Fire prevention technology of the hottest electric

2022-07-29
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Fire prevention technology of electric welding site

electric welding is an indispensable process for metal cutting and bonding. The process of using pressure and heat energy to connect two separate metals together is called welding. There are many kinds of welding. At present, arc welding is the most widely used. Arc welding is to take the electrode as one electrode of the circuit and the weldment as the other electrode, generate high heat by using the principle of contact resistance, and form an arc to melt the metal for welding. Arc welding is widely used in production and construction. It belongs to open fire operation, and it is easy to cause fire and explosion accidents when dealing with flammable, combustible and explosive substances and pressure vessels. Fires caused by illegal electric welding are not uncommon, among which the catastrophic fire accident caused by illegal electric welding sparks in Luoyang Dongdu commercial building in Henan Province in 2000 was the most painful, resulting in 309 deaths. Reflect on the lessons of these accidents, and put forward relevant preventive measures for reference in combination with the characteristics of flammability, high temperature and high pressure in our chemical industry zone

I. fire risk at the welding site

there is both electricity and open fire at the welding site. If the mind is paralyzed, the operation is improper, the system is not strict, and the safety measures are not implemented, it is very easy to cause a fire. Arc welding uses the arc heat energy to achieve the purpose of fusion welding. The arc energy generated during starting operation is large and continuous. For example, the arc during open arc welding can reach more than 4200 ℃, so the fire hazard of high temperature can be imagined, and the required electrical equipment and lines also contain great fire hazard. The following focuses on the analysis of the causes of fire hazard at the welding site from the perspective of causing welding fire, but the transformation of ideas and management modes can not be ignored. The automatic calculation of Zui large force, upper and lower yield strength and hysteresis at the end of the fire hazard test at the welding site

(I) ignition and detonation of welding sparks

the molten metal in the welding process causes metal sparks to splash due to the rapid cold and hot air exchange, chemical reaction and external force. These solid metal sparks have high heat energy and the temperature is above 1000 ℃. They have distinctive characteristics: first, they have a long cooling time. In some welding sites, after the work is completed, the surface welding sparks have been extinguished, The surface temperature has not fallen below the ignition point of the combustible. If you are careless, it will cause combustion. Second, there is a certain self weight. Under the action of self gravity, the metal particles dropped by welding will pass through the gaps and holes of vertical pipes and buildings, causing foreign fires. Third, irregular spatter and spark spatter are random, especially for high-altitude welding, which is greatly affected by wind and other factors, and the spatter range is wide. If the residue is not completely removed in time, it will leave hidden dangers. All these have increased the fire load on the welding site. If the prevention is not in place, it will cause combustion when encountering combustibles. If there is combustible gas, it is very easy to cause explosion

(II) ignition of welding circuit fault

the energy of arc welding depends on wires. Improper selection, aging insulation, wrong connection, etc. will burn the wires or cause fire

1. Wire overload. The welding circuit is a large capacity power supply line with a current of tens to hundreds of amperes. In this way, higher requirements are put forward for the connection and type selection of conductors. Generally, multi stranded copper cables are used. Sometimes, if the welding personnel can not find the required cables or do not understand them, they will use ordinary insulated conductors with small cross-sectional area to temporarily replace them. This will cause the welding conductors to overload and heat. The light ones will burn the conductors themselves, and the heavy ones will ignite the combustibles around the conductors and cause electric shock accidents

2. Remote discharge of welding circuit current. The welding tongs and the grounding wire form a loop through the weldment. During welding, the fused parts have a certain voltage value. If the welded parts are metal or pipe and there is a gap, strong discharge sparks will be generated at the middle gap of the welded parts, resulting in unexpected fire. In 1978, when a textile factory in Shanghai was rebuilding its warehouse, when welding and fixing the steel bars on the second floor, a gap occurred. The mechanical universal experimental machine realized electric spark by using the lever principle, so that a large number of cotton bales were burned in the warehouse

3. Welding cable burns. The welding cable has a certain service life. If it is not replaced in time, the insulation layer will be aged, and the performance of insulation, including researchers and engineers, will be reduced. Moreover, due to thermal mechanical damage or material corrosion of the welding cable, part of the insulation layer will lose its original insulation capacity. In this way, when the welding is carried out, the crossed positive and negative wires will generate leakage or short circuit, resulting in cable combustion. In addition, in shipbuilding and construction industries, high-altitude electric welding is mostly required. When the welding point is higher than the lower cable, the falling welding arc will also burn the cable

(III) heat conduction ignition

the objects of welding are mostly metals with good thermal conductivity, which is very easy to transfer the heat generated by the welding point to several meters away. If there are a large number of combustibles in the operation area, the transferred heat will accumulate for a long time. Once the fire energy exceeds the lowest point of these combustibles, it will cause foreign combustion. This kind of fire is often seen in the welding of cold storage, ventilation and other pipes

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