The Four Methods of Manufacturing Pipes
Pipe manufacturing refers to how the individual pieces of pipe are made in a pipe mill; it does not refer to how the pieces are connected in the field to form a continuous pipeline. Each piece of pipe produced by a pipe mill is called a joint or a length (regardless of its measured length). In some cases, pipe is shipped to the pipeline construction site as "double joints," where two pieces of pipe are pre-welded together to save time. Most of the pipe used for oil and gas pipelines is seamless or longitudinally welded, although spirally welded pipe is common for larger diameters.


Four Types of Manufacturing
Longitudinally Welded SAW Pipe
Welded pipe (pipe manufactured with a weld) is a tubular product made out of flat plates, known as skelp, that are formed, bent and prepared for welding. The most popular process for large diameter pipe uses a longitudinal seam weld. Double submerged arc welded (DSAW) pipe is welded pipe whose longitudinal butt joint is welded in at least two passes, one of which is on the inside of the pipe; the welds are made by heating with an electric arc between the bare metal electrode. Pressure is not used. Filler metal for the welds is obtained from the electrodes. For diameters above 36 inches, double seam welded pipe is specified as an alternative in API 5L. This has two longitudinal seams 180° apart, formed by the SAW process. Finished pipes are normally 40 feet (12 m) and occasionally 60 feet (18 m) long, depending on the capacity of the pipe mill and the ease of transport to the pipeline.

Spiral Welded Pipe
As an alternative process, spiral weld construction allows large diameter pipe to be produced from narrower plates or skelp. The defects that occur in spiral welded pipe are mainly those associated with the SAW weld, and are similar in nature to those for longitudinally welded SAW pipe. An additional problem with early spiral welded pipe was poor dimensional accuracy, particularly out of roundness at the pipe ends. This led to problems of poor fit-up during field girth welding. Spiral linepipe gained a poor reputation in some companies as a result of these early experiences, and it was considered suitable only for low pressure applications such as water pipe. However, modern spiral linepipe from a premium quality supplier is of a quality equivalent to straight seam welded pipe, and it has been used extensively in Canada and Europe for high pressure gas pipelines in grades up to API X70.

Seamless Pipe
Plug Mill
This process is used to make larger sizes of seamless pipe, typically 6 to 16 inches (150 to 400 mm) diameter. An ingot of steel weighing up to two tons is heated to 2,370 °F (1,300 °C) and pierced. The hole in the hollow shell is enlarged on a rotary elongator, resulting in a short thick-walled tube known as a bloom. An internal plug approximately the same diameter as the finished diameter of the pipe is then forced through the bloom. The bloom containing the plug is then passed between the rolls of the plug mill. Rotation of the rolls reduces the wall thickness. The tube is rotated through 90° for each pass through the plug mill to ensure roundness. The tube is then passed through a reeling mill and reducing mill to even out the wall thickness and produce the finished dimensions. The tube is then cut to length before heat treatment, final straightening, inspection, and hydrostatic testing.
Mandrel Mill
This process is used to make smaller sizes of seamless pipe, typically 1 to 6 inches (25 to 150 mm) diameter. The ingot of steel is heated to 2,370 °F (1,300 °C) and pierced. A mandrel is inserted into the tube and the assembly is passed through a rolling (mandrel) mill. Unlike the plug mill, the mandrel mill reduces wall thickness continuously with a series of pairs of curved rollers set at 90° angles to each other. After reheating, the pipe is passed through a multi -stand stretch-reducing mill to reduce the diameter to the finished diameter. The pipe is then cut to length before heat treatment, final straightening, inspection, and hydrostatic testing.
Extrusion
This process is used for small diameter tubes only. The bar stock is cut to length and heated to 2,280 °F (1,250 °C) before being sized and descaled. The billet is then extruded through a steel die. After extrusion, the final tube dimensions and surface quality are obtained with a multi-stand reducing mill.

Electric Resistance Weld Pipe :

ElectricElectric Resistance Weld pipe is normally produced in sizes from 2 3/8 inch OD thru 24 inch OD.

ERW is produced from individual sheets or continuously from rolls of skelp. There are two important differences in the production of ERW pipe as versus CW pipe. ERW pipe is cold formed into a cylindrical shape rather than hot formed. An electric current rather than a flame is used to heat the edges of the strip for the fusion weld. Revolving copper discs serve as electrodes and raise the temperature to about 2600°F for effective welding. As in CW pipe, no extraneous metal is added; in fact, due to the extreme pressure of the rolls, steel is extruded on both the inside and outside of the pipe at the point of the weld. This is called flash and is removed on the O.D. by stationary cutters while still white-hot for A252 grades, and both the I.D. and O.D. for other grades. As in CW production, ERW pipe is subject to numerous finishing operations. ERW pipe is primarily used as API Line pipe for the transmission of gas and oil. It is also used for the transmission of water, under AWWA specifications, as piling and slurry pipe and in mechanical applications.

ERW pipe is available in the following most common specifications:
ASTM A-53 Grade A & B; A-135; A-252 Grade 1,2,3; API5L Grade A & B; and API5LX42 thru X-80

ERW pipe is available in lengths from single random to 120 feet depending on mill capability. Maverick Tube produces lengths up to 85 ft. in one piece. ERW pipe is available with square ends or beveled for welding, threaded and coupled and victaulic grooved. Surface finish are available in black or bare, or with protective coatings.

Major purchasers of ERW pipe are:
Utility Companies, Oil Companies, Steel Fabricators, Piling Contractors, Dredging Contractors, Water Well Contractors, Pipe Distributors, Pipe Line Companies, and Federal, State, and Local Governmental Agencies.

Characteristics
The high frequency electricity-resistant welding method developed by ABBEY ETNA of the United States is adopted in the production of our ERW pipes. Thermatool's technology renders superb weldability to our products. Preference of our ERW pipes over any other product is attributed to its wide range of applications.

Superior Quality
We produces pipes of outstanding quality. The rigorous quality control and 22 years of accumulated know-how and technology are contributors behind our top-quality products.