FERROUS PIPE-MAKING PROCESSES
Iron-Making
The making of steel for ferritic piping begins with the smelting of iron ore found in deposits in the crust of the earth throughout the world in forms such as hematite and magnetite. In preparation for the smelting process, the iron ore may be treated by any of several methods to convert it into a suitable form for introduction into the blast furnaces. One method is sintering, which converts ores into a porous mass called clinkers. Another is smelting, which is performed in a blast furnace. The process involves the chemical reaction of iron ore with limestone, coke, and air under heat, reducing the iron ore to iron. The ‘‘pig’’ iron obtained from the blast furnace is used as the basic component in the steel-making process.
Steel-Making
Steel for piping can be produced in several ways (Fig. A5.1), depending on the facilities available and the desired characteristic of the steel.Generally, steel requires the removal of carbon from the pig iron to a degree required by the carbon steel properties desired. Alloy steel also requires the addition of alloying elements such as chromium, nickel, manganese, and molybdenum to provide the special properties
associated with the alloying element.
Bessemer Converter. The Bessemer method of making steel (due to Sir Henry Bessemer in 1856) consisted of blowing a current of cold air through the molten pig iron, thereby using the oxygen in the air to burn carbon and other impurities from the melt. After burning out the carbon in the pig iron, the exact amount of carbon required for the steel is reintroduced into the heat.
Basic Oxygen Process. The basic oxygen process (BOP) is essentially the same as the Bessemer process except that it uses pure oxygen (instead of air) together with burned lime converted from limestone. This process burns out the impurities more quickly and completely and provides for more precise control of the steel chemistry.
Open-Hearth Furnace. The open-hearth furnace is used to produce much of the steel in the United States; however, it is being superseded by the basic oxygen process. Its significant advantage is the ability to use scrap steel as well as pig iron as ferrous stock in producing steel. The open-hearth furnace is a large rectangular brick floor, or hearth, completely covered with a brick structure through which the
charge of ferrous stock and limestone is introduced. It is fueled with coke gas, oil, or tar introduced through a burner playing a flame across the hearth while the products of combustion escape through the furnace wall away from the burner. An advantage of the open-hearth process is that testing for carbon content during the heating is possible, allowing adjustments to be made to the feed-stock at that time to control the chemistry of the product.
Electric Arc Furnace. The electric arc furnace is a large kettle-shaped chamber lined with fire brick, into which a charge of steel scrap with coke is melted by means of heat produced by an electric arc. Since no burning of fuel is required, the oxygen of the steel can be controlled and kept to a minimum. Alloying elements can be added without the fear of oxidation. Because of the control of heat time, temperature,
and chemistry, the electric arc furnace is used in the production of high-quality alloy steels.
Argon Oxygen Process. The argon oxygen process (AOP) is used in the production of specialty steels with low carbon and sulfur and high chromium content. A charge of steel of almost the desired properties is introduced into a basic oxygen furnacelike vessel, and controlled amounts of oxygen and argon are introduced into the melt. This reducing process conserves valuable chromium.
Vacuum Degassing Process. When exceptionally high quality steel is required, steel can be ‘‘degassed’’ in a vacuum environment. This vacuum degassing process provides strong reduction in hydrogen, oxygen, nitrogen, inclusions, and contaminants such as lead, copper, tin, and arsenic.
Ingots, Blooms, and Billets. Ingots, blooms, and billets are the shapes into which the molten metal is solidified before using it in a particular pipe-making (or other) process. An ingot is poured from the molten steel and after solidification goes to the blooming mill to be rolled into square blooms, which are further formed onto bar rounds. Alternately, in the case of large pipe, the ingot may be formed into pierced billets to be used in the seamless tube-making process.
Continuous Casting Process. Although the development of the continuous casting process (Fig. A5.2) began in the nineteenth century, it was after World War II that its use became of great commercial interest. In the continuous casting process, molten steel is poured from the melting furnace to a ladle feeding a reservoir called a tundish. The tundish feeds a lubricated mold that has a cooled copper surface, and the solidifying steel is continuously drawn from the mold. In the case of piping steel, the mold is the shape of the billet or slab used in the tube-making process. There are many types of continuous casting processes, ranging from vertical to horizontal, with variations of bent sections in between. This process is now used in more than half the world’s steel production. In Japan, 85 percent of the total steel produced is by the continuous casting process.
