Stainless steel is a versatile steel alloy comprised of a percentage of chromium, which provides the material its corrosion resistance and the trait that gives stainless steel its name. There are many grades of stainless steel, but all must have a minimum chromium content of at least 10.5 percent and can range upwards of 20 percent depending on the application’s needs. The material is known for its excellent oxidation resistance, durability, and low maintenance, which is why it is widely used in producing a large and diverse array of parts and components in many industries. This makes understanding stainless steel tube fabrication an essential part of the purchasing process.
Stainless steel tubing is one such product manufactured from the alloy for applications requiring such properties as strength, hygiene, corrosion resistance, or heat resistance. Tubing can be made to various sizes and lengths for mechanical operations, aerospace applications, heat exchangers, condensers, medical devices and components, instrumentation, and other structural functions.
Tubing vs. Piping
Stainless steel tubes are closed-shaped, elongated structures that can be round, square, rectangular, or manufactured to meet a particular component’s design needs. It’s important to note that stainless steel tubing should not be confused with stainless steel piping. Though similar in appearance, tubing is measured by the outside diameter for use in building structures and components, whereas the inside diameter measures piping because they are important in the transport and flow of fluids such as gas and fuel, steam, and other liquids.
Creating the Raw Material
The manufacturing process for seamless stainless steel tubing is a multi-step process. It begins with the creation of ingots from an electric arc furnace. The large castings are derived from iron ore and coke, a carbon-rich substance in heated coal. The two materials are heated to a liquid substance to create steel. Chromium is added (and other metals as required) and then cooled into ingots that can be used for storage or transporting materials to manufacture. The steel can also be cast as a bloom to be rolled in a billet to form a “rough” tube.
Tubing Manufacturing Methods
The manufacturing of seamless stainless steel tubing can be accomplished by several methods. However, there are two popular methods:
Rotary Piercing and Rolling
Rotary piercing and rolling are produced when the stainless steel material of a proper weight, diameter, and grade is heated to a suitable forging temperature. The steel is then pierced and worked on with several types of mills. Doing so causes the heated material to flow around a piercer point resulting in a hollow billet, which is then roller elongated in a succession of mills. A mandrel or plug forms the tubing’s internal support; elongated tubing can be further sized by rolling without internal support.
Extrusion
As with rotary piercing and rolling, extrusion processes begin with stainless steel of the desired grade, diameter, and weight. The extrusion process is ideal for forming long-length, seamless stainless steel coil tubing. It provides the most concentric ID (inside diameter) and uniform OD (outside diameter). Beginning as a hot extruded seamless pipe, the raw material is first cold reduced and then processed through cold pilger into long straight forms.
Cold pilgering is a cold-rolling, longitudinal process that works the tubing to the desired dimensions (OD, ID and wall thickness) in one step. During cold pilgering there is hardly any loss of material. But for the end facing of the tubes that need to be finished or cut off.
Final Processing & Fabrication
Once the cold reducing has been performed, the stainless steel tubing is annealed to remove any possible internal stresses and restore the material’s crystalline structure for further cold working. Annealing also softens the cold-worked and brittle material to return its ductile properties.
Contact the Experts at Atlantic Stainless
Atlantic Stainless supplies the widest variety of high-quality stainless steel products, including stainless steel tubing, piping, sheets, and much more, in addition to offering stainless steel cutting, shearing, and polishing services.
To order stainless steel tubing or learn more about stainless steel tube fabrication, please contact us today.
