Welded Pipes are manufactured from Plate or from continues Coil or strips. To manufactured welded pipe, first, Plate or coil is rolled in the circular section with the help of plate bending machine or by a roller in the case of continues process.
Once the circular section is rolled from the plate, in second step pipe is weld with the help of welding setup. A pipe can be welded with or without filler material using appropriate welding method. Welded pipes are cheaper as compared to a seamless pipe and also weak due to the weld joint. Welded pipes can be manufactured in large size without any upper restriction. Welded pipes with filler material can be used in the manufacturing of long radius bends and elbow.
Here, I have shown you a forming of the plate by rolling machine. In this methods, the plate is placed in between the pair of rollers. The plate is formed in circular section by gradually applying the load on the top roller and rotating the plate. This method is used for manufacturing of higher thickness SAW pipes. Instead of the roller, point pressing method which also known as UO methods can also be used to form a circular section from the plate. UO means first you made u shape & then O shape.
SAW Welded Pipes Manufacturing Method
In single seam SAW pipe, wedding is done with the help of submerged arc welding process. In this method, a welding arc is submerged in welding flux. A Continues solid filler wire is fed from the outside. The pipe is welded first inside and then from the outside.
In the case of double seam saw pipe first two halves are joined by tack weld which is called fit-up. Double seam saw pipe is havening a two weld seam opposite to each other. Both the seams are welded from inside and outside of the pipe. In the case of high thickness pipe, multiple pass welding is done.
In a spiral saw pipe, steel plate from the de-coiler is formed in a spiral loop. This spiral loop is then welded from inside and outside of the pipe. Because of the method of manufacture, a wide variety of diameters can be produced. Spiral saw pipes are used for low-pressure services.
Whereas straight saw pipes are used for medium to high-pressure services. Spiral saw pipes are less costly compared to straight saw pipe.
Once the welding is completed heat treatment is carried out on the weld or on the full body of pipe, this depends on the thickness of pipes. Weld seams are also subjected to various non-destructive testing such as RT & UT to ensure the soundness of the weld material.
Once all NDT is completed pipes are hydro tested to ensure strength and ability to remain leak proof under pressure. In the last stage of inspection, the pipe is checked visually and dimensionally by competent inspection engineer. He will ensure that pipe is meeting the code, standard, and specification requirements. Once the Inspection engineer cleared the pipe, it will mark as per the standard requirements & send for the packaging.
ERW / EFW or HFW Welded Pipes Manufacturing Process
Less thickness pipe, mainly ERW / EFW or HFW welded pipes are formed by continues rolling method. In this method, a flat metal strip from the strip coil is feed into the series of roller assembled in line. These rollers gradually form the strip in the circular section. At the end of rolling assembly, this pipe is continuously welded by welding machine.
ERW/EFW and HFW are welding methods in which pipe is welded without adding filler material. However, EFW welding method can be used with filler material also.
ERW Pipe Manufacturing Process
In ERW welding, two electrodes, usually made from copper, are used to apply pressure and current. The electrodes are disc shaped and rotate as the material passes between them. This allows the electrodes to stay in constant contact with the material to make long continuous welds.
A welding transformer supplies low voltage, high current AC power. The joint of the pipe has high electrical resistance relative to the rest of the circuit and is heated to its melting point by the current. The semi-molten surfaces are pressed together with a force that creates a fusion bond, resulting in a uniformly welded structure.
HFW Pipe Manufacturing Process
In HFW welding, a high-frequency current is used to create weld joints. Whereas, in EFW welding process, the external high energy electric arc is used to create a weld joint. Once the welding is done, the excess weld material from outside and inside of the pipe is removed with the help of trimmer tools.
In general, to reduce the negative effect of welding, a localized heat treatment of weld seam is carried out immediately it clears online ultrasonic test. Normally an induction heating method is used to restore microstructure of welded zone. These type of heat treatment is known as post annealing. In next stage, the pipe will go through Hydro testing, visual and dimensional inspection and once certified by inspection engineer it will send for packaging. This is all about welded pipe manufacturing process.
This article comes from hardhatengineer edit released