Thread Content
Basic knowledge of boiler and pressure vessel safety ① How are boilers classified? There are 5 ways to classify boilers: (1) Divided according to use: Power station boilers, industrial boilers, domestic boilers. (2) According to the pressure, they are divided into: low-pressure boilers, medium-pressure boilers, high-pressure boilers, subcritical boilers, and supercritical boilers. (3) Divided according to water and fire processes: Water tube boilers and shell boilers. (4) According to fuel, they are divided into: coal-fired boilers, oil-fired boilers and gas-fired boilers. (5) According to the combustion method, it is divided into: layer-fired boiler and chamber-fired boiler. ②Why are the accident frequency of boilers and pressure vessels relatively high? The accident frequency of boilers and pressure vessels is relatively high, which is related to the characteristics of the equipment itself: (1) The structures of boilers and pressure vessels are generally relatively simple, but their stress conditions are relatively complex. There are both primary stress and secondary stress, as well as peak values, temperature stress, residual stress, etc. In particular, stress concentration is likely to occur at openings and geometric mutations. In addition, it is also subject to cyclic stress, causing low-cycle fatigue. (2) The working and usage conditions are relatively complex. The boiler is directly heated by the flame, the temperature changes greatly, the heating is uneven and local overheating may occur. The working conditions of pressure vessels are variable (from high temperature to cryogenic temperature), and the pressure is also variable. Therefore, any tiny defects left in the manufacturing process may, under appropriate conditions, rapidly expand and cause accidents. (3) Overload operation is prone to occur. Boilers are often overloaded due to operator errors and instrument failures, while pressure vessels are more susceptible to sudden changes in chemical reactions and instrument failures, causing overloading. Once the equipment is overloaded, if the safety device is faulty or ineffective, it may quickly lead to an accident. (4) Susceptible to corrosion by working medium. During the production process, due to the corrosion of the working medium, the wall thickness changes from thick to thin and the material deforms, and the pressure accelerates this corrosion, such as intergranular corrosion and stress corrosion of pressure vessels. ③How to classify accidents of boilers and pressure vessels? What are the hazards of accidents? According to the "Measures for Reporting Accidents of Boilers and Pressure Vessels", accidents of boilers and pressure vessels can be divided into 3 categories according to the degree of equipment loss: (1) Explosion accidents. An accident in which boilers and pressure vessels rupture during use, causing the pressure to instantly drop to atmospheric pressure. When an accident occurs, the process in which the huge energy contained in the equipment is released instantly is called an explosion. Explosion accidents will destroy equipment and buildings, cause casualties, and have serious consequences. (2) Major accidents. Accidents in which the pressure-bearing parts or other main components of boilers and pressure vessels are seriously damaged and forced to stop operation and require overhaul are considered major accidents. The important difference from explosion accidents is that: The pressure does not drop to atmospheric pressure instantly, but there is a pressure relief process. (3) General accidents. An accident in which parts are damaged but not seriously, and generally do not require stopping operation for repairs. The main difference from a major accident is that: Whether the pressure components or other major components are damaged and require immediate overhaul. The hazards caused by accidents of boilers and pressure vessels are more serious: (1) When explosion accidents occur in boilers and pressure vessels, not only the accident equipment is destroyed, but also surrounding equipment, buildings and people are affected. The fragments directly produced by the explosion can fly hundreds of meters away and generate huge shock waves, which are extremely destructive and lethal. (2) After major accidents of boilers and pressure vessels, the spillage of working medium may cause a large number of casualties. For example, after a boiler or sub-cylinder explodes, the high-temperature saturated water immediately evaporates into high-temperature steam, causing severe burns and death. Another example is the large spillage of toxic substances in pressure vessels (liquid chlorine, liquid ammonia, etc.) that turn into poisonous gas and spread rapidly, which can cause serious accidents in which a large number of people and animals are poisoned. A large amount of leakage of flammable substances can also cause major fires and secondary explosion accidents, with very serious consequences. ④What are the common causes of boiler and pressure vessel accidents? There are many causes of boiler and pressure vessel accidents. The common causes are: (1) Defects in the equipment itself. Equipment defects can be formed during the design and manufacturing process, such as unreasonable structure, substandard materials, poor welding quality, and insufficient strength of pressure components. It can also be gradually formed due to fatigue and corrosion during operation. (2) The safety accessories are incomplete or malfunctioning, or the safety accessories are not