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Pipe vs Tube – What’s the Difference
Most have heard these two terms and yet few truly know the difference. Though the words pipe and tube (or tubing) are used interchangeably, they have very unique differences.
Generally speaking, tube refers to hollow sections, whether square, rectangle, round or oval, used primarily in structural applications. Or where a precise outside diameter (OD), such as medical equipment is required.
Piping on the other hand is used primarily in the transport or conveyance of gases or fluids. An application where flow, a measure of capacity is the most important metric to determine capacity. With pipe, there’s less of an emphasis on OD.
When talking about pipe or tube size, there are two measurements, OD and wall thickness (also referred to as gauge) and pipe schedule.
Outside Diameter (OD)
Tube requires an exact OD. As a result, both its measured and stated OD are within a very tight tolerance.
The OD for pipe is a nominal pipe size (NPS), whose measured and stated OD will have greater variation than tube.
Wall Thickness & Pipe Schedule
Both terms are measures of the difference between OD and ID (inside diameter), but they are not interchangeable.
Wall thickness is a reference for tube, measured in inches or by standard gauge (7 the heaviest, 22 the lightest). Pipe schedule is a term used for pipe.
For additional information, please see our pipe schedule chart.
Generally, tube is more expensive than pipe due to the higher manufacturing requirements needed to ensure a more precise OD as compared to a nominal OD for pipe.
How to Order
Tube is typically ordered by OD and wall thickness. Though you can order by (1) OD and ID or (2) ID and wall thickness.
Tube vs. Pipe
Tube is normally used for structural purposes and sizing is based on the exact outside diameter and wall thickness of the tubing.
Pipe is normally used to transport gases or fluids and sizing is based on the nominal outside diameter (NPS) and wall thickness.
NPS Nominal Pipe Size
Many believe that NPS refers to the ID on smaller pipes because of how the standard was originally defined.
The NPS OD was originally defined so that a pipe with a standardized OD and wall thickness typical of the period, would have a pipe ID that was approximately equal to the nomimanl size of the pipe.
For example, a 3" schedule 40 NPS has an outside diameter and wall thickness that roughly gives in an indisde diamater of 3".
Regardless of Wall Thickness
The Nominal OD of a Pipe Will Not Change