Prevention of failure of stainless steel heat exchanger

Prevention of failure of stainless steel heat exchanger

Stainless steel heat exchangers are widely used in petroleum, chemical and other industries. There are several common failures:

　　 1. External leakage, mainly due to failure of the plate seal. According to literature, many thermal power stations in Beijing, Qinghai, Xinjiang and other places have high steam temperature, and rubber gaskets fail at high temperatures, causing steam to leak.

　　2, string liquid. Because the use temperature is far beyond the application range of the material, the medium in the plate flow channel on the higher pressure side is strung into the flow channel medium on the lower pressure side. The plate heat exchanger using saturated steam as the heat source, when the steam temperature is too high, it is prone to steam leakage during operation and rapid condensation in the sealed areas on both sides of the plate, and the condensed residual liquid continues to accumulate to form a local Cl- mass concentration Higher, the passivation layer on the surface of the plate is destroyed, and the internal stress caused by the cold stamping of the plate at this place is relatively large, causing stress corrosion and causing liquid leakage.

　　 3. The pressure drop is too large. Excessive dirt in the medium causes fouling on the surface of the plates, which causes the flow velocity of the flow passage between the plates to be too high, and the pressure drop exceeds the allowable range.

　　To improve the corrosion resistance, we can mainly start from two aspects,

　　 One is to improve manufacturing quality,

　　 The second is to try to avoid or control the contact of chloride ions with the shell. To control the contact of chloride ions with the shell, isolation is mainly used.

　　 At present, my country mainly uses non-metallic anti-corrosion coatings for isolation. Commonly used in pressure vessels are lacquer, epoxy paint, etc., because these non-metallic materials have strong adhesion, tough paint film, wear resistance, temperature resistance, and low cost, so they are not only convenient to use, but also can greatly improve the heat exchange of stainless steel. The performance of the device. By comparison, it is found that the heat exchanger made of 316 stainless steel has a higher chloride ion content in the environment (water), but no corrosion has been found in the inspection so far. Therefore, s* should first choose stainless steel with better pitting resistance as the shell material, such as 316 or 316L. As the 18-8 stainless steel is added with 2% Mo, its corrosion resistance is greatly increased. When welding, try to use argon arc welding instead of arc welding. On the basis of ensuring the quality of weld fusion, the welding process parameters should be strictly controlled, and the method of small heat input and multi-pass welding should be adopted to avoid local overheating of the weld.　　

　　 The sealing surface itself has a high residual stress of cold working, and there is a high stress level under the operating conditions, which is the direct cause of the failure of the heat exchanger plate. Elements such as C1 and S contained in neoprene are precipitated at the operating temperature, leading to stress corrosion of austenitic stainless steel, which is the root cause of the failure of the heat exchanger plate. It is recommended to periodically check the above parameters during use to avoid similar accidents.