-, which often occurs at the bottom of the plate seal groove and the bottom of the scale after the formation of dirt. The main reason is that the stainless steel plate is made by mechanical cold stamping. , A certain amount of residual surface stress will inevitably remain. For stainless steel sheets without molybdenum, it is very difficult to eliminate the residual stress on the surface. After the plates are assembled, a multi-slit structure is formed, and the corrugated tops of adjacent plates cross each other to form a large number of contacts. There will be gaps in the cross contacts, and the medium in the gaps will not flow smoothly, so that there will be a difference in oxygen concentration inside and outside the gaps, which will cause crevice corrosion. When the dirt on the surface of the plate is serious, the corrosive elements (Cl, S, etc.) in the medium may adhere to the dirt in a large amount and be enriched in the cracks at the bottom of the dirt. The harmful elements in the bottom of the sealing groove are often precipitated out of the Cl in the adhesive due to the instability of the temperature rise. Such as the neoprene series of adhesives and compressed asbestos mats (containing CaCl2), often under water and steam conditions, the precipitated enriched Cl- and H+ form H Cl, causing serious stress corrosion at the bottom of the groove Cracked. When inspecting the disassembled plates, it was found that most of the plates at the inlet of the thermal fluid side had cracks, and there was a thick layer of dark brown deposits before cleaning; the top of the herringbone corrugations on the inlet side of the thermal fluid were adjacent to each other. The contacts at the top of the herringbone corrugated plates have dotted surface damage and corrosion spots, and there are dark brown deposits around them. There are 1 to 2 perforation corrosion on each plate, all of which are on the cross contacts at the top of the corrugation near the inlet side of the hot fluid. Corrosion pits and pits are formed in local areas.
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