Causes of boiler tube bursts and preventive measures

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Fourteen reasons for boiler tube failures: Boiler tube failure occurs when, during operation, the water wall tubes, convection tubes, and economizer tubes in the heat exchange surfaces of a boiler burst as a result of various factors such as overheating, wear, and corrosion. This leads to the leakage of high-temperature boiler water, preventing the boiler from functioning properly. Through years of theoretical research and on-site experience, it has been found that pipeline ruptures in boilers are mainly caused by fourteen different reasons.   The first reason is poor quality of boiler feed water, lack of water treatment or incorrect treatment methods, as well as failure to carry out proper sludge removal in accordance with relevant regulations. This leads to scaling or corrosion on the inner walls of the pipes. The main cause of this issue is that some of the water used in boilers comes from underground sources, with a hardness level as high as 5 mmol/L, meaning it is high-hardness water. It also contains high levels of sulfur and iron; improper water treatment can easily result in pipe explosions, forcing the shutdown of the boiler for repairs, which has a significant impact on production and daily activities. The second reason: During the manufacturing, installation, and maintenance of boiler pipelines, stress concentration and a decline in mechanical properties occur at the welds. Pipeline ruptures can happen at these areas where stress concentration and mechanical weakness exist, which in turn causes problems with the boiler and makes it difficult to meet the needs of production and daily life. Third reason: During installation or maintenance of the boiler, impurities fall into the tubes, causing blockages within them, which leads to poor water circulation or even a complete disruption of it. Fourth reason: Scale on the pipes detaches from the inner wall, forming \"bridges\" that disrupt the water circulation. Fifth reason: If the water level in the boiler is too low during operation, poor water circulation will occur. In such a situation, the temperature in certain sections of the pipes can become excessively high, causing them to deform or even burst. Sixth reason: With oil boilers, gas boilers, or coal boilers, improper adjustment of the nozzle angle during design and installation can also lead to overheating in some of the boiler pipelines. Seventh reason: Incorrect operations for starting up or shutting down the furnace, exposure of the furnace tubes to cold air, and rapid or frequent thermal expansion and contraction of the tubes, which generate harmful stresses. Eighth reason: Damage to the flue ducts and fire separation walls in the combustion chamber causes smoke to take a short circuit, leading to concentrated heat on certain sections of the furnace tubes and resulting in their damage. Ninth reason: corrosion-induced tube failure and equipment aging-induced tube failure. It generally occurs in the economizer tubes located on the heated surfaces at the tail end, due to acidic corrosion caused by excessively low flue gas temperatures or low feedwater temperatures. Tenth reason: The local flue gas velocity is excessively high. During the installation and maintenance of heating surface tubes, the spacing between the tubes as well as the distance between the tube arrays and the furnace wall do not meet the design requirements. This results in the formation of local flue gas corridors between or beside the tube arrays, or causes some tubes to become misaligned, leading to ash accumulation and bridging on the heating surface tubes. Consequently, the local flue gas velocity becomes too high, thereby increasing wear and overheating of the tubes in that area. Eleventh reason: Due to careless construction, the seals on the furnace walls were not properly sealed in accordance with the required standards, which led to the formation of vortices at the leakage points. This can result in localized overheating of the pipelines or uneven heating. Additionally, the air leakage increases the flow velocity of the smoke gases downstream, posing a threat to the heating surfaces at the rear of the furnace. Twelfth reason: The operation of pipes at high temperatures is also a significant cause of boiler tube failures. Tube failure due to overheating occurs because the mechanical properties of the pipes decline when they are exposed to excessive temperatures; under pressure, the pipes undergo plastic deformation, resulting in creep cracks that ultimately lead to tube failure. Thirteenth reason: The operating environment can also cause the furnace tubes to crack. Factors such as frequent start-up and shutdown of the boiler, sharp changes in load, improper adjustment of the flame center, the scouring of the water-cooled wall tubes by primary and secondary air, and the effects of rapid cooling during shutdown all pose risks of tube failure in the boiler. Fourteenth reason: Carbon dioxide corrosion or oxygen corrosion occurs in the piping networks of the boiler heating system, or in the steam condensation piping networks. When both oxygen and carbon dioxide are present in the boiler return water system, it accelerates the corrosion of the steel components in those piping networks. Carbon dioxide renders the water slightly acidic, thereby destroying the protective layer on the pipes; as the oxygen content increases, carbon steel equipment and piping in the heating system develop ulcers of varying sizes, further accelerating corrosion. As a result, the return water or condensation water takes on a yellow, red, or even soy sauce-colored appearance, the iron ion concentration rises, and the steel pipes may develop holes. This is the reason for the common corrosion, perforation, and leakage in steam pipes and condensate pipes. This is also why the service life of carbon steel pipes in some newly installed boilers is only 4–5 years, meaning that the condensate pipelines need to be replaced every 4–5 years. Excessive iron content in the boiler return water not only causes the \"red water\" phenomenon in the boiler water but also leads to corrosion beneath the iron oxide scale. It also leads to the rapid formation of phosphate salt scale in the boiler. Iron oxide scale has very poor thermal conductivity, and the heat transfer efficiency of this scale layer is significantly different from that of the boiler tubes, which severely hinders heat transfer. This results in excessively high temperatures in certain areas of the heat transfer surfaces, leading to a decrease in the strength of the metal and posing a threat to the safety of the boiler. It can also cause the boiler tubes to deform, resulting in tube rupture. Seven