Pipe & Tube
To an
outsider, pipes and tubes may seem like they should be synonymous. To a process
engineer, the measurements, standards and language used to distinguish the two
couldn’t be more different. In fact, differences in nomenclature and measurements
could cause quite the headache if tubes and pipes were mistakenly assumed to be
interchangeable.
The main
Differences between Pipes and Tubes
1) Diameter: pipe diameter refers to nominal
pipe diameter (i.e. not actual) and we use pipe schedule to know the real
actual diameter, real diameter is always larger than nominal outside diameter
but for pipe sizes, NPS 14 and above Outside Diameter is same as NPS , pipes
usually used in applications that need large diameters.
Tubes diameter always refers to its actual OD
diameter, it is usually used in applications than need small diameter or know
OD diameter with no need to search for its OD diameter like H.E design.
1) Wall thickness: for a pipe we always use schedule
like 20, 40, and 80. While for tube we use “BWG” Birmingham Wire Gauge is also
known as Stubs' Wire Gauge used for drill rod and tool steel wire.
For example:
Diameter 8inch/219.1 pipe, pipe schedule is SCH
40 = wall thickness is 0.322inch/8.18mm,
Diameter 12 inch /323.9 pipes, sch 40 refers wall
thickness of 0.406inch/10.31mm.
1) Shape: Tubes can come in different shapes
like square, rectangular and cylindrical. Pipe is always cylindrical or round.
1)
Pipes Tolerance & Tube Tolerance: Pipes are usually used for transporting or distributing, then the
properties of pressure or straightness, roundness are strictly specified, the tolerance for pipes is looser than tubes comparatively. Here
the tolerance refers to diameter tolerance, wall thickness tolerance,
straightness tolerance, roundness tolerance etc.
2)
Manufacturing Difference of pipes and tubes: as we
mentioned above, tubes will require higher level requirements, consequently,
even from the material producing to the pipe or tube manufacturing process will
be different. Tubes will require much more process, tests, inspection than
pipes. The delivery time will be longer, too. The yields of tubes are
comparatively much lower than pipes. Pipe manufacturing is easier compare to
tubes and it’s in mass production.
3)
Cost & Price: as per to the above, to
manufacture tubes will take much more labor, energy, material etc., so the
production cost is surely higher than pipes. And just because the high level
requirement of tubes, the low yield of tubes will also increase the cost and
price. While the process of pipes is easier. And pipes are manufactured in
large lot and cut the cost.
4)
Use of Pipes and Tubes: Pipes
are used for fluids and gases, such as water, oil, gas
or propane or as steam pipe, boiler pipe etc. Just because of this, the outside
& inside diameter is the key measurement — it indicates how much can flow
through the pipe. Also that’s the reason why the pressure rating is so
important, because the pressure must be under the transport or distribute
pressure range. Tubes, however, are often put to use in applications that
require precise outside diameters, like with medical tubes, weapon part,
industrial parts, cooler tubes, heat ex-changer tubes and boiler tubes. Tubes
are usually used in medical area, construction, structure or load bearing etc.
This is why the outside diameter is important because it indicates how much it
can hold as a stability factor.
5)
Material: Piping is usually
made of carbon steel or low alloy steel. While tubing is often made of
mild steel, aluminum, brass, copper, chrome or stainless steel etc. Different materials
also lead to different cost and price.
6)
Mechanical Properties and Chemical Properties: For pipes the pressure rating, yield strength, ductility
properties are more important. However, for tubes, the hardness, tensile
strength, high precision is the key to high quality. Those elements like C, MN,
S, P, Si are the main chemical elements for pipes, and there is few micro elements
requirements. While for tubing, the micro-elements are very important to the
quality and process.
