The Basics of Buying Steel Pipe
There are several variables to consider when buying steel pipe, including the pipe dimension, thickness, and coating, whether the pipe is seamless, straight weld or spiral weld, and whether to purchase new pipe or surplus pipe.
Steel Pipe Wall Thickness
Steel pipe walls come in three main thickness options: standard (STD), extra strong (XS) and double extra strong (XXS). For example, a steel pipe manufacturer might offer a 10-inch steel pipe with a standard wall thickness of 0.365 inches, an extra strong wall thickness of 0.5 inches, and a double extra strong wall thickness of 1 inch. The best pipe thickness to choose will vary depending on the project requirements and how much stress the pipe is expected to withstand.
Small Diameter vs. Large Diameter Steel Pipe
Because steel is malleable and durable, it can be used to make pipe in a wide range of sizes. Small diameter steel pipe can range from the 1.5 inch tubing used for things like hydraulic lines and instrumentation tubes to the smallest hypodermic needle, which has an inner diameter of 0.0826mm. Conversely, large diameter steel pipe—such as the pipe used in shipbuilding and the oil and gas industry—starts at about 14 inches and increases up to 36 inches and larger.
Steel Pipe Coating Options
Because steel pipe is prone to oxidation and corrosion, the steel must be protected. One of the most popular and cost effective ways to protect steel pipe is to coat the pipe in a protective finish. Common coating options include fusion bond epoxy, SynergyTM coating, scotch coating/fletcher coating, and galvanizing. Each of these options varies in their use and application, and different coatings will work better in different environments.
Surplus vs. New Steel Pipe
Surplus steel pipe is pipe that has been used before and is being resold. It’s a common misconception that surplus steel pipe must be old or corroded, but this isn’t always the case. Sometimes surplus steel pipe is brand new. New steel pipe might be sold as “used” or “surplus” if the pipe was left over from another project, such as in instances where more pipe was ordered than needed, or where scraps of pipe were left over from being cut. Surplus steel pipe is a cost effective option that works well for light duty structural applications, road bore casings, temporary drainage projects, and more. Surplus steel pipe should only be used for projects where it is both legal and safe; if safety issues arise, then it is best to use new steel pipe.
Seamless vs. Straight Weld vs. Spiral Weld
The three main styles of steel pipe are seamless, straight weld and spiral weld, named for the way in which they are manufactured. Straight weld steel pipe is made by taking a flat sheet of steel and welding the ends together, resulting in a pipe with a single, straight seam down its length. Similarly, spiral weld pipe is also created by taking a flat sheet of steel and welding the ends together, except that the coil is wound at an angle, so the weld around the outside of the pipe runs in the shape of a helix rather than in a straight line. Unlike straight and spiral weld steel pipe, seamless steel pipe is made by stretching steel out into a seamless tube, and therefore the pipe has no seam.
Generally, welded pipe is considered weaker because of its seam, while seamless pipe lacks a weld and is generally considered safer. Seamless pipe is a top choice for high-pressure, high-temperature applications, such as those in oil and gas, power generation and the pharmaceutical industry. The downside of seamless steel pipe is that the rolling and stretching manufacturing process produces an inconsistent wall thickness compared to welded pipe, and it’s also more expensive to buy. Welded pipe is cheaper than seamless pipe and is typically good for lightweight applications such as transporting gas, electrical conduit and plumbing.
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