What is the Difference between Pipes and Tubes?

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What is the Difference between Pipes and Tubes?

One of the foremost frequent questions we have in our mind is “Pipe and tube is the same or different”? Although pipes and tubes may look similar the fact is they are quite different in nomenclature and sizing, so we discussed the difference between pipes and tubes in this post.

The terms Pipe and Tube are almost interchangeable, although minor differences exist — generally, a tube has tighter engineering requirements than a pipe. Both pipe and tube imply A level of rigidity and permanence, whereas a hose is typically portable and versatile. A tube and pipe could also be specified by standard pipe size designations, e.g., nominal pipe size, or by nominal outside or inside diameter and/or wall thickness. Also, there is a difference between the actual dimensions of the pipe and nominal dimensions of the pipe which is: A 1-inch pipe will not measure 1 inch in outside or inside diameter, Also there are many types of tubing are specified by actual inside diameter (I.D), outside diameter (O.D), or wall thickness.

We will now see some basics of Pipes and Tubes and then we will move to actual difference between pipes and tubes.

What is Pipe?

The pipe is a pressure-tight circular hollow section that used in piping systems to transport gases or fluids.

The most important dimension for a pipe is the outer diameter (OD) together with the wall thickness (WT). OD minus 2 times WT (schedule) determines the inside diameter (ID) of a pipe, which determines the liquid capacity of the pipe.

Examples of actual O.D. and I.D.

Actual outside diameters

  • NPS 1 actual Outer Diameter = 1.5/16″ (33.4 mm)
  • NPS 2 actual Outer Diameter = 2.3/8″ (60.3 mm)
  • NPS 3 actual Outer Diameter = 3½” (88.9 mm)
  • NPS 4 actual Outer Diameter = 4½” (114.3 mm)
  • NPS 12 actual Outer Diameter. = 12¾” (323.9 mm)
  • NPS 14 actual Outer Diameter = 14″ (355.6 mm)

Actual inside diameters of a 1 inch pipe.

  • NPS 1-SCH 40 = Outer Diameter 33,4 mm – WT. 3,38 mm – Inner Diameter 26,64 mm
  • NPS 1-SCH 80 = Outer Diameter ,4 mm – WT. 4,55 mm – Inner Diameter 24,30 mm
  • NPS 1-SCH 160 = Outer Diameter 33,4 mm – WT. 6,35 mm – Inner Diameter 20,70 mm

Such as above defined, the inside diameter is determined by the outside diameter (OD) and wall thickness (WT). The most important mechanical parameters for pipes are the pressure rating, the yield strength, and the ductility.

The standard combinations of pipe Nominal Pipe Size and Wall Thickness (schedule) are covered by the ASME B36.10 and ASME B36.19 specifications (respectively, carbon and alloy pipes, and stainless steel pipes).

  • For pipe sizes less than Nominal Pipe Size (NPS)14 inch (DN 350), both methods give a nominal value for the Outer Dia. that is rounded off and is not the same as the actual Outer Dia. For example, NPS 2 inch and DN 50 are the same pipes, but the actual Outer Dia. is 2.375 inches or 60.33 millimeters. The only thanks to obtaining the particular Outer Dia. is to seem it up during a reference table.
  • For pipe sizes of Nominal Pipe Size (NPS) 14 inch (DN 350) and greater the NPS size is the actual diameter in inches and the DN size is equal to NPS times 25 (not 25.4) rounded to a convenient multiple of fifty. For example, NPS 14 has an Outer Dia. of 14 inches or 355.60 millimeters and is equivalent to DN 350.

