Sunday, January 21, 2018

Pipe & Tube

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.