Welded tubes and pipes are formed by shaping and welding HR coil or steel plate, and as such are produced from flat products as opposed the billet or ingot products used to produce seamless pipe. Welded tube and pipe is made to the specifications for grades that serve consuming markets including manufacturing, automotive/ aerospace, construction, structural, decorative, oil and gas drilling, oil, gas and water transmission, geological research, power generation and refineries.
Methods of Production
There are 3 main methods of production for welded tube and pipe electric-resistance (ERW), longitudinal (LSAW or DSAW), and spiral welded.
Electric-resistance welded (ERW) tube and pipe is made by longitudinally welding HR coil. ERW material is typically limited to a maximum of 24 in diameter, due to the typical width of HR coil (maximum of 76 or 2.25m) with an average pipe length of 18m to 24m and a maximum wall thickness of 25mm.
2. Longitudinal welded
Heavy plate is primarily used as the substrate, which is welded using the submerged arc welded (SAW) method, or double submerged arc welded (DSAW). Longitudinal welded pipe is created with a straight seam welded along the length of the pipe. Common pipe lengths are 12m to 18m although new production methods can go longer. There are 3 manufacturing routes for this type of pipe:
- UOE- The flat plate is pressed and bent into a U shape and then into an O shape. The pipe is welded and expand (E) into the proper diameter. The standard diameter ranges between 20-56, limited by the width of the substrate plate thickness.
- JCOE- The flat plate is pressed and bent into a J shape and then a C shape and closed into an O shape. Similar to UOE, the pipe is welded and then expanded (E) into the proper diameter. This manufacturing route is most popular in India and can have a maximum wall thickness of 60mm.
- Roll bending- The flat plate passes through a series of rollers that bend the pipe into an O shape. While this manufacturing technique is slower than UOE, the pipe can be produced with a larger diameter, up to 100 with an average length of 12m.
3. Spiral welded
Spiral welded is produced by winding and welding steel plate or thick HR coil in a circular fashion. This method allows for increased sizes and lengths. Diameters range between 24 200, while maximum wall thickness is about 20-25mm. The welding technique is referred to as Helical SAW (HSAW). Spiral welding is dominant in emerging markets and in new capacities in comparison to longitudinal pipe, as it is historically up to 15% less expensive to produce.
Welded Tube and Pipe Classifications
1. Welded linepipe
Welded linepipe is classified as any tube or pipe that carries liquids or gas across land, including oil, natural gas, or water. The pipe is laid in a horizontal direction, a key differences between linepipe and OCTG material. After production, tube and pipes are transported to the site and welded together to form the linepipe. The linepipe products are some of the highest priced of the steel products. They are classified under the American Petroleum Institute (API) specifications (API 5L).
2. Welded OCTG pipe
Oil country tubular goods (OCTG) pipe is used for carrying oil and gas in a vertical direction, as opposed to horizontal, once a new oil and gas rig has been drilled. Casing is used to protect the tubing, which runs inside the drilled hole, down to the oil or gas well. Tubing or lifting pipe runs down the middle of a well bringing liquid/ gas to the surface or injecting water into the well. Drill pipe is tube that is used to hold the drill bit or explosives. Welded OCTG tube and pipes are not welded together onsite, pipes are instead coupled together using threading techniques specific to the environment and substance being extracted. Welded OCTG pipes are classified under the American Petroleum Institute API with non-heat treated grades including J and K grades, the lowest API classification, and heat treated including N80 type Q, P110, L80. Heat treated grades are for drilling in more difficult or caustic environments.
Outside of North America, OCTG tubing and casing is dominated by seamless material, as opposed to welded OCTG. About 29% of the total OCTG market is welded pipe, while the remaining 71% of is seamless. NAFTA is the worlds largest market for OCTG products, representing 42% of global consumption in 2012.