Pipe vs Tube vs Tubing Definitions Dimensions and Industrial Uses

Pipe and tube are virtually identical, but pipe is a product of nominal pipe size (NPS) for fluid conveyance applications while tube is a product of outside diameter (OD) and wall thickness for exact-fit mechanical, heat transfer and instrumentation applications. The two words are used interchangeably in everyday speech, and that’s where you’re going to make ordering errors. This guide also describes tubing, provides examples of real sizes in millimetres and inches and identifies the standards that are involved and where the products are used. If you need a quick answer skip to the comparison table or the dimension section.

Overview of Pipes vs Tubes

The table below sets out the difference between pipe and tube on the points that matter most when you write an enquiry.

What Is Pipe?

Pipe is a hollow round product used to convey fluids, gases, steam and slurries in piping systems. Its job is to move material from one point to another, so the bore matters as much as the outside. Pipe size is given by two labels. NPS is the inch based label used in North America and worldwide. DN (diameter nominal) is the metric label in millimetres, so NPS 2 matches DN 50. In India and the UK you will also see NB (nominal bore) used alongside DN and NPS. These are labels, not measurements. Wall thickness is given by a schedule number (SCH) such as SCH 10S, SCH 40, or SCH 80. Dimensions follow ASME B36.10M for carbon and alloy steel pipe and ASME B36.19M for stainless steel pipe. Process piping is commonly designed under ASME B31.3.A pipe is always round. It is joined by butt weld, socket weld, threaded or flanged connections, depending on size, pressure, and service.

What Is Tube?

Tube is a hollow product specified by its actual OD and wall thickness (WT), given in millimetres, inches or gauge. Tube is held to tighter dimensional control than pipe, which is why it suits parts that must fit precisely.Tube can be round, square, rectangular or oval. Many industrial tubes are round, and you will find them in heat exchangers, condensers, boilers, instrumentation lines and hygienic systems. It is a mistake to think tube is only structural. A large share of stainless steel and nickel alloy tube goes into fluid and heat transfer service. Round tube is the core format at Stellar Alloys, with selected square, rectangular, capillary and heat exchanger tube options by material. You can see the full pipes and tubes range on the website. Tube is usually joined with compression fittings, flare fittings or orbital welding. It can also be bent to route around obstacles, which reduces the number of joints in a line.

Pipe vs Tube Dimensions: How Size Is Defined

Wall thickness

Pipe wall is set by schedule. Tube wall is stated as an actual thickness in millimetres or inches, or as a gauge such as Birmingham Wire Gauge (BWG). Our pipe thickness chart lists schedule values by size.

Worked example: 2 inch pipe vs 2 inch tube

Take the same wall thickness in both cases, 2.77 mm (0.109 in). The inside diameter is the OD minus 2 x the wall thickness.

Both are called “2 inch”, yet the pipe is 9.5 mm larger in OD and its bore is about 9.5 mm larger too. The gap grows with size. NPS 4 pipe has a 114.3 mm OD, while a 4 inch tube has a 101.6 mm OD.

How to tell whether you have a pipe or a tube

1. Measure the OD with calipers or a tape.
2. Compare it with the NPS table above.
3. About 60.3 mm on a “2 inch” item means NPS 2 pipe.
4. 50.8 mm means 2 inch tube.

Pipe vs Tube vs Tubing: Standards That Define Each

Standards are how mills and buyers actually tell pipe and tube apart. Pipe standards follow NPS and schedule. Tube standards follow OD and wall, with tighter tolerances.

Tolerance, Strength and Pressure Rating: Is Pipe or Tube Stronger?

Tube is generally held to tighter OD and wall tolerances, and pipe to wider ones. Exact limits depend on the product standard and the general requirement standard that goes with it: ASTM A999 for alloy and stainless steel pipe and ASTM A1016 for alloy and stainless steel tubes. Always read the limits from those documents rather than from a general guide. Neither product is stronger by definition. Strength and pressure capacity depend on the material, the OD, the wall thickness and the temperature. A thick walled tube can hold more pressure than a thin walled pipe of the same alloy, and the reverse is also true. Both are designed for pressure by calculation under the governing code. The pipe thickness chart explains the method, and it shows why wall thickness is chosen for the duty and not by whether the product is called pipe or tube.

Seamless and Welded Pipe and Tube

A common belief is that seamless means pipe and welded means tube. That is not correct. Both pipe and tube are made seamless and welded, including electric resistance welded (ERW) and electric fusion welded (EFW) forms. The choice depends on size, pressure and cost. Seamless is often chosen for higher pressure and critical service, while welded is often chosen for larger sizes and cost control. Our guide to seamless vs welded steel pipe covers the trade offs.

Industrial Uses of Pipe vs Tube

How to choose between Pipes vs Tubes

A clear request avoids delays, and mixing pipe and tube terms is a common cause of wrong quotes. Use the checklist that matches your product.

 Stellar Alloys supplies with MTC (mill test certificate) and heat-number traceability, and can supply custom sizes and cut lengths, with export documents for overseas orders. See our mill test certificates and quality approvals and the global export guide for details, or request a quote with your specification.

Conclusion

The rule behind pipe vs tube is simple: pipe is ordered by NPS and schedule, tube is ordered by OD and wall, and tubing is tube supplied for a service or in long lengths. Once you know which size basis your drawing uses, the tube vs pipe question is easy to settle, and your RFQ will be accurate. Send your material, standard, size and quantity, and Stellar Alloys will quote against it. Request a quote today.