Pipe Vs
Tube
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Let us enter into the Topic.
We are going to compare the pipes and tubes that
are used in the Oil & Gas and Shipbuilding industries:
Let us know what are pipes and tubes?
A pipe is usually a hollow
cylinder of circular cross-section, used mainly to convey substances which can
flow such as liquids and gases (fluids), powders, slurry, and masses of small
solids.
Whereas pipe is a round
cross-section, tubes can come in different shapes such as square, rectangular
and cylindrical cross-section, which is also used mainly to convey substances
which can flow such as liquids and gases (fluids), powders, slurry and masses
of small solids.
Let us compare the engineering
aspects of the circular cross-sections:
Size:
# The pipe size is generally specified by a nominal diameter or nominal bore.
# The tube size is specified by its OD.
Wall Thickness:
# The pipes wall thickness is defined by schedule number.
# The tubes wall thickness is measured in millimeters or inches.
Outside Diameter:
# The OD of the pipe up to size 12” are numerically larger than corresponding pipe size
# The OD of the tube is numerically equal to the corresponding size.
Selection:
# In oil and gas or shipbuilding industries, the selection of the pipe depends upon the ID because it varies for each Schedule.
# In oil and gas or shipbuilding industries, the selection of the tube can go with its OD due to its thinner wall thickness.
From the below table, we are going to see some
major differences between pipe and tube:
|
Pipe
Verses Tube
|
Pipe
|
Tube
|
|
|
1
|
Key Dimensions (Pipe and Tube Size
Chart)
|
The most important dimension for a
pipe is the inside diameter (ID), expressed in NPS (nominal pipe size) or DN
(nominal diameter), which defines its fluid conveyance capacity. The NPS does
not match with its inside diameter, it is a rough measurement.
|
The most important dimensions for a
tube are the outside diameter (OD) and the wall thickness (WT). These
parameters are expressed in inches or millimeters and the OD of the tube is
numerically equal to the corresponding size.
|
|
2
|
Wall Thickness
|
The thickness of a pipe is designated
with a “Schedule” value (the most common are Sch. 40, Sch. 80 and Sch. 160).
Two pipes of different NPS and same schedule have different wall thicknesses
in inches or millimeters.
|
The wall thickness of a tube is
expressed in inches or millimeters. For tubing, the wall thickness is
measured also with a wire gauge nomenclature (Birmingham Wire Gauge, Stubs Iron Wire Gauge).
|
|
3
|
Cross Section of Pipes and Tubes
|
Circular in Cross-Sections.
|
Circular, rectangular, square and
oval in Cross-Sections.
|
|
4
|
Production range
|
Extensive (up to 80 inches and
above).
|
A narrower range for tubing (up to
5 inches), larger for steel tubes for mechanical applications.
|
|
5
|
Tolerances (straightness, dimensions,
roundness, etc) and Pipe verses Tube strength
|
Tolerances are set, but rather
loose. Strength is not the major concern.
|
Tubes are produced to very strict
tolerances. Tubes undergo several dimensional quality checks, such as
straightness, roundness, wall thickness, surface, during the manufacturing
process. Mechanical strength is a major concern for tubes.
|
|
6
|
Production Process
|
Pipes are generally made to stock
with highly automated and efficient processes, i.e. pipe mills produce
continuously and feed distributors stock around the world.
|
The tubing requires many more
production operations to make a finished product. It is normally of a lot
higher quality than the pipe, resulting in increased testing and inspections.
Pipe production far outweighs tubing production.
|
|
7
|
Delivery time
|
Can be deliverable in short period.
|
In common, delivery takes a long
period from the date of order placed.
|
|
8
|
Market price
|
Relatively lower price per ton than
the tubes.
|
Higher due to lower mills
productivity per hour, and due to the stricter requirements in terms of
tolerances and inspections.
|
|
9
|
Materials
|
A wide range of materials is
available.
|
Tubing is available in carbon steel,
low-alloy steel, stainless steel, and nickel-alloys and Steel tubes for
mechanical applications are mostly of carbon steel.
|
|
10
|
End Connections
|
Pipes are typically connected by
threading the ends and screwing together with couplings, T’s, or elbows.
Another common way of connecting pipes is welding them together or to other
components, such as flanges.
|
Tubes can be connected by flaring,
brazing, tube couplings, or welding.
Pressures within the tube normally dictate the type of coupling used.
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