Plate heat exchanger in the operation of the use of the period may appear corrosion problems, then, do you understand the reasons behind this phenomenon? Below by me for you to briefly explain a few of the main reasons for this situation.
Plate heat exchanger corrosion of the main reasons:
1. Because the stainless steel heat transfer plate is processed by mechanical stamping, so it will leave a certain residual stress on the plate surface. Especially for the stainless steel sheet without molybdenum element, it is very difficult to eliminate these residual stresses, and may even be impossible to realize.
2. The plate heat exchanger is composed of a combination of multiple plates, and many gaps will be formed between the plates, such as the contact points of the plates and the bottom of the sealing groove and other locations. These gaps can easily lead to the accumulation of chloride ions (Cl-), the concentration of which often far exceeds the stress corrosion resistance of the stainless steel material itself.
3. If a large amount of dirt accumulates on the surface of the plate, then the corrosive elements in the medium, such as chlorine (Cl), sulfur (S), etc., may adhere to these dirt in large quantities and further enrichment in the crevices.
4. The bottom of the sealing groove may contain harmful elements, which are usually chlorine components of the binder that precipitate at elevated temperatures. For example, with the neoprene family of bonding agents and compressed asbestos containing calcium chloride (CaCl2), the precipitated chloride ions combine with hydrogen ions to form hydrochloric acid (HCl) under water vapor conditions, leading to severe stress corrosion cracking at the bottom of the groove seams.
In response to the above main causes of plate heat exchanger corrosion, we can take the following prevention and maintenance measures to extend the service life of the equipment and ensure its normal operation:
1. Material selection
- Select stainless steel materials containing molybdenum elements to improve resistance to stress corrosion.
- Consider using alloy materials with better corrosion resistance, such as titanium alloy or nickel alloy.
2. Surface treatment:
- Heat treat or surface treat plates and sheets to reduce or eliminate residual stresses.
- Use surface coating techniques such as plating or anodizing to provide an additional layer of protection.
3. Design Optimization:
- Optimize plate sheet design to reduce gaps and dead space to reduce chloride ion enrichment.
- Use of more advanced sealing materials and structures to reduce precipitation of harmful elements.
4. Cleaning and Maintenance:
- Clean the plate heat exchanger regularly to remove the accumulation of dirt and corrosion products.
- Use chemical cleaners or high-pressure water jets for cleaning, but make sure that the cleaning agents used do not cause damage to the plate materials.
5. Media Treatment:
- Treat the working medium, such as dechlorinating or softening, to reduce the content of corrosive elements.
- Control the pH of the medium to avoid overly acidic or alkaline environments and reduce the likelihood of corrosion occurring.
6. Detection and monitoring:
- Regularly inspect plate heat exchangers for corrosion, using methods such as ultrasonic, eddy current or visual inspection.
- Monitor the chemical composition of the medium and operating conditions such as temperature, pressure and flow rate to predict and prevent corrosion.
7. Operating Procedures:
- Train operators to ensure they understand the causes of corrosion and preventive measures.
- Develop and implement proper operating procedures, including startup, shutdown, and cleaning procedures.
By implementing these preventive and maintenance measures, you can effectively reduce the risk of corrosion in plate heat exchangers, ensure their long-term stable operation, and reduce repair and replacement costs.
