Fire hazard and safety measures of the hottest wel

2022-08-17
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Fire hazard and safety measures of welding and cutting operation

1.1 overview

welding is a method of connecting metal parts. Use the heating, melting or pressurization at the junction of two metal parts, or both, to cause the bonding between metal atoms and molecules to obtain a permanent connection. In the Warring States period more than 2000 years ago, China used brazing to connect copper wares. The forging and welding method of iron has been recorded in Song Yingxing's "Tiangong Kaiwu" of the Ming Dynasty: "all iron properties are bonded section by section, coated with yellow mud on the interface, and people wave their mallets with fire, and the mud dross forms and goes away. Take its God as the medium, and after cementation, it is not cut with a burning red axe, and it will never be broken". It has steady and fast process performance, which fully shows that our people have invented welding technology long ago

welding technology is an important processing technology in modern industrial production. Compared with riveting, threaded connection and other metal connection methods, the large coal enterprises represented by Huawei began to strongly increase the long-term price in the first quarter, save metal materials, reduce labor intensity, improve production efficiency, and maintain good water tightness and air tightness. Therefore, it is widely used in the manufacture and repair of chemical industry, ships, vehicles, aircraft, bridges, boilers and other metal structures and machine parts. In the past 20 years, due to the emergence of many new welding technologies and processes, its application scope has been expanded day by day. The number of welders is also increasing, with more than 170000 in Shanghai alone, which has become an important technical force to rapidly improve China's industrial production technology

cutting is another production process operated by welders. It uses the high temperature generated by the mixed combustion of acetylene and other combustible gases with oxygen to melt the metal cutting place, and at the same time, uses air flow to blow away the molten metal, so as to achieve the purpose of cutting the metal. The production efficiency of gas cutting is much higher than that of mechanical cutting, and it is widely used to cut steel and other metal components. Compared with oxygen acetylene cutting, modern plasma cutting and other new processes have significantly improved the cutting quality, metal thickness and production efficiency

welding and cutting belong to open fire operation, which has the characteristics of high temperature, high pressure, flammability and explosion. They often deal with flammable and combustible substances and pressure vessels, so there is a greater risk of fire and explosion. Such accidents account for a large proportion of fire and explosion accidents in factories and enterprises, especially in the repair and construction of ships and the maintenance of chemical equipment. A little attention will cause major disasters. The fires of 10000 ton ships such as "Fenglei" and "Yixing", the explosion and sinking of "Daqing 53" oil tanker, and the fires of several large oil tanks in China were all caused in the process of welding and cutting. Such accidents are not only harmful to the life safety of welders, but also cause huge losses to production and national property. Therefore, it is of great significance to do a good job in the fire and explosion prevention of welding and cutting processes

for nearly a century, the basic methods of welding have been heating and pressurization. However, with the continuous development of science and technology, various welding methods emerge in endlessly

1.2 with the implementation of Internet technology and the maturing of social network ecology, fire risk and fire prevention and explosion prevention

<1. Gas welding, gas cutting

(1) gas welding, gas cutting equipment

gas welding is a fusion welding method that uses the flame of mixed combustion of combustible gas and oxygen to heat metal materials. The combustible gases commonly used in gas welding mainly include acetylene and propane, as well as hydrogen, natural gas, coal gas or liquefied petroleum gas

gas welding equipment and appliances include oxygen cylinders, acetylene cylinders, flashback preventers, welding torches, pressure reducers, rubber tubes, etc

gas cutting is the process of using the flame of mixed combustion of combustible gas and oxygen to heat the metal to the combustion point, and burning violently in the oxygen jet to separate the metal. "To achieve this goal.". The mixing of combustible gas and oxygen and the injection of oxygen are completed by cutting torch. The combustible gases used for gas cutting mainly include acetylene, propane and hydrogen

gas cutting equipment and appliances are the same as gas welding except for cutting torch

(II) explosion risk of gas welding and gas cutting

gas welding and gas cutting have great fire and explosion risks, mainly:

(1) acetylene, hydrogen, coal gas, natural gas and liquefied petroleum gas used in gas welding and gas cutting are flammable and explosive gases; Oxygen has strong combustion supporting property and extremely active chemical property; If you don't pay attention, it is easy to burn and cause explosion

(2) the equipment and appliances used in gas welding and gas cutting, such as acetylene generator, acetylene cylinder, liquefied gas tank and oxygen cylinder, are pressurized or high-pressure vessels, and the equipment and appliances themselves have great risk factors

(3) the flame temperature of gas welding and gas cutting is high, and molten metal sparks splash everywhere during operation. If splashed on the surrounding combustibles, it can cause smoldering and fire. Especially when gas cutting is carried out, the temperature is higher, the molten metal oxide is more, and the splash distance range is larger, which makes the risk of fire more prominent

(4) gas welding is widely used. Thin metal containers, such as gasoline drums, gasoline tanks, and various metal containers, cannot be repaired without gas welding. The explosion is often caused by the residual gasoline and flammable gas in these containers contacting the welding and cutting flames

(5) at the welding and cutting sites, many combustible, flammable and explosive substances and various pressurized containers and pipelines will be encountered. Therefore, among all welding and cutting processes, gas welding and gas cutting are the most dangerous, with the highest proportion of fire and explosion accidents

II. Arc welding, cutting

(I) principle of arc welding and fire risk

1. Principle of arc welding

arc is a strong gas discharge phenomenon between electrodes with a certain voltage or between electrodes and weldments

in general, because the molecules and atoms of the gas are neutral, the gas has no charged particles, so the gas cannot be charged, that is, it cannot transmit electricity. But under the specific condition that the electrons in the molecules or atoms in the gas get enough energy from the outside, the gas can also transmit electricity. Arc welding is based on this basic principle. When the contact between electrodes or between electrodes and weldments produces gas discharge, the electrodes and weldments are immediately separated, and a certain gap is maintained. The thermal energy of electricity promotes the gas to generate electricity and form a continuous and lasting arc. However, this effect of gas electricity transmission can only be formed at a relatively high temperature and a very small distance. If the heat energy is insufficient or the spacing is slightly larger, the ability of gas to transmit electricity will be lost. Even if a continuous and lasting gas discharge has been formed, the discharge will stop due to the influence of heat energy and the spacing between electrodes. The temperature of the arc center can reach ℃, which makes the metal electrode and the metal material of the weldment melt at the same time to form a weld

2. Types of arc welding and fire hazard

there are many types of arc welding, including manual arc welding, submerged arc automatic welding, submerged arc semi-automatic welding, and on this basis, electroslag welding, plasma welding, electron beam and carbon arc gouging are further used, but the basic principles are similar, all belong to the type of fusion welding. The fire risk of arc welding is different from that of gas welding and gas cutting. Flammable and explosive oxygen acetylene gas should be used in gas welding and gas cutting. Arc welding reduces the risk in this regard, but increases the risk factors of electrical fire; In addition, the flame temperature of arc welding is much higher than that of oxygen acetylene flame; The energy of heat conduction and heat diffusion of arc also exceeds that of oxygen acetylene flame; Especially the loop line (commonly known as ground wire) in arc welding is also a common cause of fire accidents. If it is not used properly, electric shock casualties will occur. Therefore, arc welding is also a special type of work that is prone to fire accidents in welding and cutting processes

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