Tube – What Is Piping: All about Piping Engineering

What is a Pipe? Pipes are used for transporting fluids and gases in Chemical, Petrochemical, Power Plants, Refineries, Storage units, compressed air systems, plumbing systems, etc. They are circular in cross-section and specified by Nominal Pipe Size. What is a Tube? Tubes are used for mechanical applications (Heat Exchanger, Fired heater, Boiler, etc.), for instrumentation systems (used for measuring instruments); for structural applications, etc and could be rigid or flexible. They are specified by their outer diameter and tube wall thickness, in inches or in millimeters. Differences between Pipe and Tube From a layman's viewpoint, Both Pipe and Tube seem to be the same as they have many similarities like both are hollow, made from metals, both can transfer fluids, etc. Many a time, these terms are used interchangeably. But in actual practice Tubes and Pipes are not the same as both possess different features. Through this article, we will try to investigate all such characteristics based on a few parameters like Size, Shape, Diameter, Thickness, Use, Availability, End Connection, Design Standard, etc. Sr NoParameterPipe CharacteristicsTube Characteristics1ShapeAlways cylindrical or round in shapeIn general, cylindrical. However, different other shapes like square, rectangular, etc. are available.2SizePipe is Specified by Nominal Pipe Size (NPS) or Nominal Bore (NB).The size of Tubes are specified in millimeter or in inches by outside diameter.3DiameterThe outside diameter of pipe up to size 12” are numerically larger than corresponding pipe sizeOutside diameter of tubes is numerically equal to the corresponding size.4ThicknessPipe Wall thickness is expressed in schedule number that can be converted into mm or inches.Tube Wall thickness is expressed in millimeter, or inches, or BWG (Birmingham wire gauge.)5Thickness IncrementPipe thickness depends on the schedule, so there is no fixed incrementThe thickness of tubes increases in standard increments such as 1 mm or 2 mm Difference Between Pipe and Tube Sr NoParameterPipe CharacteristicsTube Characteristics6ApplicationUsed in all Process, Power & Utility lines to carry fluids.Generally used in tracing lines, tubes for heat exchanger & fired heater & in instrument connection. They are more prevalent in medical area, construction, structural or load bearing.7AvailabilityAvailable as the small bore and the big boreNormally small-bore tube is used in process piping. For structural use, tubes are available in custom sizes.8Structural RigidityAlways rigid and resistant to bendingAvailable as rigid as well as flexible depending on the application. Rigid tubes are normally used in structural applications whereas copper and brass tubes can be flexible.9Joining and StabilityJoining pipes is more labour intensive as it requires flanges, welding, threading, etc.Tubes can be joined quickly and easily with flaring, brazing or couplings, but for this reason, they don’t offer the same stability10TolerancePipe tolerances are not too restrictive.Tolerances are very strict with tubes compared to pipes and tubes are often more expensive to produce than pipes Pipes used in operating process plant Sr NoParameterPipe CharacteristicsTube Characteristics11ManufacturingPipe manufacturing is easier as compared to tubesTubes need cumbersome tests, inspection and quality control than pipes.12CostCheaperCostlier13Packing & DeliveryDelivered in bundle as bulk item. Delivery time is short.Tubes are usually wrapped with wooden box or thin film and delivered with much care. Delivery time is longer.14Production QuantityProduced in mass quantity and for long distance applications.Produced in small quantity depending on requirement. Tubes used inside a Fired Heater Sr NoParametersPipe CharacteristicsTube Characteristics15End ConnectionNormally plain or bevelled for welding purposesWith coupling ends, irregular ends, special screw thread etc.16Surface FinishInner and Outer surface is rough with comparison to tubeNormally, both inner and outer surface are smooth17Common materialCarbon SteelAlloy Steel18Design Codes & StandardsThickness is decided as per governing codes like ASME B 31.3/ B31.1/ B 31.4/ B31.8 or IBR CodesDepending on use thickness is decided. I am sure there will be many more differences, I invite the readers to list out those in the comments section. Few more useful resources for you.Difference between Tee and Barred TeeComparison between Piping and Pipeline EngineeringDifference between Stub-in and Stub-on Piping ConnectionDifference between Centrifugal and Reciprocating CompressorDifferences between Hot-dipped galvanization and Electro-galvanizationCAESAR II vs START-PROF Piping Stress Analysis Software ComparisonAPI vs ANSI Pump