Boiler tube bursting refers to the combined effects of overheating, wear, and corrosion on the water-cooled wall tubes, convection tubes, and economizer tubes in the heat exchange surface of a boiler during operation, resulting in pipeline rupture, high-temperature boiler water leakage, and the inability of the boiler to operate normally. Through years of theoretical accumulation and on-site practice, it has been found that boiler pipeline bursts are mainly caused by fourteen reasons.
The first reason
The quality of boiler feedwater is poor, there is no water treatment or the water treatment method is incorrect, and the sewage treatment is not carried out according to relevant regulations, resulting in scaling or corrosion of the inner wall of the pipeline. The main reason for this situation is that some boiler water is taken from underground, with a hardness of up to 5mmol/L, belonging to high hardness water, and high sulfur and iron content. Once the water treatment is improper, it is easy to cause pipe bursting and forced to shut down for repair, which has a great impact on production and life.
The second reason
During the manufacturing, installation, and maintenance process of boiler pipelines, stress concentration and mechanical performance degradation may occur at the welding joints. In these critical areas where stress concentration and mechanical degradation occur, pipeline rupture may occur, which can also cause boiler failures and make it difficult to supply production and daily needs.
The third reason
Impurities fall into the pipes during installation or maintenance of the boiler, causing blockages in the pipes and resulting in poor water circulation or complete destruction.
The fourth reason
The scale on the inner wall of the pipe falls off, creating a “bridge” that puts the water circulation in a poor state.
The fifth reason
If the water level of the boiler is too low during operation, it will also cause poor water circulation, which will cause the local temperature of the pipeline to be too high and deform until it bursts.
The sixth reason
During the design and installation of oil boilers, gas boilers, or coal boilers, some boiler pipelines may overheat due to incorrect adjustment of the nozzle angle.
The seventh reason
Incorrect ignition and shutdown operations, causing the furnace tubes to be blown by cold air, rapid or frequent thermal expansion and contraction of the tubes, resulting in harmful stress.
The eighth reason
The smoke duct and combustion chamber partition wall are damaged, causing a short circuit in the smoke and resulting in local heat concentration in the furnace tube, which burns out the furnace tube.
The ninth reason
Corrosion explosion and equipment aging explosion. It usually occurs in the economizer tube of the tail heating surface, due to acidic corrosion caused by low exhaust gas temperature or low feedwater temperature.
The tenth reason
The local smoke velocity is too fast. During the installation and maintenance of the heating surface pipes, the pitch of the heating surface pipes and the distance between the heating surface pipes and the furnace wall do not meet the design requirements. Local smoke corridors are formed between the pipe rows or between the pipe rows and the furnace wall, or some pipes are out of line, causing ash accumulation and bridging of the heating surface pipes, resulting in high local smoke velocity and increasing the wear and overheating of the pipes in that area.
The eleventh reason:
Due to careless construction, the sealing of the furnace wall was not strictly sealed according to the construction requirements, resulting in the formation of vortices at the leakage point. This situation can also cause local overheating of the pipeline or uneven heating, and the leakage also increases the flow velocity of the flue gas behind, endangering the heating surface at the rear.
The twelfth reason:
High temperature operation of pipes is also an important cause of boiler pipe bursting. Overheating and overheating pipe bursting are due to the mechanical properties of pipes decreasing under overheating conditions, and pipes undergoing plastic deformation, creep cracks, and even pipe bursting under pressure.
The thirteenth reason:
The influence of the operating environment can also cause the rupture of furnace tubes, such as frequent start-up and shutdown of boilers, drastic changes in load, improper adjustment of flame center, flushing of water-cooled wall tubes by primary and secondary air, and the impact of rapid cooling during shutdown, all of which leave hidden dangers for boiler tube rupture.
The fourteenth reason:
There is carbon dioxide corrosion or oxygen corrosion in the boiler heating system pipe network or steam condensate pipe network. When both oxygen and carbon dioxide are present in the boiler return water system, the corrosion of the system pipe network steel becomes more severe. Carbon dioxide makes the water slightly acidic and damages the pipeline protective film. With the increase of oxygen content, the carbon steel equipment and pipe network of the heating system will appear in a large or small ulcer state, accelerating the occurrence of corrosion. The result is that the color of the return water or condensate water turns yellow, red, and even presents a soy sauce color, high iron ion content, and steel pipe perforation. The common causes of corrosion, perforation, and leakage in steam and condensate pipelines are this. This is also the reason why the service life of some newly built boiler carbon steel pipelines is only 4-5 years, which means that the condensate water pipeline needs to be replaced every 4-5 years.
Excessive iron content in boiler return water not only causes the phenomenon of “red water” in boiler water, but also leads to corrosion under iron oxide scale. Moreover, it can also lead to the rapid formation of phosphate scale in the boiler. The thermal conductivity of iron oxide scale is poor, and the heat transfer efficiency of the iron oxide scale layer is significantly different from that of the furnace tube, seriously hindering heat transfer and causing local high temperatures on the heat transfer surface, resulting in a decrease in metal strength and endangering the safety of the boiler. This can cause deformation of the furnace tube and lead to tube bursting.
