what is the difference between tube and pipe in piping engineering?

Answer 1

Pipes:
Since the purpose with a pipe is the transport of fluids like water, oil and many other products, the most important pipe property is the capacity, or in reality, the inside diameter of the pipe. The nominal diameter of a pipe is therefore related to the inside diameter.

If we take a look at ASME/ANSI B 36.10 Welded and Seamless Wrought Steel Pipe, the inside diameter of a 2'' pipe schedule 40 is 2.067". The inside diameter of a schedule 80 pipe is 1.939". Both inside diameters are close to 2". The outside diameters for both schedules are 2.375".

Since the outside diameter of a single nominal pipe size is kept constant, the inside diameter of a pipe will depend on the "schedule", or the thickness, of the pipe. The schedule and the actual thickness of a pipe will vary with size of pipe.

It is common to identify pipes in inches by using NPS or "Nominal Pipe Size". The metric equivalent is called DN or "diametre nominel". The metric designations conform to International Standards Organization (ISO) usage and apply to all plumbing, natural gas, heating oil, and miscellaneous piping used in buildings. The use of NPS does not conform to American Standard pipe designations where the term NPS means "National Pipe Thread Straight".

Nominal Bore (NB) may be specified under British standards classifications along with schedule (wall thickness).

The tolerances are looser to pipes compared with tubes and they are often less expensive to produce.

Tubes:
The nominal dimensions of tubes are based on the outside diameter. If we look at Copper Tubes - ASTM B88 the outside diameter of a 2" pipe is 2.125", relatively close to 2".
The inside diameter of a tube will depend on the thickness of the tube. The thickness is often specified as a gauge. If we look at Copper Tubes - ASTM B88 the wall thickness of 0.083"of a 2" pipe is gauge 14.

The tolerances are higher with tubes compared to pipes. Tubes are often more expensive to produce than pipes.

The distinction between tube and pipe, based on wall thickness limit and/or wall to diameter ratio), is a little different from industry to industry. Tubing is considered as having a wall thickness of up to 1/4-in. or less and a diameter of 6-in or less, while pipe has a wall thickness above 1/4-in. and a diameter greater than 6-in. Having said this, the author has done development work for a stainless steel structural tubing producer at wall thicknesses up to 0.315-in., hence the rather blurred nature of the definition.

Answer 2

Hi Veeru, Pipe and Tube What is the difference between pipe and tube? At first glance, the naive might say "none". After all, they're both just hollow cylinders. That's wrong, of course. There is a difference (in the metalworking arena) For any hollow cylinder, there are three important dimensions - the outside diameter (od), the inside diameter (id) and the wall thickness (wt). Since these three are related by a simple equation: od = id + 2 * wt Tubing is more frequently used in structures so the od is the important number. Strength depends on the wall thickness. So tubing is specified by the od and the wt. Very logical and simple to measure. The id is simply whatever falls out of the equation above. Pipe is normally used to convey gases or fluids so the internal cross-sectional area (defined by the id) is important. It's therefore not surprising that pipe is specified by the id. Although anyone who's ever done any plumbing knows that the id on the pipe label is only a *nominal* id. While the designation for tubing is straightforward, that for piping is obscure for some perverse reason unclear to me. All pipe of a given nominal size has the *same od*. Good Luck.

Answer 3

The thickness of the walls.Also pipe and tube are delineated by inside and outside measurements

Answer 4

Tube = Plastic
Pipe = Metal