Use of Pipes :

  1. Process Pipings
  2. Process Equipment Manufacturing.
  3. Plumbing
  4. Tap water
  5. Irrigation
  6. Pipelines for transportation of gas or liquid over long distances
  7. Compressed air systems
  8. Pipe bombs
  9. Casing for concrete pilings used in construction projects
  10. High-temperature or high-pressure manufacturing processes
  11. The petroleum industry
  12. Oil well casing
  13. Oil refinery equipment
  14. Delivery of fluids, either gaseous or liquid, during a process plant from one point to a different point within the process
  15. Delivery of bulk solids, during a food or process plant from one point to a different point within the process
  16. The development of high storage vessels (note that enormous pressure vessels are constructed from the plate, not pipe due to their wall thickness and size).

Additionally, a pipe is employed for several purposes that don’t involve conveying fluid. Handrails, scaffolding, and support structures are often constructed from a structural pipe, especially in an industrial environment.

Manufacturing of pipes :

There are three processes for metallic pipe manufacture. Centrifugal casting of hot alloyed metal is one of the foremost prominent processes. Ductile iron pipes are generally manufactured as like that. Seamless (SMLS) pipe is made by drawing a solid billet over a piercing rod to make the hollow shell. As the manufacturing process doesn’t include any welding, seamless pipes are seemed to be stronger and more reliable. Historically, a seamless pipe was considered withstanding pressure better than other types and was often more available than welded pipe.

Progressive since the time of 1970 in materials, process control, and non-destructive testing allow the correctly specified welded pipe to replace seamlessly in many uses & applications. Welded pipe is made by rolling plate and welding the seam (usually by electrical resistance welding (“ERW”), or Electric Fusion Welding (“EFW”)). The weld flash is often faraway from both inner and outer surfaces employing a scarfing blade. The weld zone also can be heat-treated to form the seam less visible. Welded pipe often have tighter dimensional tolerances than the seamless type, and maybe cheaper to manufacture.

There are several processes that may be used to produce ERW pipes. Each of those processes results in the coalescence or merging of steel components into pipes. Electric current is skilled the surfaces that need to be welded together; because the components being welded together resist the electrical current, heat is generated which forms the weld. Pools of molten metal are formed where the 2 surfaces are connected as a robust current is skilled the metal; these pools of molten metal form the weld that binds the two abutted components.

Electric Resistance Weld pipes are manufactured from the longitudinal welding of steel. The welding process for ERW pipes is continuous, as against the welding of distinct sections at intervals. ERW process uses steel coil as feedstock.

The High-Frequency Induction Technology (HFI) welding process is employed for manufacturing ERW pipes. In this process, the present to weld the pipe is applied by means of a coil around the tube. High-Frequency Induction Technology (HFI) is usually considered to be technical “admirable quality” to “ordinary ordinary” ERW when manufacturing pipes for critical applications, like for usage within the energy sector, additionally to other uses inline pipe applications, also as for casing and tubing.

Large-diameter pipe (25 centimeters (10 in) or greater) could also be ERW, EFW, or Submerged Arc Welded (“SAW”) pipe. There are two technologies which will be wont to manufacture steel pipes of sizes larger than the steel pipes which will be produced by seamless and ERW processes. The two sorts of pipes produced through these technologies are longitudinal-submerged arc-welded (LSAW) and spiral-submerged arc-welded (SSAW) pipes. LSAW is made by bending and welding wide steel plates and most ordinarily utilized in oil and gas industry applications. Due to their high cost, LSAW pipes are seldom utilized in lower value non-energy applications like water pipelines. SSAW pipes are produced by spiral (helicoidal) welding of steel coil and have a price advantage over LSAW pipes because the process uses coils instead of steel plates. As such, in applications where spiral-weld is suitable, SSAW pipes could also be preferred over LSAW pipes. Both LSAW pipes and SSAW pipes compete against ERW pipes and seamless pipes within the diameter ranges of 16”-24”. Tubing for flow, either metal or plastic, is usually extruded.

The material of Construction for Pipes :

A pipe is formed out of many sorts of material including ceramic, glass, fiberglass, many metals, concrete, and plastic.

