<P> There are three processes for metallic pipe manufacture . Centrifugal casting of hot alloyed metal is one of the most prominent process . Ductile iron pipes are generally manufactured in such a fashion . Seamless (SMLS) pipe is formed by drawing a solid billet over a piercing rod to create the hollow shell . As the manufacturing process does not include any welding, seamless pipes are perceived to be stronger and more reliable . Historically, seamless pipe was regarded as withstanding pressure better than other types, and was often more available than welded pipe . </P> <P> Advances since the 1970s in materials, process control, and non-destructive testing, allow correctly specified welded pipe to replace seamless in many applications . Welded pipe is formed by rolling plate and welding the seam (usually by Electric resistance welding ("ERW"), or Electric Fusion Welding ("EFW")). The weld flash can be removed from both inner and outer surfaces using a scarfing blade . The weld zone can also be heat - treated to make the seam less visible . Welded pipe often have tighter dimensional tolerances than the seamless type, and can be cheaper to manufacture . </P> <P> There are a number of processes that may be used to produce ERW pipes . Each of these processes leads to coalescence or merging of steel components into pipes . Electric current is passed through the surfaces that have to be welded together; as the components being welded together resist the electric current, heat is generated which forms the weld . Pools of molten metal are formed where the two surfaces are connected as a strong electric current is passed through the metal; these pools of molten metal form the weld that binds the two abutted components . </P> <P> ERW pipes are manufactured from the longitudinal welding of steel . The welding process for ERW pipes is continuous, as opposed to welding of distinct sections at intervals . ERW process uses steel coil as feedstock . </P>

Steel industry manufacturing steel pipes is an example of