In a heating system, the plate heat exchanger acts like an engine responsible for transferring and distributing thermal energy, continuously moving heat from one side of the system to the other.
But have you ever encountered any of these problems?
Heat transfer efficiency suddenly drops for no obvious reason?
The outlet water flow becomes slower and slower?
You open the heat exchanger and find that some plates have become discolored, blackened, or even blistered?
If so, you may be dealing with corrosion inside the plate heat exchanger.
This is not a minor problem. If corrosion is not repaired properly, heat transfer performance can continue to decline. In serious cases, it may lead to fluid leakage, system contamination, or even equipment rupture and unplanned shutdowns.
So today, let's take a closer look at one important question:
Once corrosion occurs in a plate heat exchanger, how should it be repaired properly? And what can be done to prevent the same problem from happening again?
I. First, Understand the Cause: Why Do Plate Heat Exchangers Corrode?
Before deciding how to repair a problem, you need to understand what caused it.
Why does a plate heat exchanger corrode? In most cases, the root causes fall into the following three categories.
1.1 Corrosion Caused by the Fluid
Some systems use water or other fluids containing corrosive substances such as chloride ions, sulfides, and organic acids.
When these substances remain in contact with stainless steel plates for a long period of time, they can gradually attack the metal surface and eventually cause serious corrosion.
It is similar to how continuous exposure to acidic drinks can gradually damage tooth enamel. Over time, the material becomes weaker and more vulnerable to damage.
1.2 Electrochemical Corrosion
Electrochemical corrosion is particularly likely to occur when different metals are in contact with each other in a conductive water environment.
The difference in electrical potential between the metals causes a small electric current to flow, creating an anode and a cathode and resulting in galvanic corrosion.
A simple example is placing iron and copper in water. Over time, the iron becomes the metal that is preferentially attacked, leaving pits and uneven damage on its surface.
1.3 Localized Pitting or Crevice Corrosion
When deposits, scale, or stagnant areas exist inside a heat exchanger, they can create localized micro-environments.
These areas may develop higher concentrations of corrosive substances, resulting in localized corrosion, particularly pitting or crevice corrosion.
In other words, corrosion is rarely caused by a single factor. It is often the combined result of long-term exposure, improper material selection or system design, and insufficient maintenance.
II. What Should You Do When Corrosion Occurs? 5 Common Repair Methods Explained
If corrosion is irreversible, can a corroded plate heat exchanger still be repaired?
Yes, it can-but the right repair method must be selected according to the extent and type of corrosion.
Below are five common approaches used by professional maintenance technicians, along with their main advantages, disadvantages, and suitable applications.
2.1 Replace the Corroded Plates - The Most Direct and Effective Option
Principle:
Remove the severely corroded plates and replace them with new plates of the same model or with properly specified replacement plates.
Advantages:
Provides a thorough repair and can restore the equipment to good operating condition
Maintains the original structure and performance of the heat exchanger
Disadvantages:
Relatively high cost, especially when stainless steel or titanium plates are required
Replacement plates may be difficult to source if the heat exchanger model is old or discontinued
Suitable for:
Localized corrosion involving individual plates, particularly when only a small number of plates are damaged and the repair budget is sufficient.
2.2 Localized Metal Spray Repair
Principle:
Apply a protective metal or ceramic coating to the corroded area to form a barrier against further corrosion.
Advantages:
Allows localized repair without replacing the entire plate
Moderate cost and relatively quick results
Disadvantages:
Coating adhesion may be limited, making it unsuitable for long-term service in some applications
May slightly reduce heat transfer efficiency
Suitable for:
Minor surface corrosion, temporary emergency repairs, or situations where the equipment needs to remain in service for a short period.
2.3 Apply an Anti-Corrosion Coating
Principle:
Apply a corrosion-resistant coating, such as a fluorocarbon or epoxy coating, over the affected surface.
Advantages:
Simple to apply
Relatively low cost
Can slow down further corrosion
Disadvantages:
Coating thickness may affect heat transfer efficiency
Coatings can peel or deteriorate over time, and their durability is generally limited
Suitable for:
Preventing corrosion from spreading, particularly on standby equipment or non-critical heat transfer sections.
2.4 Welding Repair and Polishing - Only for Localized, Non-Perforating Corrosion
Principle:
Use specialized micro-welding techniques to fill localized corrosion pits, followed by grinding and polishing to restore the surface.
Advantages:
A relatively low-cost option for extending service life
Preserves the original plate structure and can reduce equipment downtime
Disadvantages:
Not suitable for extensive corrosion or plates that have already been perforated
Requires highly skilled welding technicians and precise workmanship
2.5 Replace the Entire Heat Exchanger - For Extensive Corrosion or Equipment Near the End of Its Service Life
When multiple plates have been seriously corroded, the gaskets have also deteriorated, and heat transfer performance has declined significantly, the cost of continued repairs may no longer be worthwhile.
In this situation, replacing the entire heat exchanger may be the better option.
A new heat exchanger can help:
Reduce the risk of equipment failure
Improve system efficiency
Avoid the recurring costs and downtime associated with repeated repairs
III. Prevention Is Always More Important Than Repair: 6 Practical Recommendations
If you do not want to repeat the same heat exchanger repair cycle every year, plant managers and maintenance teams should pay close attention to the following six measures.
It is recommended to disassemble and inspect the heat exchanger at least once a year.
If rust spots, pitting, or other signs of corrosion are found, they should be addressed as early as possible.
Control the chloride concentration, pH value, and hardness of the incoming water.
Where necessary, install appropriate water treatment equipment to maintain water quality within the required operating range.
Sudden changes in temperature and pressure can accelerate corrosion and contribute to gasket failure.
The heat exchanger should therefore be started up and shut down gradually, avoiding sudden changes in operating conditions.
Do not use strong acids indiscriminately when cleaning the heat exchanger.
Use a suitable inhibited cleaning solution designed for heat exchanger maintenance, and make sure any remaining cleaning solution is properly neutralized after cleaning.
Aged or deteriorated gaskets can allow moisture and contaminants to enter and accumulate in localized areas, which may accelerate corrosion.
Replace damaged or aged gaskets promptly to maintain proper sealing and protect the plates.
A heat exchanger that is shut down and kept in standby storage still requires proper protection.
Keep the equipment properly sealed and protected from moisture to reduce the risk of corrosion and oxidation during extended periods of non-use.
Final Summary: Don't Wait Until You See Rust to Take Action
Corrosion in a plate heat exchanger is not simply a matter of "one piece of metal getting rusty." It can indicate a much larger problem.
What you may lose is:
Heat transfer efficiency across the entire unit;
Higher energy consumption and greater operating risks throughout the system;
And potentially, the trust of your customers in your production facility.
So, when corrosion occurs, don't panic. Choose an appropriate repair method based on the actual condition of the equipment.
And even if your heat exchanger shows no obvious signs of corrosion, don't let your guard down. Follow a regular inspection and maintenance schedule.
A well-maintained plate heat exchanger can do more than simply extend equipment life. Proper maintenance can help prevent costly failures, reduce repeated repair expenses, and keep the system operating reliably for years to come.
