Case analysis of plate heat exchanger leakage situations

Based on common leakage causes of plate heat exchangers, combined with the leakage situation in actual installations (observing leak locations and checking pressure test results of leaking plate heat exchangers) and operating conditions, the leakage causes are analyzed to propose improvement suggestions.

 Introduction to operating conditions

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

 Description of usage 

After a short period of use, the heat exchange efficiency of this plate heat exchanger significantly decreases. Internal leakage occurs, and obvious corrosion appears on the heat exchanger base plate. After disassembly, the leak is observed and the pressure test reveals the following characteristics: 

Severe scaling in the cold medium process overall, especially at the outlet where some runners become blocked by scaling; 

After pressure testing on the inlet and outlet sides of the cold medium flow, it was found that there were no leakage points at the inlet end; the leakage points were mainly concentrated at the outlet and distributed above the liquid boundary line; 

There is no leakage at the weld joint (weld seam), and leakage points are concentrated on the base material near the weld end, forming irregular point distribution;

Analysis of the causes of the leak 

Plate heat exchangers suffer from severe scaling because the water quality is substandard, possibly containing excessive chloride ions, calcified salts, sludge particles, and other components. Additionally, insufficient water treatment in the system results in high temperature at the hot medium inlet, causing circulating water to be rapidly heated at the inlet, creating an environment favorable for scaling. After use, rapid scaling causes the flow channel to shrink or block the flow channel. The cold medium's reduced flow rate and heat exchange area decrease significantly, greatly reducing heat exchange efficiency, and steam-liquid mixing occurs in the outlet tube box. For a certain period, the gas cannot be discharged, resulting in vapor-liquid chambers and a mixed vapor-liquid corrosion layer on the boundary liquid surface; 

Because the cooling water used in plate heat exchangers is of poor quality, with high chloride ion content in the water, the resistance to pitting, crevice corrosion, stress corrosion, and corrosion fatigue is reduced, making pitting, crevice corrosion, and stress corrosion prone to occurring, which can lead to corrosion perforations or cracks in the plates, ultimately resulting in leakage in the plate heat exchanger; 

Based on the pressure test results, there is no leakage point at the cold medium inlet (hot medium outlet end), and leakage points are mainly concentrated at the cold medium outlet (hot medium inlet end). Therefore, it is determined that material selection, equipment manufacturing and installation weld quality, and sealing gasket issues are not the causes of leakage in the plate heat exchanger; 

Due to the high inlet temperature of the hot medium, the vaporized phase enters, and during heat exchange with the cold medium's interwall, physical conditions for cavitation exist at the contact area between the cold medium and the plate wall, and corrosion caused by cavitation cannot be ruled out. 

In summary, combined with the common causes of plate heat exchanger leakage, it is concluded that the main cause of leakage is substandard water quality, leading to severe scaling on the outlet side of the plate heat exchanger, which in turn leads to corrosion leakage.

 Improvement plans 

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

Since substandard water quality is the fundamental cause of plate heat exchanger leaks, strict water quality control must be maintained during operation. Water entering the system must be filtered (filters cleaned regularly) and water quality tests must be conducted to control the content of relevant ions. Only qualified individuals may enter the heat exchange system; 

The device uses a fully welded plate heat exchanger, which is difficult to clean after scaling. Depending on relevant process conditions, some suitable plate-type heat exchangers can be replaced with detachable plate heat exchangers for easier cleaning; However, the weakest link in detachable plate heat exchangers is the sealing gasket, so the gasket should be selected with reasonable structure and reliable quality, and should be prevented during installation, use, and maintenance; 

Analyze the operating conditions of each plate heat exchanger in the unit, optimize or adjust conditions prone to leakage, or choose alternative types of heat exchangers (such as shell-and-tube or shell-and-tube heat exchangers); 

Different preventive measures are developed for the different operating conditions of each plate heat exchanger.