What are the differences between steel pipe and tube?

Tube and pipe are terms often used interchangeably. To most people it doesn’t matter what the difference is, if any. After all, they are just hollow cylinders – right?

There are notable differences between tubing and piping – both in how they are made and in how they are used. And it does matter.

Let’s explore that.

Essentially, the main differences between steel pipe and tube is their application.

Tubing is generally a used for structural purposes. They are usually seam-welded, and their main feature is their strength. (Some tubes are used to transport fluids despite their seam welds, but these undergo significant pressure testing to ensure their integrity.)

When determining either tubing or pipe size, three main measurements are taken into consideration. These are:

  • Outside Diameter (OD)
  • Inside Diameter (ID)
  • Wall Thickness (WT)

Once you understand the application of each, a pipe or a tube can be specified by supplying two of these numbers. They are related by a simple equation: OD = ID + 2 * WT

Because the strength of a steel tube depends largely on the thickness of the wall, the OD and the WT are the most important numbers. Steel tubes come in square and rectangular tubes formed from their original round “mother tube”. Generally speaking, a tube will have a consistent OD and its ID will change.

Pipes are not usually used in the structure of a building, but are mainly utilised in transporting gases or fluids. These would include natural gas, heating oil, water, etc. They are usually a single, seamless product and categorised as vessels. Because of their general use, it’s important to know a pipe’s inside diameter – or its capacity. It is common practise to specify a pipe by using a Nominal Pipe Size (ANSI) or Diameter Nominal (ISO).

We at Steelmor offer a wide range of steel pipes, steel tubes, plates and sheeting. Why not visit our website at www.steelmor.co.za or call one of our friendly team on (011) 747 5700 to find out how we can assist you.