During the Saturday, I have to train two of the supervisor in the factory so they can use the computer properly without having trouble in the future, and I hope they can operate the computer well. and now is the time that I have to post Piping and Fabrication blog and here the rest of the post.
Welded Pipe. Welded pipe is produced by forming a cylinder from flat steel sheets coming from a hot strip mill. The strip mill takes the square bloom from the blooming mill and reduces it into plates, skelp, or coils of strip steel to be fed into the particular welding process equipment.Butt-weld pipe ismade by furnace heating and forge welding or by fusion welding using electric resistance, flash, submergedarc welding, inert-gas tungsten-arc welding, or gas-shielded consumable metal-arc welding. The welded seam is either parallel to the tube axis or in a spiral direction about the tube centerline.
Furnace-Welded (Continuous or Butt-Welded) Pipe. This is a low-cost carbon steel pipe below 4-in diameter made of steel from open-hearth or basic oxygen Bessemer steel. In this process, skelp is heated to welding temperature in a continuous furnace and passed through forming and welding rolls, welding the strip edges at the same time the tube is formed. Strips can be consecutively resistance-welded to each other to form a continuous pipe.
Fusion-Welded Pipe. Fusion-welded pipe is produced by resistance-welding, induction-welding, or arc-welding. Electric Resistance-Welded Pipe. In the electric resistance-welded (ERW) pipe process (Fig. A5.9), upon exiting the forming mill, the longitudinal edges of the cylinder formed are welded by flash-welding, low-frequency resistance-welding, high-frequency induction-welding, or high-frequency resistance-welding. All processes begin with the forming of the cylinder with the longitudinal seam butt edges ready to be welded.
In the flash-welding process, the butted cylinder surfaces are placed in contact; a voltage is applied across the contact, causing metal flashing along the seam length and raising the steel temperature locally to the metal-forming temperature. After this, the seam edges are pressed together and a pressure fusion-weld is formed at a temperature lower than the steel melting point. The upset material along both the inside and outside of the seam is removed with a scarfing tool. This process is used to produce high-strength carbon steel pipe from NPS 4 to 36 (DN 100 to 900).
In the low-frequency resistance method, electric current and pressure are simultaneously applied, and the resulting heat causes melting of the edges. The resulting seam is similar to that from the flash-welding process and requires removal of the upset material. Postweld heat treatment may be desirable for stress relief, tempering, or recrystallization. This process is applied to pipe of outside diameters up to NPS 22 (DN 550).
High-frequency welding process, using an alternating current of more than 400,000 Hz, is similar to the low-frequency resistance welding process. The lower inductance path followed by the current produces a smaller high-temperature band that minimizes the amount of upset material. This process is used for pipe up to NPS 42 (DN 1050).
For production of small-diameter pipe at high rates of production, the highfrequency induction-welding process may be used. In this process, an induction coil raises the seam temperature to welding temperature. The rapid increase in temperature caused by the high-frequency current causes little upsetting because of the resulting control of temperature and fusion. Several arc-welding processes are used in commercial welded pipe production. These include the submerged-arc-welding process, the inert-gas tungsten-arc-welding process, and the gas-shielded consumable metal-arc-welding process. In the submerged-arc-welding process, bare wire consumable electrodes are added to the weldmetal under a blanket of flux. Themelting flux creates a protective atmosphere of inert gas and a slag blanket over the solidifying weld metal. In heavywall piping, simultaneous submerged arc seam welds on inner and outer sides of the pipe are sometimes used to build up the weld thickness to the desired level. In modern pipe production facilities, automated equipment is used to control all variables in the submerged arc process, including relative movement speed between pipe and welding heads, wire feed rate, welding current, and flux feed rate. Submerged-arc seam-welded pipe is used in critical high-temperature or high-pressure applications in the electrical power generation process and chemical industries.
For carbon steel and stainless steel pipe of smaller wall thickness, the inert-gas tungsten-arc-welding process is used. The weld is protected by an inert gas such as argon or helium, which forms a blanket over the weld metal. For thicker-wall pipe, a filler wire may be fed into the protective gas blanket. For thin-wall pipe, no filler is used. A number of variations in pipe forming before welding are used, including molding, pressing, or rolling strip into cylinders.
