Stainless steel tubes are often used in applications that require rigid materials for potable water conveyance. Manufacturers select stainless steel because certain manmade materials have unwanted or unknown exposure effects while stainless steel has many desirable qualities for maintaining clean water. Steel tubes can also be used for structural support in buildings and vehicles. The terms “tube” and “pipe” are generally interchangeable, although technically, “tube” implies heightened engineering qualities. Tubes are generally manufactured based on standardized sizes.
Manufacturing Steel Tubes
There are three main methods of manufacturing tubing that lend their names to tubing classifications.
Seamless. Seamless steel tubes are produced through extrusion. Extruded tubes can be formed in a hot or cold process. Long sections of steel bar are forced through a die that blocks out the intended shape of the tube.
As-welded or electric resistant welded (ERW). This method involves passing a rolled sheet of steel through two weld rollers. The weld rollers have a groove around their circumference, through which the steel roll passes. There is a contact at the roll seam that transmits electricity at a high enough current to weld the seam closed. The resulting weld is very small.
Drawn-over-mandrel (DOM). A mandrel is a small piece of metal inserted into the tube to define a shape. It gives the tube extra support to prevent unwanted wrinkling during drawing. The tube is passed through a die that has a smaller diameter than the current tube size. As the tube is drawn, it shrinks to match the size of the die’s diameter. This process allows for tight tolerances and specifications.
Each of these manufacturing processes allows manufacturers the ability to form varying tube shapes and sizes. Tubes are not always cylindrical, and can be made in triangle, square or other polygonal shapes. Steel tubes destined for certain applications require extra processes as well. Applications involving hydrogen must be factory pre-cleaned or certified as instrument grade due to hydrogen’s reactive characteristics that can cause metal embrittlement or even explosions.
Generally, a steel tube manufacturing process is chosen for its interaction with the type of steel to be used. Certain types of steel react poorly to heat because of carbon content, so they can’t be easily welded. Steel types also play a role in decisions regarding use in volatile applications.
Steel Tube Applications
Steel tubing is used in high numbers in plumbing applications. The reasons are threefold. One, stainless steel is very sturdy, composed of 80-90 percent steel and 10-20 percent chromium. Steel tubing can handle the types of pressures exerted by water upon plumbing structures. Additionally, the surface of stainless steel does not allow for much adherence by particles or bacteria, so purification processes will not pass on unintended detritus. Finally, steel does not contaminate drinking water.
Steel tubes are also used in a wide variety of structural applications, such as industrial and residential construction. Examples include fences, gates, railings, playground and athletic equipment. Steel is often used for construction tubes over other metals like aluminum when extra stress resistance is necessary. Steel tubes can also be used in automotive applications and even as parts of furniture.