Typically, metallic piping is formed of steel or iron, like unfinished, black (lacquer) steel, steel, chrome steel, galvanized steel, brass, and ductile iron. Iron-based piping is subject to corrosion if used within a highly oxygenated water stream. Aluminum pipe or tubing could also be utilized where iron is incompatible with the service fluid or where weight may be a concern; aluminum is additionally used for warmth transfer tubing such as in refrigerant systems. Copper tubing is popular for domestic water (potable) plumbing systems; copper could also be used where heat transfer is desirable (i.e. radiators or heat exchangers). Inconel, chrome-moly, and titanium steel alloys are utilized in heat and pressure piping in process and power facilities. When specifying alloys for new processes, the known issues of creep and sensitization effect must be considered.

Lead piping remains found in old domestic and other water distribution systems but is not any longer permitted for brand spanking new potable water piping installations thanks to its toxicity. Many of the building codes now require the lead piping in residential or institutional installations which will be replaced with non-toxic piping or that the tubes’ interiors be treated with orthophosphoric acid. According to a senior researcher and lead expert with the Canadian Environmental Law Association, “…there is no safe level of lead [for human exposure]”. In 1991 the US EPA issued the Lead and Copper Rule, it’s a federal regulation that limits the concentration of lead and copper allowed publicly beverage, as well as the permissible amount of pipe corrosion occurring thanks to the water itself. In the US it’s estimated that 6.5 million lead service lines (pipes that connect water mains to home plumbing) installed before the 1930s are still in use.

Plastic tubing is widely used for its lightweight, chemical resistance, non-corrosive properties, and simply making connections. Plastic materials include polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), fiber-reinforced plastic (FRP), reinforced polymer mortar (RPMP), polypropylene (PP), polyethylene (PE), cross-linked high-density polyethylene (PEX), polybutylene (PB), and acrylonitrile butadiene styrene (ABS), for example. In many countries, PVC pipes account for many pipe materials utilized in buried municipal applications for beverage distribution and wastewater mains. Market researchers are forecasting total global revenues of more than US$80 billion in 2019. In Europe, the market value will amount to approx. €12.7 billion in 2020.

The pipe could also be made up of concrete or ceramic, usually for low-pressure applications like gravity flow or drainage. Pipes for sewage are still predominantly made up of concrete or vitrified clay. Reinforced concrete is often used for large-diameter concrete pipes. This pipe material is often utilized in many sorts of construction and is usually utilized in the gravity-flow transport of stormwater. Normally, such pipe having a receiving bell or a stepped fitting, with various sealing methods applied at installation.

Traceability and positive material identification (PMI):

When the alloys for piping are forged, metallurgical tests are performed to work out the material composition accidentally of every element within the piping, and therefore the results are recorded in a Material Test Report (MTR). These tests can be used to prove that the alloy conforms to various specifications (e.g. 316 SS, 304 SS). The tests are stamped by the mill’s QA/QC department and can be used to trace the material back to the mill by future users, such as piping and fitting manufacturers. Maintaining the traceability between the alloy material and associated MTR is a crucial quality assurance issue. QA often requires the warmth number to be written on the pipe. Precautions must also be taken to prevent the introduction of counterfeit materials. As a backup or a guaranty which avoids problems in future regarding etching/labeling of the material identification on the pipe, Positive Material Identification is performed employing a handheld device; the device scans the pipe material using an emitted electromagnetic radiation (x-ray fluorescence/XRF) and receives a reply that’s spectrographically analyzed.

What is Tube?

The meaning of TUBE is to be round, square, rectangular, and oval hollow sections that are used for pressure equipment, for mechanical applications, and for instrumentation systems. In oil and gas industries, tubes are not just used as a structural part but also used in the heat exchanger and fired heater for a process application.

Tubes are indicated with an outer diameter and wall thickness, in inches or in millimeters.