Spiral Welded Pipe. Lightweight pipe for temporary or light operation duty such as in water systems applications may be made by the spiral-welded process. In this process, narrow strips of steel sheet are helically wound into cylinders. The edges of this strip can either be butting or overlapping and are welded by any of several electric arc-welding processes.
Furnace-Welded (Continuous or Butt-Welded) Pipe. This is a low-cost carbon steel pipe below 4-in diameter made of steel from open-hearth or basic oxygen Bessemer steel. In this process, skelp is heated to welding temperature in a continuous furnace and passed through forming and welding rolls, welding the strip edges at the same time the tube is formed. Strips can be consecutively resistance-welded to each other to form a continuous pipe.
Fusion-Welded Pipe. Fusion-welded pipe is produced by resistance-welding, induction-welding, or arc-welding. Electric Resistance-Welded Pipe. In the electric resistance-welded (ERW) pipe process (Fig. A5.9), upon exiting the forming mill, the longitudinal edges of the cylinder formed are welded by flash-welding, low-frequency resistance-welding, high-frequency induction-welding, or high-frequency resistance-welding. All processes begin with the forming of the cylinder with the longitudinal seam butt edges ready to be welded.
In the flash-welding process, the butted cylinder surfaces are placed in contact; a voltage is applied across the contact, causing metal flashing along the seam length and raising the steel temperature locally to the metal-forming temperature. After this, the seam edges are pressed together and a pressure fusion-weld is formed at a temperature lower than the steel melting point. The upset material along both the inside and outside of the seam is removed with a scarfing tool. This process is used to produce high-strength carbon steel pipe from NPS 4 to 36 (DN 100 to 900).
In the low-frequency resistance method, electric current and pressure are simultaneously applied, and the resulting heat causes melting of the edges. The resulting seam is similar to that from the flash-welding process and requires removal of the upset material. Postweld heat treatment may be desirable for stress relief, tempering, or recrystallization. This process is applied to pipe of outside diameters up to NPS 22 (DN 550).
High-frequency welding process, using an alternating current of more than 400,000 Hz, is similar to the low-frequency resistance welding process. The lower inductance path followed by the current produces a smaller high-temperature band that minimizes the amount of upset material. This process is used for pipe up to NPS 42 (DN 1050).
For production of small-diameter pipe at high rates of production, the highfrequency induction-welding process may be used. In this process, an induction coil raises the seam temperature to welding temperature. The rapid increase in temperature caused by the high-frequency current causes little upsetting because of the resulting control of temperature and fusion. Several arc-welding processes are used in commercial welded pipe production. These include the submerged-arc-welding process, the inert-gas tungsten-arc-welding process, and the gas-shielded consumable metal-arc-welding process. In the submerged-arc-welding process, bare wire consumable electrodes are added to the weldmetal under a blanket of flux. Themelting flux creates a protective atmosphere of inert gas and a slag blanket over the solidifying weld metal. In heavywall piping, simultaneous submerged arc seam welds on inner and outer sides of the pipe are sometimes used to build up the weld thickness to the desired level. In modern pipe production facilities, automated equipment is used to control all variables in the submerged arc process, including relative movement speed between pipe and welding heads, wire feed rate, welding current, and flux feed rate. Submerged-arc seam-welded pipe is used in critical high-temperature or high-pressure applications in the electrical power generation process and chemical industries.
For carbon steel and stainless steel pipe of smaller wall thickness, the inert-gas tungsten-arc-welding process is used. The weld is protected by an inert gas such as argon or helium, which forms a blanket over the weld metal. For thicker-wall pipe, a filler wire may be fed into the protective gas blanket. For thin-wall pipe, no filler is used. A number of variations in pipe forming before welding are used, including molding, pressing, or rolling strip into cylinders.
Spiral Welded Pipe. Lightweight pipe for temporary or light operation duty such as in water systems applications may be made by the spiral-welded process. In this process, narrow strips of steel sheet are helically wound into cylinders. The edges of this strip can either be butting or overlapping and are welded by any of several electric arc-welding processes.
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