Welding Introduction
Welding is a general term for various processes used to join metal parts by producing coalescence, called a weld, at a joint. This is usually done by applying heat and energy whilst bringing the pieces of metal together. This course will refer to the fire dangers and precautions of not only welding, but also cutting metals, which is similar to welding except that the metals are separated instead of joined.
As welding (and cutting) involves very high temperatures (up to 5500 degrees C), there is always the risk of fire, especially when combustible materials are around. These fires cause millions of dollars damage each year and the loss of life. Therefor it is important to recognize and understand the dangers and risks involved when welding, and to implement safe practices to reduce these risks.
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the work pieces and adding a filler material to form a pool of molten material (the weld pool) that cools to become a strong joint, with pressure sometimes used in conjunction with heat, or by itself, to produce the weld.
This is in contrast with soldering and brazing, which involve melting a lower-melting-point material between the work pieces to form a bond between them, without melting the work pieces.
Many different energy sources can be used for welding, including a gas flame, an electric arc, a laser, an electron beam, friction, and ultrasound. While often an industrial process, welding may be performed in many different environments, including in open air, under water, and in outer space. Welding is a hazardous undertaking and precautions are required to avoid burns, electric shock, vision damage, inhalation of poisonous gases and fumes, and exposure to intense ultraviolet radiation.
19th Century
Until the end of the 19th century, the only welding process was forge welding, which blacksmiths had used for centuries to join iron and steel by heating and hammering. Arc welding and oxyfuel welding were among the first processes to develop late in the century, and electric resistance welding followed soon after. Welding technology advanced quickly during the early 20th century as World War I and World War II drove the demand for reliable and inexpensive joining methods. Following the wars, several modern welding techniques were developed, including manual methods like SMAW, now one of the most popular welding methods, as well as semi-automatic and automatic processes such as GMAW, SAW, FCAW and ESW.
Developments continued with the invention of laser beam welding, electron beam welding, magnetic pulse welding (MPW), and friction stir welding in the latter half of the century. Today, the science continues to advance. Robot welding is commonplace in industrial settings, and researchers continue to develop new welding methods and gain greater understanding of weld quality.
To understand why welding/cutting pose such a dangerous fire hazard, this course will firstly discuss the most common welding practices. The extent of the danger will then be discussed. The ways in which welding/cutting operations cause fires is described, which then leads into a comprehensive discussion of precautions and safety practices that should be implemented when welding to reduce the risk of fire, or at least minimize the amount of damage caused. The conclusion will summarize both the fire dangers of welding, and the most important safety practices to reduce these dangers.
Background Cutting
Gas and arc welding equipment can also be used for cutting metals. In fact, oxyacetylene gas and arc cutting cause more welding environment fires than any other means. Oxyacetylene gas cutting is similar to oxyacetylene welding, except that the blowpipe is fitted with a cutting attachment and work is done at a greater pressure. The effect is quite dramatic as sparks of hot metal shower from the work. These sparks provide a potential ignition source for a fire.
Arc cutting is similar to arc welding, except that special electrodes are used and the molten metal is either oxidized or blown away. The electrodes are coated with an insulating material which does not conduct electricity, and hence they are non-consumable, unlike in arc welding where the electrodes are used up.
Welding Processes
Welding has many applications, both domestically and industrially. Some welded products include ships, aircraft, automobiles, electric and electronic parts, and in building and construction work. Although over 50 welding processes are used today, the most common ones are gas welding and arc welding.
Gas Welding
The most common gas welding process is oxyfuel welding, also known as oxyacetylene welding. It is one of the oldest and most versatile welding processes, but in recent years it has become less popular in industrial applications. It is still widely used for welding pipes and tubes, as well as repair work.
The equipment is relatively inexpensive and simple, generally employing the combustion of acetylene in oxygen to produce a welding flame temperature of about 3100 °C. The flame, since it is less concentrated than an electric arc, causes slower weld cooling, which can lead to greater residual stresses and weld distortion, though it eases the welding of high alloy steels. A similar process, generally called oxyfuel cutting, is used to cut metals.
Oxyacetylene welding (a form of gas welding) is the oldest type of welding and was developed at the beginning of the twentieth century. Oxygen and acetylene are fed into a torch and ignited to produce a burning gas with a temperature of around 3000 degrees C. The welder has good control of the weld, as they hold the oxyacetylene torch in one hand and a rod of filler metal in the other. The heat of the torch causes the filler metal to gradually fuse with the joint.