The Differences between Tubes and Pipes

The Differences between Tubes and Pipes

  • Jul 19, 2022
  • Hits: 4
The differences between T92 and P92
Tubes refer to small pipes, which are generally used as a superheater or a reheater in a boiler. Pipes are large tubes which are generally used in the main steam pipeline. Like tubes and pipes made of 92 steel, there is not difference in composition, but the process is different. The structure is not the same in the use. T92 is used to manufacture the superheater or reheater of thermal power station boilers. The outer surface of the tube is corroded by high temperature and flue gas produced by fuel combustion, and the inner surface is eroded by high temperature and high pressure steam. P92 is used to make steam pipes, which is mainly used to transport high temperature and high pressure steam, and is eroded by high temperature and high pressure steam. The composition control range of the two is the same, but the production process is different.
 
The differences between Tubes and Pipes
  Tubes Pipes
Sectional shapes Tubes have square, rectangular and round shapes. Pipes are round.
Toughness Tubes are rigid and there are also flexible tubes made of copper and brass. Pipes are rigid and resistant to bending.
Diameters Tubes are pipes with  small diameters, which are generally between 1/8 to 5/8 inches (=3~16mm)
 		 Pipes have a large diameter, which are generally between 15 to 1500mm (=1/2~60 inches). There are also pipes with diameters smaller or larger than this range, but they are hardly used.
Features of size standards Tubes use the outer diameter or OD to indicate the diameter specification. For example,
1/4’’ (6.25mm) OD tube means a tube with an outer diameter of 1/4 inches. The accuracy of the outer diameter is paid attention to, because the tube is connected by a ferrule, and the tube and pipe fittings with the same outer diameter can be connected by a ferrule.		 The nominal diameter DN is used for indicating the diameter of the pipe. DN50 means pipes with 2 inches, which can be expressed as Φ57×3.5mmΦ57×3.5mm or Φ60×3mmΦ60×3mm. Wall thickness is paid attention to for pipes, because pipes mainly convey fluids and high internal pressure capacity are required.
 
Names on the market  
The wall thickness is thinner for the tube, which is called the thin walled tube on the market. It is expressed by its actual thickness (inch or mm), and it is generally 1 to 2mm.		 The wall thickness of the pipe is standard.  From No.5 to Sch.No.XXS, different pipes with diameters or materials have their standard wall thickness series. Pipes have the same Sch.No. but different  diameters or materials, the actual wall thickness is not the same.
Connection methods The wall of the tube is thin, and it is not allowed to have threads on it. After annealing, it is connected by a ferrule. Pipe connection methods include flange connections, thread connections and welding connections. Flange connections are used for most situations, and the threaded connection is allowed for low pressure occasions.
Connection characteristics Tubes with the same OD can be connected with a ferrule, which is fast and can be disassembled for many times. The standard number of flanges and threads must be clearly noted, for example, 2''-ANSI-150-RF.
 
Bending The tube can be bent directly according to the requirements of the bending angle (no need to use pipe joints), which can reduce potential leakage points. Generally, elbow joints are used for connection when bending (elbow joints are generally threaded, and if you need to bend the pipe, the arched thread is required)
 
Installation A pipe with 6 meters can be cut freely according to the specific construction conditions on site. A pipe with 6 meters can be cut freely according to the specific construction conditions on site.
 
Applications Tubes are generally used for heat tracing and insulation of measuring pipelines and pneumatic signal pipelines in instrument systems and sample pipelines of online analyzers. Pipes are widely used in process pipelines and utility pipelines.
 
The connection requirements Dual ferrules and single ferrule must be able to be used. Pipes Can't be connected with dual ferrules or single ferrule.
 
Pipe characteristics The tubes are generally seamless stainless steel copper and brass pipes.  Seamless steel pipes and seam steel pipes are selected according to the application.
 
The steel pipe material standards of the United States and Japan clearly divide steel pipes into two types, namely pipes and tubes (the standard formula for calculating wall thickness is different). Pipe refers to a hollow pipe with a circular cross-section used for fluid transportation. Its specifications are expressed by the series of nominal diameter and wall thickness. For pipes with the same nominal diameter, the wall thickness can be different, but the outer diameter is the same. Pipes are the main pipes used in industrial pipelines. A pipe mainly has the function of transporting the pressurized medium from one place to another and doesn’t focus on the heat exchange function. For example, the main steam pipe, ascending and descending pipes or other pipes connected to tees, elbows and valves are pipes.

A tube is a general term for hollow tubes, which has round or other shapes. For a round tube, its specifications are determined by two of the outer diameter, inner diameter and wall thickness. A tube is often used in small diameter pipes with 5 inches or less such as instrument pipes, heat tracing pipes, hydraulic or pneumatic pipes in piping systems. A tube mainly focuses on internal and external heat conduction and heat exchange, such as superheater tubes, reheater tubes, gas-saving tubes and water wall tubes. Generally speaking, the unit price of the tube is higher than that of the pipe.
 
However, not all the diameters of pipeline components use nominal diameters, and not all pipelines adopt pipes. For example, high temperature and high pressure pipes and clean pipes are often expressed in the form of outer diameter x wall thickness.
 
In the ASTM and JIS steel pipe standard systems, there are obvious differences between pipes and tubes in terms of technical requirements and dimensional tolerances.

Next: Alloy Steel Pipes

Previous: Several Major Factors Affecting Sealing Performance of Flanges (Part Two)