Case Analysis of Plate Heat Exchanger Leakage

According to the common leakage reasons of the plate heat exchanger, combined with the leakage condition of the plate heat exchanger in the actual device (observing the leakage situation and checking the pressure test results of the leakage plate heat exchanger) and the working conditions, the causes of the leakage are analyzed and the improvement is proposed. Suggest.

Introduction to working conditions

In this example, the device is a fully welded plate heat exchanger.

Usage description

The heat exchanger effect of the plate heat exchanger is significantly reduced after use. And internal leakage occurs, the corrosion of the heat exchanger bottom plate appears obvious, the leakage situation after disassembly and the leakage situation after the observation of the pressure test have the following characteristics:
The overall fouling of the cold medium process is serious, especially the fouling of the flow passage in the outlet part;

After the pressure test on the inlet side and the outlet side of the cold medium process, it is found that there is no leakage point at the inlet end, the leakage point is mainly concentrated at the outlet end, and the leak point is distributed above the liquid boundary line;

There is no leakage at the welded joint (weld seam), and the leakage point is concentrated on the base material near the weld end and is irregularly distributed;

Leakage analysis

The plate heat exchanger is seriously fouled. Because the plate heat exchanger makes the water quality not up to standard, it may contain excessive levels of chloride ions, calcified salts, sludge micro-particles, etc., and the water treatment in the system is not enough, due to the high temperature of the heat medium inlet. The circulating water is rapidly heated at the inlet of the heat medium, which is beneficial to the scaling environment. After use, the scale is quickly scaled to make the flow channel smaller or block the flow channel. The cold medium becomes smaller due to the smaller flow path, and the flux is reduced. The area is reduced, the heat exchange effect is also greatly reduced, and the outlet tube box is vapor-liquid mixed. The vapor body cannot be discharged within a certain period of time, and two vapor-liquid chambers appear, and a vapor-liquid mixed corrosion layer appears on the boundary liquid surface.

Due to the poor quality of the cooling water used in the plate heat exchanger and the high content of chloride ions in the water, the corrosion resistance of the stainless steel against pitting, crevice corrosion, stress corrosion and corrosion is reduced, and pitting, crevice corrosion and stress corrosion are prone to occur. In turn, the plate is corroded and perforated or the plate has cracks, which eventually causes the plate heat exchanger to leak;

Combined with the pressure test results, there is no leakage point at the inlet of the cold medium (the outlet end of the heat medium), and the leakage point is mainly concentrated at the outlet end of the cold medium (the inlet end of the heat medium), so it is judged that the selection of the plate heat exchanger and the equipment manufacturing and installation welding Seam quality and gasket problems are not the cause of the leak;

Because the inlet temperature of the heat medium is high, it enters the gas phase. When it exchanges heat with the partition wall of the cold medium, there are physical conditions of cavitation in the contact part between the cold medium and the wall, and the corrosion caused by cavitation is not excluded.

In summary, combined with the common causes of plate heat exchanger leakage, it is concluded that the main cause of leakage of the plate heat exchanger is that the water quality is not up to standard, resulting in serious scaling on the outlet side of the plate heat exchanger, which causes corrosion leakage.

improve proposals

Based on the above analysis, improvements and preventions can be made from the following aspects.

Since the water quality is not up to standard is the root cause of leakage of the plate heat exchanger, it is necessary to strictly control the water quality during operation, strengthen the filtration of the water entering the system (requires regular cleaning of the filter) and conduct water quality testing to control the content of related ions. After passing the test, it can enter the heat exchange system;

The device is a fully welded plate heat exchanger, which is inconvenient to clean after scaling. It can be replaced by optional detachable plate heat exchanger according to the relevant process conditions, which is convenient for cleaning; however, the detachable plate type is replaced. The weakest link of the heat exchanger is the sealing gasket, so the gasket should be selected with reasonable structure and reliable quality, and it can be prevented during installation and use;
Analyze the working conditions of each plate heat exchanger in the device, optimize the conditions that easily cause leakage of the plate heat exchanger or replace other types of heat exchangers (such as shell-and-tube heat exchangers or tube-and-tube type) Heat exchanger, etc.) ;  

Different precautions were developed for each working condition of each plate heat exchanger.