Pipe (technology)

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Round tube
PVC-U pressure pipe transparent

A tube (also: a tube ) is an elongated hollow body, the length of which is usually much greater than its diameter . In contrast to a hose , a tube is made of a relatively inflexible material.


Pipes generally have a circular cross-section, which is the optimal design for the most common applications. Pipes intended to be used as a beam or rod are also made with rectangular, oval and other cross-sections. They are then more resilient in one direction ( strength ) and also have less deformation ( stiffness ).

Pipes are used for the following functions:

If you bend a straight pipe with the help of a pipe bending device, a pipe bend is created .

The area of ​​application of a pipe is determined by its properties such as cross-section, material, surface quality, diameter (DN) and pressure rating (PN) .

Materials and manufacture

Pipe storage in a petroleum refinery
Spiral duct chimney

Pipes are made from a wide variety of materials and are not flexible or not very flexible (in contrast to hoses ).

The following metallic materials are used:

Metal pipes are now made either with a welded seam or seamless. The winding of a sheet metal strip into a tube ( spiral-seam tube ) is particularly common in the ventilation sector.

Furthermore, pipes are also made of non-metallic materials:

According to Harald Roscher, supply and disposal lines can be divided into pipe generations, which relate to the main operating times of different material generations. For example, gray cast iron of the "1st generation" has not been used since 1930, whereas spheroidal graphite cast iron is still used today. The use of polyethylene began in the 1950s, with PE 100 ("3rd generation) not being used until 1995.

Since pipes and their connections are the largest investment by utility and disposal companies, great efforts are made to determine the ideal time for rehabilitation. For this purpose, on the one hand, the pipe generations with their manufacturing and material specifics and, on the other hand, a material-technical condition analysis can be used to determine the remaining useful life of the pipe. A failure of the pipe in the operating state would only allow the failure-related maintenance (so-called fire brigade strategy) as a renovation strategy and is usually associated with higher and above all unplanned costs.

Metal pipes


Pipes with a small wall thickness in relation to their outer diameter are i. d. Usually manufactured as welded tubes. First, a hollow body is produced by bending or rolling sheet metal , which is then welded to the joints. Pipes up to a meter in diameter can be welded lengthways, larger pipes are spiral seam welded as spiral tubes and large pipes made of heavy plate are bent and welded in pieces.


  • Pipes up to a diameter of about 200 mm with large wall thicknesses are usually produced seamlessly. The process most commonly used to date (for non-ferrous metals) is based on the fact that a glowing starting piece - called a block or bolt - made of brass, copper, steel etc. is pressed using a hydraulic press through a ring-shaped tool called a die ( extrusion ). Copper and steel pipes must be rapidly cooled in water immediately afterwards. The length of the pressed pipes is usually less than 50 m. The tube is wavy and soft, slightly flexible, its dimensions are imprecise.
  • Newer methods of manufacturing seamless tubes aim to continuously manufacture tubes that are as long as possible. The processes used have already been used in a similar form in wire production, with a non-ferrous tube first being formed by continuous casting , which is then reduced in diameter by rolling.
  • Since tubes are rotationally symmetrical components, they can also be manufactured using the centrifugal casting process. Cast iron pipes are often given a coating of epoxy resin ( SML pipe ) or zinc or a cement mortar lining.
  • Seamless tubes can also be made by plastic forming, e.g. B. skew rolling , plug rolling , stretch reduction , push bench method or especially in the pilgrim step method .

The Mannesmann brothers received the patent for the first process for manufacturing seamless steel tubes in 1885 .

In further process steps, the pipes are often further processed by drawing in order to achieve certain diameters, wall thicknesses, material strengths and surface qualities.

  • A pipe can also be produced from solid material by deep drilling , e.g. B. wooden pipes, or today steel pipes for special high pressure applications. Steel pipes are then not pulled. Any concentricity errors can be compensated by turning the outer wall over.

Pipes as semi-finished products are sometimes z. B. processed by grinding , honing , rubbing , roller burnishing, the latter especially for steel pipes. Finished pipes are cut into standard lengths (e.g. 6 m). Pipes with small diameters are usually sold in so-called “coils”.

Plastic pipes

Plastic pipes are important in areas such as sewage disposal, drinking water and gas supply, cable protection, and agriculture and industry. Advantages over materials such as aluminum, concrete, cast iron, copper and steel are its low weight, resistance to corrosion and chemicals and ease of use. Seamless pipes are created by extrusion . They can be connected using various techniques ; clamping, compression and welding connections are the rule. Certain materials such as PVC can also be glued.

Polyethylene pipes made of HD-PE or PE 100 are widespread for the distribution of drinking water and gas, especially outside buildings in the ground. Tube of PE-X can be used for heating installations as a hot-water line, and. However, without further measures, PE-X is not oxygen-tight.

Pipes made of PP or PP-R have long been used for installations in building technology and are connected by heating element socket welding . Even the butt welding ( butt welding ) and electro fusion welding is possible.

Chemical-resistant pipe systems made of ABS and PVC are used in industry. PVC-U pipes are often used in pressure ratings PN 10 and PN 16 and are also offered as transparent pipes. Pipes made of PVC-C can (in contrast to PVC-U) also be used as hot water pipes. These pipes were also used in building installations under the trade names TC Quickpipe (gray) and Friatherm (yellowish), from 1990 with the uniform outer diameters of 16, 20, 25, 32, 40, 50, 63, 75 and 90 mm. The systems were withdrawn as leaks occurred at the adhesive points after a few years with permanently increased water temperatures under some operating conditions. The manufacturer of the Friatherm pipes also allows their fittings to be used with Quickpipe pipes, which can be helpful in the event of repairs.