Tubes are typically ordered to outside diameter and wall thickness; however, it’s going to even be ordered as OD & ID or ID and Wall Thickness. The strength of a tube depends on the wall thickness of the tube. To define the thickness of the tube gauge number is used. Smaller gauge numbers indicate larger outside diameters. The inside diameter (ID) is theoretical. Tubes can are available different shapes like square, rectangular, and cylindrical, whereas Pipe is usually round. The circular shape of the pipe makes the pressure force evenly distributed. Pipes accommodate larger applications with sizes that range from a ½ inch to several feet. Tubing is usually utilized in applications where smaller diameters are required

Tubing is manufactured in three classes: seamless, as-welded, or electric resistant welded (ERW) and drawn-over-mandrel (DOM).

  • Production of seamless tubing done by extrusion or rotary piercing.
  • Drawn-over-mandrel (DOM) tubing is produced by a cold-drawn electrical-resistance-welded tube that’s drawn through a die and over a mandrel to make such characteristics as dependable weld integrity, dimensional accuracy, and an excellent surface finish.

There is a lot of industry and government standards for pipe and tubing. Many standards exist for tube manufacture; a number of the foremost common are as follows:

  • American Society for Testing and Materials ASTM A213 Standard Specification for Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, Heat-Exchanger Tubes.
  • American Society for Testing and Materials ASTM A269 Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Service
  • American Society for Testing and Materials ASTM A270 Standard Specification for Seamless and Welded Austenitic Stainless Steel Sanitary Tubing
  • American Society for Testing and Materials ASTM A511 Standard Specification for Seamless Stainless Steel Mechanical Tubing
  • American Society for Testing and Materials ASTM A513 is the Standard Specification for Electric Resistance Welded Carbon and Alloy Steel Mechanical Tubing
  • American Society for Testing and Materials ASTM A554 Standard Specification for Welded Stainless Steel Mechanical Tubing
  • British Standard BS 1387:1985 are the standards for the specification of screwed and socketed steel tubes and tubular and for plain end steel tubes suitable for welding or for screwing to BS 21 pipe threads

American Society for Testing and Materials (ASTM) material specifications generally cover a spread of grades or types that indicate a selected material composition. Some of the most commonly used are:

  • TP 304
  • TP 316
  • MT 304
  • MT 403
  • MT 506

In installations using hydrogen, copper and chrome steel tubing must be factory pre-cleaned (ASTM B 280) and/or certified as instrument grade. This is because of hydrogen’s propensities: to explode within the presence of oxygen, oxygenation sources, or contaminants; to leak because of its atomic size; and to cause embrittlement of metals, particularly under pressure.

Strength Calculation for Tube :

For a tube of silicone rubber with a tensile strength of 10 MPa and an 8 mm outside diameter and 2 mm thick walls. The maximum pressure may be calculated as follows:

Outside diameter = 8 millimetres (0.3150 in)

Wall thickness = 2 millimeters (0.07874 in)

Tensile strength = 10 * 1000000 [Pa]

Bursting Pressure (BP) = (Tensile strength * Wall thickness * 2 / (10 * Outside diameter) ) * 10 [Pascal]

Gives bursting pressure of 5 MPa.

Using a safety factor:

Pressure max (P max.)= (Tensile strength * Wall thickness * 2 / (10 * Outer diameter)) * 10 / factor of safety [Pascal]

The Difference Between Pipes and Tubes :

The difference between pipes and tubes can be briefly done by considering some pipes and tubes parameters such as Shapes, Measurement or Dimensions, Wall Thickness, Production Range, Telescoping Abilities, Rigidity, Tolerances (straightness, dimensions, roundness, etc), Production Process, Delivery time, Applications, Metal Types, Size, Strength, End Connections, and Market Price.

Now we will summarize this pipes and tubes difference tabular form so that it helps you to understand in better way.