installed, or the installation is unreasonable, but more often than not, the safety accessories are inaccurate or ineffective due to long-term operation and disrepair. (3) Poor management or abnormal operation. Such as illegal operations, misoperation, poor boiler water quality management, lack of regular inspection and maintenance systems, etc. ⑤What are the three major safety accessories of the boiler? What are the functions of each? The three major safety accessories of the boiler are the safety valve, pressure gauge and water level gauge. The function of the safety valve is that when the steam pressure in the boiler exceeds the allowable value, the safety valve automatically opens and exhausts steam to the outside. When the pressure drops to the specified value, it automatically shuts down to prevent the boiler from exploding due to overpressure. The pressure gauge is an instrument used to measure the steam pressure in the boiler. The boiler uses it to monitor changes in the steam pressure in the boiler. The water level gauge is a direct-reading instrument used to reflect the water level in the drum. Boiler workers use it to monitor changes in the water level in the drum. ⑥What are the common accidents in boiler operation? (1) The boiler is short of water. A serious lack of water in the boiler will cause deformation and damage of the pressure components, and even an explosion of the furnace tube. If not handled properly, a boiler explosion accident may occur. When it is found that the boiler is short of water, water inflow should be strictly prohibited and emergency shutdown measures should be taken. Most of the causes of boiler water shortage accidents are related to the operator's laxity, paralysis and misoperation, or the water level meter is blocked due to no flushing measures. (2) Soda and water are shared. The characteristics of soda and water are:: The water level on the water level meter fluctuates violently, the pot water bubbles, the steam contains a large amount of water, the steam temperature drops, and in severe cases, water shock occurs in the pipe. The main reasons for this situation are: poor water quality, too high salt content or too rapid increase in boiler load. When it is found that soda and water are evaporating together, water quality treatment must be strengthened and continuous sewage discharge must be increased. (3) Boiler overpressure. The overpressure operation of the boiler may cause deformation of components and damage to joints; in severe cases, it may cause explosion accidents. The main reason for boiler overpressure is that boilers blindly increase working pressure or leave their jobs without authorization. Sometimes, boiler overpressure can also be caused by simultaneous failure of the pressure gauge and safety valve. Therefore, it is necessary to strengthen the inspection of the boiler's job responsibility system and safety accessories. (4) Furnace tube explosion. When the furnace tube explodes, there will be obvious blasting and steam spraying sounds, and at the same time, the water level and steam pressure will drop significantly. When this situation is discovered, emergency shutdown measures must be taken. The general reason for this situation is: poor water quality causes scaling or corrosion of the furnace tube; water shortage and tube explosion may also cause each other. In addition, pipe burst accidents may occur due to design defects, insufficient material strength and poor welding quality. ⑦After an accident occurs with a boiler or pressure vessel, how to handle the emergency? (1) Organize rescue. The so-called rescue should include two aspects:: First, rescue the injured immediately ； The second is to take various measures to prevent the accident from spreading, such as cutting off power and fire sources, emergency evacuation of personnel, and preventing continuous explosions. (2) Protect the scene. Unless it is possible to expand the accident, or there are injured people who need emergency rescue or serious traffic congestion, which affects important normal activities and must be cleaned up in time, no changes to the scene (including saving and marking scattered parts) are allowed as the main basis for finding out the accident. (3) Accident investigation. The investigation of accidents provides sufficient scientific basis for analyzing accidents to find out the causes of accidents. An accident investigation team should be established as soon as possible after the on-site investigation. The focus is to investigate the damage to the equipment itself, especially the fracture of the explosive body, because it is an important basis for judging the accident. In addition, the condition of safety accessories must be collected and assessed. It is necessary to consult relevant technical information and conduct technical appraisal of the materials. Only after mastering a large amount of first-hand information can we draw realistic conclusions. (4) Accident handling. Units that experience major accidents or casualties involving boilers and pressure vessels should fill in a "Boiler and Pressure Vessel Accident Report" and submit it to the relevant departments after finding out the cause. The "Report" should report in detail the basic situation of the accident, the cause of the accident, and the economic losses, and propose responsibility analysis and treatment opinions for those responsible, as well as measures to prevent recurrence of the accident. During the accident handling process, we must adhere to the principle of "four no-misses".