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Under prolonged high temperature, high pressure, and corrosive environments, boiler tubes are highly susceptible to burnout, bulging, or bursting. This not only causes production losses but can also pose serious safety risks. This article will analyze in detail the causes of boiler tube burnout and their solutions, focusing on overheating, corrosion, scale buildup, and wear.
The working principle of boiler tubes mainly involves two aspects: heat transfer and fluid flow.
In a boiler, fuel combustion generates a large amount of heat, which is transferred to the boiler tubes through the furnace. Boiler tubes are usually made of materials with good thermal conductivity, such as carbon steel and alloy steel. Heat is transferred from the furnace wall to the outer surface of the boiler tubes, and then gradually transferred to the fluid inside the tubes through thermal conduction.
The fluid inside the tubes is usually water or steam. As heat is transferred, the water is gradually heated and converted into steam. In this process, the fluid flows inside the boiler tubes, forming convective heat transfer. The fluid flow allows heat to be distributed more evenly throughout the tubes, improving heat exchange efficiency.
Boiler tube "burnout" is essentially a combined result of localized overheating and material failure. Industrial field statistics show that over 80% of tube ruptures are related to overheating.
If the temperature of the boiler tubes is too high during operation, exceeding the tube material's tolerance range, it is prone to burnout.
Overheating can be caused by various factors, such as improper boiler design, inadequate combustion control, and poor water circulation.
Short-term overheating:
Characteristics: Rapid temperature rise; rapid bulging and rupture of tube walls; plastic tearing of metal.
Common causes: Interruption of water circulation; uneven flame distribution in the furnace; severe scaling inside the tubes; uneven flow distribution.
Long-term overheating:
Characteristics: Prolonged high-temperature operation; metal creep; slow bulging of tube diameter; eventual tube rupture.
During long-term operation, boiler tubes are susceptible to erosion by corrosive substances in water, steam, and flue gas, leading to thinning of the tube walls, decreased strength, and ultimately, burnout.
Types and causes of corrosion:
Oxygen corrosion: Oxygen-containing feedwater.
Under-scale corrosion: Scale deposition.
Flue gas corrosion: SO₂, Cl⁻.
Alkali corrosion: Concentrated NaOH.
High-speed flow of water, steam, or flue gas within the boiler tubes causes erosion and wear on the tube walls. Over time, the tube walls gradually thin, even developing perforations, leading to burn-out.
This is most common in the following areas: elbows, header outlets, throttling zones, and reheater inlets.
The quality of boiler water directly affects the service life of boiler tubes. Improper water treatment causes impurities and hardness components in the water to form deposits (carbonate scale, sulfate scale, silicate scale, iron scale) on the tube walls, affecting heat transfer efficiency and even causing under-deposit corrosion.
|
Scale Thickness |
Tube Wall Temperature Rise |
|
0.5 mm |
20–30℃ |
|
1 mm |
Above 60℃ |
|
2 mm |
May cause tube rupture |
Generally, boiler tubes are prone to burn-out when heated above 650℃, but this depends on the material of the boiler tubes. This is because high temperatures can cause deformation or damage to the boiler tubes, affecting the safe operation of the boiler.
Generally, boiler tubes are designed to operate within a temperature range of 500℃ to 650℃. Within this range, boiler tubes maintain good performance and safety. However, when the temperature exceeds 650℃, boiler tubes are easily damaged.
High temperatures can cause changes in the boiler tube material, leading to decreased strength, deformation, and even cracking. Furthermore, prolonged exposure to high temperatures accelerates the aging process of boiler tubes, shortening their service life.
Common boiler tube material temperature ranges:
Carbon steel (20G / ASTM A106 Gr.B): ≤ 450℃
Low alloy steel (T11 / T22): 500–580℃
High alloy steel (T91 / T92): 600–650℃
Stainless steel: Higher temperatures are possible.
First, it is necessary to confirm the specific location and extent of the burnt section.
If the burn is small, it can be repaired with a pipe clamp. If the burn is severe, the damaged part needs to be replaced.
Damage extent and repair measures:
Minor Pitting: Grinding + Monitoring.
Local Thinning: Tube Repair.
Bulging/Deformation: Must Replace.
Burst/Perforation: Must Replace.
If you are waiting for a repairman but need to keep the boiler running, temporary emergency measures can be used.
For example, use welding rods and strapping to temporarily repair and seal the burnt area to ensure normal boiler operation.
For serious problems like burnt-out boiler tubes, it is best to have a professional repair it. Seek help from equipment repair companies or professional boiler repair organizations to ensure the long-term operation of the boiler.
Before repair, ensure proper safety procedures are followed, such as shutting off the flame, disconnecting power, and preventing burner ignition to ensure the safety of the repair process.
In addition to timely repairs, routine boiler maintenance is also necessary. This includes regularly cleaning boiler scale and promptly replacing easily worn parts such as the furnace and pipes. Strengthening daily maintenance can extend the boiler's service life and prevent malfunctions such as burn-out.
Field statistics show that localized overheating (especially caused by scaling) accounts for the highest proportion.
Not necessarily, but it is a serious warning sign and must be replaced as soon as possible.
Boiler tube failure is mainly caused by factors such as localized overheating, corrosion thinning, scale deposition, and erosion wear.
Among these, the most common cause is scale buildup or poor water circulation leading to poor heat dissipation, causing abnormal increases in tube wall temperature, ultimately resulting in bulging or bursting.
In summary, the main causes of boiler tube burn-out include overheating, corrosion, wear, and improper water treatment. To reduce the risk of burn-out, you need to address these aspects, strengthen equipment inspection and maintenance, and ensure the safe and stable operation of boiler tubes.
E-mail: sales@eastern-steels.com
