Steel Pipe & Tubing - All You Need to Know
Date:2020-11-27
Steel Pipe & Tubing seem similar at first blush and in fact they share many characteristics but they also have some important
Steel Pipe & Tubing seem similar at first blush and in fact they share many characteristics but they also have some important differences.
Definitions:
Steel Tubing is a hollow steel shape intended for structural purposes and made from carbon, stainless, or galvanized steel further divided as:
Mechanical Tubing is used in low stress applications such as fences, kitchens, restaurants, hospitals, solar panels and made with wall thicknesses up to 10 gauge.
Structural Tubing is for high stress structural application like bridges, buildings, roll cages, and underwater platforms with wall thickness from 3/16" and up. It is often referred to as Hollow Structural Sections or just the acronym HSS.
Pipe is a hollow structure that is intended to carry material such as liquids, gasses, or even solids. Its wall thickness is described by its Schedule and it is often broken down by type using the method of manufacturing it, either ERW or Seamless
How it's made:
Both Tubing and Pipe are manufactured by the first two methods below. The third is reserved for Tubing only.
Electric Resistance Welded, often abbreviated as ERW, is a process that uses specific machinery to shape the pipe and tubing. A continuous steel sheet is unwound from a coil and shaped using contoured rollers, forcing the edges together under pressure. These edges are then welded together by heating the material to over 2,000 degrees. After welding, the pipe or tubing is cut into the exact size needed.
Seamless Pipe (and tubing) is made by extruding a steel block or by drilling a solid steel bar. Next, the extrusion or the drilled steel bar is cold drawn through a dye to achieve the diameter and thickness needed. Because this process can cause mechanical hardening, sometimes the material is annealed and straightened as a final process. Seamless Pipe & Tubing is subdivided as:
Cold Drawn Seamless, or CDS, exhibits precise tolerances and a good surface finish.
Hot Finished Seamless, or HFS, has less critical tolerances and somewhat scaly finish and is not as strong as CDS.
For Drawn over Mandrel, or DOM tubing, the first stages of manufacturing are identical to ones used to make electric resistance welded tubing, but in the finishing stages the entire flash weld is taken out and the tube is cold drawn over a mandrel. A mandrel is a round object against which material can be forged or shaped. The cold drawn process provides the tube with better dimensional tolerances, improved surface finish and the strongest weld strength achievable.
Pipe Sizes:
Pipe Size is specified with two non-dimensional numbers:
•Nominal Pipe Size (NPS) for diameter based on inches.
•Schedule Number (SCH to specify the wall thickness of the Pipe.
Both the size and schedule are required to accurately specify a particular piece of pipe.
Nominal Pipe Size (NPS) is the current North American Set of standard sizes for pipes used for high and low pressures and temperatures. A further discussion of this is here.
Iron Pipe Size (IPS) was an earlier standard than NPS to designate the size. The size was the approximate inside diameter of the pipe in inches. Each pipe had one thickness, named (STD) Standard or (STD.WT.) Standard Weight. There were only 3 wall thicknesses at the time. In March 1927, the American Standards Association created a system that designated wall thickness based on smaller steps between sizes and introduced Nominal Pipe Size which replaced Iron Pipe Size.
Schedule Number for wall thickness ranges from SCH 5, 5S, 10, 10S, 20, 30, 40, 40S, 60, 80, 80S, 100, 120, 140, 160, STD, XS (Extra Strong) AND XXS (Double Extra Strong).
