What is Steel Pipe?

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  • Written By: B. Turner
  • Edited By: Bronwyn Harris
  • Last Modified Date: 02 October 2019
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Steel pipe is a building material made from an alloy of iron and carbon. It is widely used in the construction industry, but can also be found in a variety of manufacturing and industrial applications. In plumbing systems, steel pipe can be used to transport liquids and gases for commercial and residential buildings, as well as in municipal water supplies. This material also acts as a structural component for scaffolding and framing systems. Outside of the US, the term “tube” is often used instead of “pipe.”

There are several different types of steel pipe available for use in various applications. The most common is carbon pipe, which is so named because it contains no other alloys. Carbon pipe is widely available and relatively affordable, making it a popular choice for very large projects such as pipelines. Stainless steel pipe is made from an alloy of steel and chromium, and is one of the more expensive types of pipe on the market. It offers a high level of corrosion-resistance, which allows smaller and thinner pipes to be used, even in highly corrosive or acidic scenarios.


Galvanized steel is often used for pipes that will be exposed to harsh conditions like saltwater or marine use. This material features traditional carbon steel with an electroplated zinc coating, which helps resist rust and corrosion. When it comes to selecting pipe for most plumbing applications, black steel pipe is commonly used. The black coating is caused by oxidation of the pipe's surface during manufacturing, and is considered aesthetically pleasing for pipes that will be left exposed. These pipes are usually treated with an anti-corrosion sealer at the factory before they are sold.

Steel pipe is available in either seamless or welded versions. Seamless pipe is made using a piercing rod, which gives the material a smooth and even finish with no joints. This product is the more expensive of the two, but is also considered more reliable, especially in high pressure applications. Welded pipe is made from steel sheets that are rolled around a form, then welded shut along the joints. While welded steel pipe is less expensive, it is also more likely to fail, and can't generally hold up well in high pressure uses.

In the US, steel pipe is measured using a system known as Nominal Pipe Size (NPS). NPS provides the outside diameter of the pipe as well as the thickness of the pipe walls. For example, a pipe labeled NPS 14 Schedule 40 means that the pipe's outer diameter is 14 inches (35.56 cm), while its walls are .437 inches (1.11 cm). The value of a pipe's “Schedule” can be found using NPS tables, and the higher the schedule, the thicker the walls of the pipe will be. The European equivalent of NPS is known as Nominal Diameter (ND).


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