measures to prevent boiler tube explosions: To reduce and eliminate tube explosions and meet the needs of production and daily life, the seven specific measures for preventing boiler tube explosions are as follows: The first measure is to strengthen the management of water treatment and water quality monitoring; additional deoxygenation and iron removal equipment has been installed, and the softening process has been changed from primary to secondary softening, thereby ensuring that the water used in the boiler meets national standards and facilitating the safe and efficient operation of the boiler. Second measure: Make full use of the downtime for maintenance. Invite authoritative agencies such as the municipal boiler inspection office to conduct a comprehensive internal and external inspection of the boiler, identify problems promptly and address them, so as to ensure its proper operation. Third measure: Strengthen operation management, optimize combustion by establishing proper combustion conditions and an appropriate flame center, prevent cold air from flowing through the furnace tubes, improve measures to avoid wear and corrosion, and carry out proper slag removal. Fourth measure: Remove scale promptly and clean the smoke tubes after shutting down the furnace, and carry out proper maintenance. Fifth measure: Appropriately increase the flue gas temperature to prevent the formation of condensation water at the tail end. Sixth measure: Add the efficient boiler anti-corrosion and scale-inhibition agent BF-30a. BF-30a provides dual protection by keeping the metal of the boiler in a passivated state and suppressing the cathodic reactions that occur during metal corrosion, thereby effectively preventing oxygen-induced corrosion of the metal both during operation and when the boiler is shut down ； At the same time, due to its strong chelating ability, BF-30a forms stable water-soluble chelates with the hardness ions in boiler water once added to it, thereby increasing the solubility of these hardness ions in water. This prevents the formation of scale, and it also has the effect of slowly dissolving existing scale ； Due to its strong lattice distortion and dispersion effects, BF-30a causes calcium carbonate crystals to break apart during growth, resulting in small crystals with irregular shapes. The dispersant adheres to the surfaces of these small crystals as well as the metal surface, forming a double layer. Under the influence of electrostatic forces, these small crystals repel each other as well as the boiler metal surface, thereby preventing the formation of scale on the boiler metal surface in water with high hardness. Seventh measure: Addressing the fourteenth cause of tube failure, namely the situation in which the condensate return pipeline network of steam boilers experiences excessive iron ions due to oxygen corrosion and carbon dioxide corrosion, which leads to oxidation-induced scale formation in the boiler. This oxidation-scale also results in the rapid formation of phosphate scale within the boiler. Oxidation scale has very poor thermal conductivity, and the heat transfer efficiency of this scale layer is significantly different from that of the boiler tubes, thereby severely hindering heat transfer. This can cause localized overheating of the heat transfer surfaces, leading to a decrease in metal strength and posing a threat to the safety of the boiler; it can also cause the boiler tubes to deform and result in tube failure. In the condensate recovery system of boiler steam systems, the BF-31T condensate system protection technology is commonly used; the BF-31T condensate system protector, a patented product from Beijing University of Chemical Technology, is applied to prevent corrosion. This protector is a product that has been widely used in the market. Its main components include film-forming amines and neutralizing amines. The neutralizing amines in BF-31T have an alkaline nature, allowing them to neutralize carbonic acid present in the steam condensate, while also providing a basis for monitoring the concentration of chemicals in the water in real time. The BF-31T condensate system protector won the **Second Prize for Invention in 2007. BF-31T is a protective agent for condensate water systems. When added to water, it forms a monomolecular layer on the metal surface, creating a protective film with adsorptive and hydrophobic properties. The molecular gaps in this film are smaller than those of CO2 and O2, which prevents oxygen corrosion and weak carbonic acid corrosion in the system. This ensures that the iron ion concentration in the steam condensate meets the requirements specified in the national standard GB1576-2001 \"Water Quality for Industrial Boilers\", while also protecting the equipment and pipelines in the boiler steam system and condensate recovery system from corrosion, perforation, and leakage, thus addressing both the symptoms and root causes of the problem. Five requirements for the safety technical management and supervision to prevent boiler tube explosions: The first requirement is to register and keep records of pressure vessels, and to conduct thorough inspections of the water wall tubes, convection tubes, and economizer tubes. It is essential to keep track of the health status of equipment in a timely manner, to develop practical solutions for any potential safety hazards, and to nip accidents in the bud. The second requirement is to strengthen quality management throughout the entire process of major and medium-scale repairs, establish and improve a three-level management framework, strictly implement a three-level inspection system, and adopt a veto system. It will not be accepted if the requirements are not met. Third requirement: Regular inspection of the boiler; all defects identified during the inspection have been addressed. Fourth requirement: Strengthen water quality monitoring and maintenance after shutdown to reduce the scaling rate. Fifth requirement: Strengthen metal surveillance. During major, medium, and minor repairs as well as shutdown inspections, boiler tube failures should be checked in accordance with the standard inspection procedures. The main methods of inspection are visual inspection and tactile examination; any issues detected must be recorded and addressed promptly. Additionally, flaw detection tests should be carried out, and supervision of welds needs to be enhanced. Boiler safety is no trivial matter. The safe operation of boilers is crucial for both daily life and industrial production. It is essential to implement effective preventive measures and inspection procedures, eliminate potential hazards, and prevent boiler explosions, so that safe production in enterprises can go hand in hand with the safe operation of boilers