Sr.No.Parameters PipeTube
1.Shape:  Pipes are always round in shape.  Tubes can be square, oval, rectangular or round.  
2Measurement/Dimensions:  The most important dimension for a pipe is the outer diameter (OD) together with the wall thickness (WT). OD minus 2 times WT (SCHEDULE) determine the inside diameter (ID) of a pipe, which determines the liquid capacity of the pipe. The NPS does not match the true diameter, it is a rough indicationThe most important dimensions for a steel tube are the surface diameter (OD) and therefore the wall thickness (WT). These parameters are expressed in inches or millimeters and express truth dimensional value of the hollow section
3Wall Thickness:  The thickness of a steel pipe is designated with a “Schedule” value (the commonest are Sch. 40, Sch. STD., Sch. XS, Sch. XXS). Two pipes of different Nominal Pipe Size (NPS) and the same schedule have different wall thicknesses in inches or millimeters.The wall thickness of a steel tube is expressed in inches or millimeters. For tubing, the wall thickness is measured also with a gage nomenclature.
4Production Range:  Broad (up to 80 inches and above)A narrower range for tubing (up to 5 inches), larger for steel tubes for mechanical applications
5Telescoping Abilities  Pipe, on the opposite hand, doesn’t have a flash weld.  The tube can be telescoped. Attention towards the account for the flash weld inside the tube. DOM (Drawn over Mandrel) Tube is that the best material for telescoping because the within flash weld has been removed.
6Rigidity  Pipes, on the opposite hand, are invariably rigid and can’t be shaped without special equipment.Although copper and brass tubes are often shaped relatively easily, tubes are typically rigid.
7Tolerances (straightness, dimensions, roundness, etc)  Tolerances are set, but rather loose. Strength is not a major concern.Steel tubes are produced to very strict tolerances. Tubulars undergo several dimensional quality checks, such as straightness, roundness, wall thickness, surface, during the manufacturing process. Mechanical strength is a major concern for tubes.
8Production Process:  Pipes are usually made to stock with highly automated and efficient processes, i.e. pipe mills produce an endless basis and feed distributors stock round the world.Tubes manufacturing is lengthier and more laborious.
9Delivery time:  For pipe delivery time Can be short.  For tubes Generally longer  
10Applications:  Only pipes are pressurized (pressure rated) and considered to be used for the transference of fluids or gas.Tubes, on the opposite hand, are utilized in structural applications.
11Metal Types:  A wide range of materials is available e.g Stainless steel, Mild Steel, Copper, Brass, Bronze, Aluminium, Carbon Steel, Hot-rolled Steel, etc.Tubing is available in carbon steel, low alloy, stainless steel, and nickel-alloys; steel tubes for mechanical applications are mostly of carbon steel.
12Size:  Pipe is usually available in larger sizes than tubeTube having small sizes than pipe.
13Strength:  The Pipe is less strong than a tube.A Tube is stronger than the pipe.
14End Connections:  The most common are beveled, plain, and screwed ends. Mostly flange end or threaded connections are used.Threaded and grooved ends are available for quicker connections on site. Mostly Tri clover end (TC Type) connection is used.
15Market Price:  Pipes relatively lower price per ton than steel tubes.Higher due to lower mills productivity per hour, and due to the stricter requirements in terms of tolerances and inspections.

These are all differences between pipes and tubes done on the basis of the above parameters. This all about pipes and tubes difference we have explained in detail so that all your doubt concepts will clear and helps you to learn and enhance your knowledge.

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Imran Pinjara

Author of Book " Master in Fabrication Layout Development " Published worldwide. Founder and CEO of Let'sFab Educational Services. More than 8 Years of Professional Experience in Field of Pressure Vessel, Heat Ex changer, Storage Tanks, Piping and other Process Equipment Fabrication Industry. He had worked in many Fabrication Industry from small workshop to MNC Company. He had Completed PGDM in Process Piping Design and Engineering as per ASME B31.3 and Bachelor of Mechanical Engineering.