There are several key differences between pipes and tubes, however the most well known is the way in which the size measurements are designated: tube is designated based on outside diameter (OD) and pipe is based on inner diameter (ID). In addition, pipes are typically used as vessels, meaning for the transfer of fluids or gases, while tubes are generally structural or used as support.
Fabricated for a number of purposes, pipes are capable of fulfilling needs in many industries including: wastewater, for water treatment facilities and water pump stations; industrial manufacturing, for heat exchanger shells, waste treatment and cooling towers; petrochemical, for chemical processing and oil pipelines; and mining, for mine dewatering, depressurization and dust suppression.
Additionally, pipes are also used in power plants, architectural, food processing and pharmaceutical applications. Some of the broad spectrum of materials that are used to fabricate pipe include carbon steel, stainless steel, ductile iron, titanium, brass, polyvinyl chloride (PVC), high density polyethylene (HDPE), polypropylene (PP), ceramics and concrete; however, steel and iron are the most common metals and PVC is the most common plastic material.
Pipe fabrication processes include many diverse processes that take place after or during pipe formation in order to customize the pipe for its intended application. As a result, many pipe fabricators are not involved in the actual formation of raw metal materials into pipes; however, it is still highly important. Most commonly, pipes are created through a fairly simple process referred to as plate rolling, in which flat metal plate is rolled and then welded at the seam through either electric resistance welding (ERW) or electric fusion welding (EFW).
After formation, pipes can undergo fabrication processes such as bending, spooling, flanging and cutting. Pipe bending can refer to both cold and hot working processes that bend pipes using computer-controlled machines to ensure the quality and efficiency of a product. Pipe spooling is the process of enhancing the pipe’s ability to connect to other pipes or components through winding a long, continuous section of pipe onto a cylinder from which it can easily be dispensed.
Another customizing process, pipe flanging is done to create a projection around the end of the pipe either for increased strength or in order to attach to another component. Pipe cutting is the process in which pipes are cut through the use of cut-off saws, horizontal band saws, lathes or lasers so that they will better fit within the required dimensions.