Iron-Making
The making of steel for ferritic piping begins with the smelting of iron ore found in deposits in the crust of the earth throughout the world in forms such as hematite and magnetite. In preparation for the smelting process, the iron ore may be treated by any of several methods to convert it into a suitable form for introduction into the blast furnaces. One method is sintering, which converts ores into a porous mass called clinkers. Another is smelting, which is performed in a blast furnace. The process involves the chemical reaction of iron ore with limestone, coke, and air under heat, reducing the iron ore to iron. The ‘‘pig’’ iron obtained from the blast furnace is used as the basic component in the steel-making process.
Steel-Making
Steel for piping can be produced in several ways (Fig. A5.1), depending on the facilities available and the desired characteristic of the steel.Generally, steel requires the removal of carbon from the pig iron to a degree required by the carbon steel properties desired. Alloy steel also requires the addition of alloying elements such as chromium, nickel, manganese, and molybdenum to provide the special properties
associated with the alloying element.
Bessemer Converter. The Bessemer method of making steel (due to Sir Henry Bessemer in 1856) consisted of blowing a current of cold air through the molten pig iron, thereby using the oxygen in the air to burn carbon and other impurities from the melt. After burning out the carbon in the pig iron, the exact amount of carbon required for the steel is reintroduced into the heat.
Basic Oxygen Process. The basic oxygen process (BOP) is essentially the same as the Bessemer process except that it uses pure oxygen (instead of air) together with burned lime converted from limestone. This process burns out the impurities more quickly and completely and provides for more precise control of the steel chemistry.
Open-Hearth Furnace. The open-hearth furnace is used to produce much of the steel in the United States; however, it is being superseded by the basic oxygen process. Its significant advantage is the ability to use scrap steel as well as pig iron as ferrous stock in producing steel. The open-hearth furnace is a large rectangular brick floor, or hearth, completely covered with a brick structure through which the
charge of ferrous stock and limestone is introduced. It is fueled with coke gas, oil, or tar introduced through a burner playing a flame across the hearth while the products of combustion escape through the furnace wall away from the burner. An advantage of the open-hearth process is that testing for carbon content during the heating is possible, allowing adjustments to be made to the feed-stock at that time to control the chemistry of the product.
Electric Arc Furnace. The electric arc furnace is a large kettle-shaped chamber lined with fire brick, into which a charge of steel scrap with coke is melted by means of heat produced by an electric arc. Since no burning of fuel is required, the oxygen of the steel can be controlled and kept to a minimum. Alloying elements can be added without the fear of oxidation. Because of the control of heat time, temperature,
and chemistry, the electric arc furnace is used in the production of high-quality alloy steels.
Argon Oxygen Process. The argon oxygen process (AOP) is used in the production of specialty steels with low carbon and sulfur and high chromium content. A charge of steel of almost the desired properties is introduced into a basic oxygen furnacelike vessel, and controlled amounts of oxygen and argon are introduced into the melt. This reducing process conserves valuable chromium.
Vacuum Degassing Process. When exceptionally high quality steel is required, steel can be ‘‘degassed’’ in a vacuum environment. This vacuum degassing process provides strong reduction in hydrogen, oxygen, nitrogen, inclusions, and contaminants such as lead, copper, tin, and arsenic.
Ingots, Blooms, and Billets. Ingots, blooms, and billets are the shapes into which the molten metal is solidified before using it in a particular pipe-making (or other) process. An ingot is poured from the molten steel and after solidification goes to the blooming mill to be rolled into square blooms, which are further formed onto bar rounds. Alternately, in the case of large pipe, the ingot may be formed into pierced billets to be used in the seamless tube-making process.
Continuous Casting Process. Although the development of the continuous casting process (Fig. A5.2) began in the nineteenth century, it was after World War II that its use became of great commercial interest. In the continuous casting process, molten steel is poured from the melting furnace to a ladle feeding a reservoir called a tundish. The tundish feeds a lubricated mold that has a cooled copper surface, and the solidifying steel is continuously drawn from the mold. In the case of piping steel, the mold is the shape of the billet or slab used in the tube-making process. There are many types of continuous casting processes, ranging from vertical to horizontal, with variations of bent sections in between. This process is now used in more than half the world’s steel production. In Japan, 85 percent of the total steel produced is by the continuous casting process.
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