Corrosion is the progressive destruction of materials, usually metals, through electrochemical or chemical reactions with the environment.
There are two main types of corrosion: galvanic and pitting. Galvanic corrosion is the most common type of corrosion in heating systems- resulting from the interaction of two different metals in an electrolyte, such as water. While pitting corrosion is a localized form of corrosion that can cause more damage than galvanic corrosion. It is caused by the accumulation of corrosive substances, such as chloride ions, on the surface of a metal.
What Causes Corrosion In A Water Heating System?
There are several reasons that a heating system can become damaged or fail prematurely. In addition to causing high energy costs, corrosion can lead to equipment failure and lower efficiency. Fortunately, chemical and mechanical approaches can help prevent corrosion. The following briefly explains corrosion and how it affects heating and cooling systems. Ultimately, it reduces equipment efficiency, increases operating costs, and reduces the system’s lifespan.
Oversizing is a major cause of corrosion in commercial water heaters- resulting in high-velocity water circulation. The high-velocity water corrodes metal. During the process, water contains suspended solids, which drive against the metal surface. Smooth grooves and round holes result from erosion caused by turbulent water. Despite not being harmful to humans, damage to metal appliances can lead to physical failure.
What Are Ways To Control Corrosion In Hydronic Heating Systems?
Corrosion of metals in a hydronic heating system often limits its lifespan. Different metals are more or less vulnerable to corrosion, so corrosion prevention is necessary for all metals in heating systems.
It is natural for heating systems to rust over time, and the consequences, such as boiler and radiator failures, are disruptive, expensive for homeowners, and extremely challenging for installers. Understanding the causes and effects of corrosion of different metals in a system is therefore important.
- As a noble metal, copper does not rust easily. Still, when copper corrosion occurs, tiny amounts dissolve in the system’s water, leading to corrosion of other metals around the system. Flux residues or other aggressive contaminants will corrode copper partially and disperse copper into the system water.
- Dissolved copper can oxidize and cause localized corrosion on steel or aluminum surfaces within the system, such as radiators or the heat exchange surfaces in boilers. It can lead to pinholes and equipment failure.
- Copper corrodes when exposed to aerated water for the first time, but the corrosion is only slight and uniform. A passivating layer of oxide prevents further corrosion when this process takes place. Corrosion beyond this point may lead to problems.
- The type of local water can affect corrosion severity. That means that depending on the water:
- Copper corrosion may continue to damage sanitary fittings, causing green stains.
- Following short periods of use, highly localized pitting and equipment metal corrosion can eventually lead to pinhole corrosion and perforations.
Aluminum corrosion is often the factor that contributes to the end of the useful life of a heating system.
- Domestic heating systems commonly use this metal system. As a result, it finds use in manufacturing highly efficient boilers and radiators because it is highly thermally conductive, light, and reasonably priced.
- A protective oxide film coating its surface makes it resistant to corrosion. Localized corrosion can occur due to disruptions in this film caused by aggressive contaminants.
- Aluminum corrosion occurs in small, localized areas, resulting in pits on the metal surface. Metal perforations and equipment failure can result if left unchecked.
- Protective films are sensitive to both aggressive contaminants and changes in pH. Ideally, the pH of the water should be between 6.5 and 8.5 since that is the ideal pH for aluminum to prevent corrosion.
- Base-exchange softened water behaves in a corrosive manner towards aluminum. Unless a corrosion inhibitor is present in the system, it may be wise to avoid using this water.
- Mild steel corrodes quickly in water and oxygen, and copious amounts of iron oxide debris can form. This spalls off into the system’s water, disrupting valves and other moving parts and eventually settles as voluminous black sludge in radiators and heat exchangers.
- Iron oxide also creates an under-deposit corrosion reaction that self-perpetuates due to an oxygen differential. It leads to predominantly localized corrosion, commonly leading to equipment failure. It occurs because under deposit corrosion often progresses into pitting corrosion, which can quickly create perforations in metal.
- Stainless steel is an alloy that can protect itself with an effective thin oxide layer. However, aggressive contaminants can penetrate this layer to cause localized corrosion, pitting, and eventual perforation.
What Will Help Control Corrosion In A Heating System?
Some problems may arise with heating systems after several years of use:
- Radiators that do not heat up
- Strange gurgling noises from the boiler
- The dark liquid inside the system
- Feels cold in the lower radiator parts.
Therefore, it is necessary to take appropriate preventative measures to avoid these problems caused by corrosion.
Adding a corrosion inhibitor to your water will help protect your system’s metal components against oxidation. While dissolved calcium and magnesium are completely harmless to human health, they can cause damage to the inside of a heating system. Calcium carbonate becomes solid when the water containing these salts is heated and turns into a solid called scale. When this scale forms, a chemical reaction occurs, creating carbonic acid, which damages metal parts. Carbonic acid is another common culprit in corroding heating systems.
