What are the 14 causes of boiler tube rupture and their prevention measures

Fourteen causes of boiler tube rupture. Boiler tube rupture refers to the rupture of water-cooled wall tubes, convection tubes, and economizer tubes in the heat exchange surface of a boiler during operation, due to a combination of factors such as overheating, wear, and corrosion. This leads to high-temperature boiler water leakage and prevents the boiler from operating normally. Through years of theoretical accumulation and field practice, it has been found that boiler tube rupture is mainly caused by fourteen reasons.

1. Poor boiler tube feedwater quality, lack of water treatment, or incorrect water treatment methods, such as failure to perform blowdown treatment according to relevant regulations, causes scaling or corrosion on the inner wall of the boiler tubes. The main reason for this is that some boilers draw water from underground, which is high in hardness and has high sulfur and iron content. If the water treatment is not done properly, boiler tube rupture is very likely to occur, leading to forced shutdown for emergency repairs and causing a significant impact on production and daily life.

2. During the manufacturing, installation, and maintenance of boiler pipelines, stress concentration and decreased mechanical properties can occur at weld joints. These critical areas of stress concentration and mechanical degradation can lead to pipeline rupture, causing boiler failure and hindering the supply of production and domestic needs.

3. During boiler installation or maintenance, impurities may fall into the boiler tubes, causing blockages and impairing or completely disrupting water circulation.

4. Scale buildup on the inner walls of the boiler tubes can create bridging, hindering water circulation.

5. Low water levels during boiler operation can also lead to poor water circulation, causing localized overheating, deformation, and even rupture of the pipelines.

6. In oil, gas, or coal boilers, improper nozzle angle adjustment during design and installation can cause overheating in some boiler pipelines.

7. Incorrect start-up and shutdown operations, exposure of boiler tubes to cold air, and excessively rapid or frequent thermal expansion and contraction of the boiler tubes can generate harmful stress.

8. Damage to the flue and combustion chamber baffles causes short-circuiting of flue gas, resulting in localized heat concentration in the boiler tubes and ultimately, burnt-out tubes.

9. Corrosion-induced tube rupture and aging-related tube rupture generally occur in the economizer tubes of the tail-end heating surface. This is caused by acid corrosion due to excessively low exhaust gas or feedwater temperatures.

10. Excessively high local flue gas velocity occurs when the pitch of the boiler tubes and the distance between the tube banks and the furnace wall do not meet design requirements during installation and maintenance of the heating surface tubes. This creates localized flue gas corridors between tube banks or between tube banks and the furnace wall, or when some boiler tubes deviate from their designated positions, causing ash accumulation and bridging in the heating surface tubes. This leads to excessively high local flue gas velocities, increasing wear and overheating in those areas.

11. Due to careless construction, the furnace wall seals were not strictly sealed according to construction requirements, causing eddies at the leaks. This can lead to localized overheating or uneven heating of the pipelines. The leaks also increase the flue gas velocity downstream, damaging the tail-end heating surfaces.

12. High-temperature operation of boiler tubes is also a significant cause of boiler tube rupture. Overheating and exceeding temperature limits cause the mechanical properties of the boiler tubes to deteriorate due to excessive temperature. Under pressure, the tubes undergo plastic deformation, i.e., creep cracking, ultimately leading to rupture.

13. Environmental factors can also cause boiler tube rupture. These include frequent boiler start-ups and shutdowns, drastic load changes, improper flame centering, primary and secondary air scouring of water-cooled wall tubes, and rapid cooling during shutdown. All of these factors create potential hazards for boiler tube rupture.

14. Carbon dioxide or oxygen corrosion exists in the boiler heating system piping network or the steam condensate piping network. When oxygen and carbon dioxide are present simultaneously in the boiler return water system, the corrosion of the system piping steel becomes more severe. Carbon dioxide makes the water slightly acidic, damaging the protective film of the pipes. As the oxygen content increases, large or small ulcers appear on the carbon steel equipment and piping of the heating system, accelerating corrosion. The result is that the return water or condensate turns yellow, red, or even soy sauce-colored, has a high iron ion content, and exhibits perforation in the steel pipes. This is the common cause of corrosion, perforation, and leakage in steam and condensate pipes. This is also why some newly built boiler carbon steel pipes have a service life of only 4-5 years.

Six Measures to Prevent Boiler Tube Bursts

To reduce and eliminate boiler tube bursts and ensure the needs of production and daily life, the following six measures are implemented to prevent boiler tube bursts:

1. Strengthen the management of water treatment and water quality monitoring, increase deoxygenation and iron removal equipment, and change from single-stage softening to two-stage softening to ensure that boiler water meets national standards, ensuring the safe and economical operation of the boiler.

2. Make full use of the maintenance time after boiler shutdown. Have an authoritative institution, such as the Municipal Boiler Inspection Institute, conduct a comprehensive internal and external inspection of the boiler to promptly identify and address any problems, ensuring healthy boiler operation.

3. Strengthen operational management, organize reasonable combustion conditions and appropriate flame centering, prevent cold air from purging the boiler tubes, improve wear and corrosion prevention measures, and conduct proper blowdown.

4. After shutdown, promptly descale and clean the flue gas, and perform proper maintenance.

5. Appropriately increase the flue gas temperature (150-170 degrees Celsius is recommended), balancing safety and energy conservation, eliminating energy waste, and preventing the generation of condensate at the tail end.

6. Add a high-efficiency boiler corrosion and scale inhibitor, BF-30a, to prevent scale formation on the boiler's metal surface in high-hardness water.