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Welded and Seamless Stainless Steel Tubing FabricationStainless steel tubing is often used in applications that depend on the material’s high corrosion resistance, versatility, and relatively low maintenance cost. Because tubing can serve a range of functions that require varying degrees of specification, several standards are in place to ensure the proper use and manufacture of different grades of stainless steel tubing. Although there are several such standards and specifications (for different grades of manufactured stainless steel tubing in certain applications), there are generally two major categories for tubes and piping: welded and seamless. Welded Stainless Steel Tubing  Welded stainless steel requires that alloys be melted according to certain specifications, depending on the grade and the application. The basic strip of stainless steel, from which the tubes are to be formed, is either a hot or cold formed coil. Depending on whether the tubing is hot or cold formed, the results will be different. Tubing made from cold formed stainless steel will have a smooth finish and strong mechanical traits, as well as closer tolerances than hot formed coil-based tubing. Regardless of whether the stainless steel is hot or cold rolled coil, the welding process is the same. First, the coils are separated into designated widths. Next, forming processes are applied. In order to seal the seams of each formed tube, welding rolls are used. (Rolls are also used to prevent tearing during welding). Once the weld is complete, weld bead conditioning can begin. For thin-wall tubes, this entails weld forgiving. For thicker wall tubes, weld rolldown is typically applied. After this step is complete, the tubes are then sized, which ensures that the tube meets the proper designated dimensions including diameter, roundness, and straightness. To establish the final length of the tubing, the tube must be cut (this step is often called cutoff). Cutoff can be achieved in several ways, but abrasive cutting is a common choice because it does not require a size change with each tube as a die does. Shear cutting is also a common choice because it protects the tube’s integrity during cutoff, ensuring the part doesn’t become warped or misshapen.  Seamless Stainless Steel TubingIn cases where welding isn’t used, seamless stainless steel tubing can be manufactured using extrusion, piercing, or gun drilling. Piercing uses a stainless steel metal bar as its base material, then pierces a hole in the bar. The bar is then rolled and heated to assume a tubular form. However, piercing is not effective for metal bars that contain more than 12 percent chromium. In extrusion, a stainless steel bar is fed into a tube and worked through a die, a process that is commonly used because it doesn’t discriminate against metal content and can produce tubes effectively and efficiently. However, the extrusion process requires a bit more preparation than piercing does. Gun drilling, a third manufacturing option for seamless steel tubing, produces the highest-quality tubes. The process requires a round metal bar be inserted into a straight flute drill. Although the process is more expensive than other options, the resulting tubes typically outperform those manufactured by other means. In certain cases, cold forming may be required if the tubing has unusual dimensions or a rare composition. Cold drawing, which involves the use of a die to alter tubing’s shape, is one such method. Cold pilgering, which reduces overall wall thickness, is another cold forming method that may be used. Both processes are not usually necessary in manufacturing stainless steel tubing, but are the preferred cold forming methods when applications require it. Other Pumps, Valves & Accessories Guides
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