Water’s unique properties make it a particularly good candidate for corrosion. Iron and steel pipes, for example, rust when exposed to oxygen and water. In addition, water contains impurities that can affect internal components. In addition, water is also subject to galvanic corrosion, caused when different metals come into direct contact with each other. In this case, you can take precautions by installing insulating couplings and coatings on your pipes and other components.
Why Is Hot Water More Corrosive Than Cold?
When a heating system uses hot water to heat the home, the higher temperature increases the ion concentration in the water and makes it more corrosive. As water temperature increases, corrosion rates increase, doubling for every 20°F increase. That makes chilled water systems more corrosion-resistant. To make them corrosion-free, designers should ensure the system is almost completely void of dissolved oxygen.
Corrosion under insulation is a common concern in heating systems. While soft foam and fiberglass insulation protect pipes from moisture and heat, they also allow for significant heat transfer. The insulation choice reduces heat transfer and prevents humidity from migrating through the system. However, most cold water piping is either insufficiently insulated or of the wrong type, and if it’s damaged, moisture can easily migrate between the pipe and the environment.
Iron is less noble than hydrogen and, therefore, more corrosive than oxygen. The iron in the water replaces hydrogen ions and forms a corrosion product called ferrous hydroxide. When this process is allowed to continue, the result is rust. Feedwater heaters are especially susceptible to this corrosive reaction due to their high temperatures.
How Do You Stop A Boiler From Corroding?
If you want to extend the life of your boiler, you need to know how to stop corrosion in heating systems. The main cause of corrosion in boilers is an excess of oxygen and/or CO2, which fuel the corrosion process. You should have your boiler properly installed and maintained to prevent the onset of corrosion. Keeping your boiler in good condition will help it last for 15 years or more. Always, always keep the system topped up with corrosion inhibitor, but it’s not always possible to stop corrosion.
It’s important to know how to prevent corrosion in boiler feedwater. Oxygen can attack metals in the boiler feedwater, which can cause corrosion failure of feedwater piping, economizers, and tubes. Iron oxide deposits can also contribute to corrosion in boilers, and these deposits can lead to performance problems and catastrophic failure. To stop corrosion, you should monitor the pH level of your boiler’s feedwater.
How Long Should A Radiator Last Before It Rusts?
When well maintained, a radiator can last decades. Consider these tips to make sure that your radiator lasts for decades. Regularly clean your radiator and use a soft sponge to blot off any water. Please don’t use harsh cleaning products as they may scratch the surface coating. Use a soft cloth to dry your radiator after cleaning.
Regularly flush your radiators to prevent rust and dirt from collecting. Dripping dirty water from your radiators can also damage your vehicle’s transmission due to overheating and damaging your heating system. By regularly flushing your radiators, you can also avoid problems with your radiator. It will prevent dirt and debris from clogging the radiators and causing leaks. If you notice rust-brown coolant from your radiator, it’s time to change it!
White vinegar and salt are effective rust-removal remedies. Lemon or lime juice contains citric acid, which helps remove rust. Apply this solution to the affected area and let it sit for two to three hours. Another quick and easy solution is to make a paste of baking soda and water. Allow it to dry, then scrub it off with a soft brush.
Can You Fix A Corroded Radiator?
If your radiator needs repair, you can clean it yourself using a mixture of white vinegar and water. Add a bit of lemon juice to mask the unpleasant smell. Use a microfibre cloth to wipe down the radiator after dipping it into the mixture. The most common cause of corrosion is sludge, a black mud-like substance that accumulates inside the radiator over time. It can lead to leaks and rusting.
The first sign that your radiator is corroding is a leak in one or more hoses. You can identify this leak by turning off the radiator and seeing the green liquid. Some leaks can happen inside the radiator. It can be a big problem since the coolant runs under high pressure from the radiator to the hot engine, creating pressure and overheating. The presence of green fluid in your radiator indicates a leak and can cause a corroded radiator.
Sometimes, a leaky radiator is easy to fix by yourself, but it’s often best to leave it to a professional. To begin a repair, turn off the heat and locate the bleed valve. A small round valve with a square opening typically sits on the top of the radiator. Unscrew this valve carefully. It will hiss, releasing trapped air. Close the valve after it stops hissing. You likely need to call a professional if you don’t hear the hissing sound or see the water.
Corrosion can cause many problems in heating systems, such as leaks, blockages, and loss of efficiency. It is important to inspect your heating system regularly for signs of corrosion and to have it serviced by a qualified professional if necessary.