During long-term operation, boilers are prone to corrosion due to factors such as water quality, operating parameters, and equipment materials. Corrosion can damage boiler components, shorten their service life, and even lead to safety incidents. Many people are unaware of the different types of boiler corrosion or how to prevent them. Below is a detailed explanation—a must-read.
Common Type 1: Oxygen Corrosion—the most common type of corrosion. Oxygen corrosion occurs when oxygen in the water reacts with the boiler’s metal components, causing the metal to corrode. It primarily affects the boiler’s heat transfer surfaces, drum, and piping, manifesting as pitting and perforations on the metal surface. The main cause of oxygen corrosion is excessive dissolved oxygen in the water; this issue is particularly severe in high-temperature, high-pressure boilers.
Prevention Methods: Implement effective deoxygenation treatments, such as thermal or chemical deoxygenation, to reduce the dissolved oxygen content in the water and ensure it meets standards; conduct regular water quality tests and adjust the dosage of deoxygenation agents promptly; perform water softening treatment to reduce scale formation and prevent scale from exacerbating oxygen corrosion.
Common Type 2: Under-scale Corrosion: Corrosion caused by scale. When scale adheres to heat transfer surfaces, it creates enclosed spaces. The water beneath the scale reacts with metal components due to oxygen deprivation and deteriorating water quality, leading to under-scale corrosion. This type of corrosion is highly concealed, poses greater risks, and can easily result in perforations of heat transfer surfaces or tube bursts.
Prevention Methods: Perform regular descaling to promptly remove scale from heat transfer surfaces and prevent scale buildup; implement effective water treatment using softened water to reduce scale formation; Conduct regular inspections of the heat transfer surfaces; address scale buildup promptly upon discovery to prevent the formation of enclosed spaces.
Common Type 3: Acidic corrosion, caused by excessively acidic water. If the pH of the boiler water is too low (below 7), it can lead to acidic corrosion of metal components, manifested as uniform corrosion and thinning of the metal surface; in severe cases, this can result in component failure. The primary causes of acidic corrosion are improper water treatment or excessively acidic make-up water.
Prevention methods: Regularly test the water’s pH to ensure it remains within the specified range (pH 10–12 for steam and hot water boilers); if the pH is too low, promptly add alkaline substances such as sodium hydroxide solution to adjust the pH; properly treat makeup water to prevent acidic water from entering the boiler.
Common Type 4: Stress Corrosion, triggered by a combination of metal stress and a corrosive environment. Boiler components undergo certain stresses during manufacturing and installation; when exposed to a corrosive environment (such as high pressure, high temperature, or substandard water quality), stress corrosion can occur, leading to component cracking. This type of corrosion is extremely hazardous and can easily trigger sudden accidents.
Prevention Methods: Perform stress relief treatment during boiler manufacturing and installation; During operation, control boiler pressure and temperature to avoid excessive parameter fluctuations; implement proper water treatment to prevent the formation of corrosive environments; and conduct regular inspections of boiler components, repairing or replacing them promptly upon detection of cracks.
Note: The key to preventing boiler corrosion lies in proper water treatment, regular inspections, and timely maintenance. Only by preventing the formation of corrosive environments can corrosion be effectively reduced, the boiler’s service life extended, and safe operation ensured.
