Causes of leakage of heat exchange tubes

 Shell & tube heat exchanger is one of the process equipment used in chemical and petrochemical production equipment. In the heat exchanger equipment, the refrigerant or carrier refrigerant and the cooling medium exchange heat through the seamless heat exchanger tubes. The low-temperature medium absorbs the heat of the cooled object and evaporates into low-pressure steam. The high-temperature steam is released into the cooling medium in the heat exchanger to be heated and condensed into a high-pressure liquid, thereby forming a closed-loop heat exchange process.

 

In the process of many chemical heat exchanger projects, the difficult problem we encountered was the leakage of heat exchange tubes. The main reason for the leakage and failure of the heat exchange tube is that the copper and carbon steel in the heat exchanger have some sulfide ions, chloride ions and corrosive elements. Moreover, the high temperature phenomenon and scale phenomenon in the heat exchange tube will also have a greater impact, causing leakage from the perforation. Below we will analyze the causes of heat exchange tube leakage:

 

1. The influence of working temperature

The leakage of the heat exchanger is mainly caused by a small number of openings on the surface of the heat exchange tube. If you scratch and retain some accessories on the outside of the tube, you can find that the main reasons for this phenomenon are:

 

①Due to the difference of heat exchanger conditions and working temperature, the temperature is relatively high during operation. This will cause the temperature of the scale layer of the heat exchange tube to continue to rise, leading to local vaporization areas and conditions that produce acidic media;

 

②In the later stage of process water evaporation, some alkaline substances are evaporated, which will convert the evaporation of process water into acidic substances.

 

2. The influence of water quality PH value

The PH value of the process water was researched and inspected, and the PH value produced was observed and analyzed. Comparing the pH value of the process water before and after evaporation, it can be found that when the pH value is 8.58.8, the corrosion rate of copper is low, while the pH value of carbon steel is above 9.5. The pH value of the water is too high, leading to corrosion of the copper tube. The main factors affecting the corrosion of the carbon steel heat exchange tube are: oxygen content and pH of the feed water. When the dissolved oxygen in the feedwater is too high or the pH value is too low, the inner wall of the heat exchange tube will deteriorate and corrode. Oxygen will cause oxygen corrosion on the outer wall of the tube bundle.

 

3. Erosion and erosion

When the steam flow in the heat exchanger is high and the steam flow contains large water droplets, the outer wall of the tube is scrubbed and thinned due to the two-phase flow of steam and water, resulting in pressure perforation or rupture, and two-phase steam and water are generated inside the heat exchanger The main reason for the flow:

 

①The steam inside and outside the superheated steam cooling section cannot reach the superheat required by the design;

②When the outlet water level of the heat exchanger remains too low and the outlet water temperature is much higher than the design temperature, flashing may occur. When the outlet water enters the next-stage heat exchanger, steam will be generated, which will be affected by impurities in the cleaning water.

 

In many cases of leakage, it is usually found that there are a large number of large particles of sand, shells and the like in the heat exchanger. The main reason is that in actual use, there is a large amount of sea water or sewage that is directly processed without treatment. It is transported to the inside of the heat exchanger and flows continuously in the heat exchange tube, which can easily cause scratches or abrasion on the heat exchange tube. In addition to affecting the heat exchange effect, the time of the heat exchanger is also greatly reduced, making the original heat exchanger thinner. The heat pipe ruptured prematurely, causing leakage.