Wastewater pipes are made in particular from PE, PP and PVC and, for special applications, from GRP .

The largest manufacturers in Europe are Aliaxis , Aquatherm , Wavin , Uponor , Pipelife ( Wienerberger ), Geberit , Alphacan , Fränkische Rohrwerke , DYKA , Polypipe , Rehau and Uralita .

Glass tubes

Glass tubes (e.g. borosilicate glass tube) are also used for a wide variety of uses in the field of conveying liquids and gases. Due to their high corrosion resistance , glass tubes are preferred over other materials for certain applications. Glass is an established material, for example for waste water pipes in laboratories or as a heat exchanger in corrosive environments.


The connections are screwed, soft or hard soldered , welded , glued , pushed into one another with a seal , clamped with a clamping ring , just plugged in or pressed. There are also compression fittings .

Connection options are welded and soldered seams, flanges , sleeves , pipe connecting elements , rolling , clamping rings, molded parts, screw connections and pre-bent pipe sections. Typical molded parts are T-pieces, bends 45 °, 90 ° and 180 °, as well as concentric and eccentric reductions .

It is often difficult to connect pipes made of different materials, so two metals often form a galvanic element and corrode at the connection point.


In addition to the simple cutting to length using saws or pipe cutters , pipes are increasingly being processed entirely on pipe laser machines .


AB = outside diameter
CE = inside diameter
AC = wall thickness

The dimensions of a pipe and the corresponding standard define its geometry.

  • Nominal diameter (DN = Diameter Nominal) is an integer without a unit and roughly corresponds to the inner diameter. In conjunction with a standard, it provides information about the dimensions of the pipeline. These differ depending on the standard.
  • Inside diameter (ID = Inside Diameter) in millimeters
    inside diameter = outside diameter - 2 * wall thickness
  • Outside diameter (OD) in millimeters
  • Wall thickness in millimeters

There are a variety of pipe standards for a wide variety of applications.

Plumbing pipes, heating pipes

In the past, the pipe dimensions related to the inside diameter. A 1 "pipe had a clear width of 25.4 millimeters. With the steel quality of that time, an outside diameter of about 33 millimeters resulted. The threads, fittings (angle, socket, T-piece) and tools were also manufactured to match the outside diameter. Later, when the steel quality was improved, the pipe walls could also be thinner, but since the fittings and threading tools were manufactured according to the outer diameter, the inner diameters became larger, increasing the inner volume per meter and the possible flow rate.

In heating and sanitary engineering, the customs values ​​no longer correspond to today's standards. "Inch" pipe dimensions are now defined metrically. If you find a pipe with an outside diameter of around 33 millimeters, then it is and will remain a "1-inch pipe". The standard DIN EN ISO 228-1, for example, defines the thread identification. The inside diameter of the pipe is not described in the standard, nor can it be converted from inches to millimeters.

Stainless steel pipes

The following tables provide information about the dimensions (in mm) of stainless steel pipes according to DIN , ISO and ASME :

Series A pipe dimensions according to DIN EN 10357: 2014-3 - Longitudinally welded pipes made of stainless steel for the food and chemical industry - (previous document DIN 11850) - Series 2 (expanded with DN 6 and DN 8)
Nominal size DN / DIN 6th 8th 10 15th 20th 25th 32 40 50 65 80 100 125 150 200
Outer pipe diameter [mm] 8th 10 13 19th 23 29 35 41 53 70 85 104 129 154 204
Pipe inside diameter [mm] 6.00 8.00 10.00 16.00 20.00 26.00 32.00 38.00 50.00 66.00 81.00 100.00 125.00 150.00 200.00
External dimensions (±) 0.05 0.05 0.05 0.10 0.10 0.12 0.15 0.15 0.25 0.30 0.43 0.52 0.65 0.77 1.02
Wall thickness [mm] 1.00 1.00 1.50 1.50 1.50 1.50 1.50 1.50 1.50 2.00 2.00 2.00 2.00 2.00 2.00
Wall limit dimensions (±) 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10
Weight [kg / m] 0.175 0.226 0.432 0.658 0.808 1.034 1,260 1.485 1.937 3.409 4.162 5.114 6.368 7.621 10.13
Pipe dimensions according to EN ISO 1127 - Row 1 - Stainless steel pipes -
Nominal size DN / ISO 6th 8th 10 15th 20th 25th 32 40 50 65 80 100 125 150 200
Outer pipe diameter [mm] 10.2 13.5 17.2 21.3 26.9 33.7 42.4 48.3 60.3 76.1 88.9 114.3 139.7 168.3 219.1
Pipe inside diameter [mm] 7.00 10.30 14.00 18.10 23.70 29.70 38.40 44.30 56.30 72.10 84.30 109.70 134.50 163.10 213.9
External dimensions (±) 0.05 0.05 0.10 0.10 0.12 0.15 0.15 0.20 0.25 0.30 0.44 0.57 0.70 0.84 1.10
Wall thickness [mm] 1.60 1.60 1.60 1.60 1.60 2.00 2.00 2.00 2.00 2.00 2.30 2.30 2.60 2.60 2.60
Wall limit dimensions (±) 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.12 0.12 0.13 0.13 0.15
Weight [kg / m] 0.345 0.477 0.626 0.790 1.015 1,589 2.026 2,321 2.923 3.715 4.993 6.458 8,936 10.801 14.112
Series C pipe dimensions according to ASME-BPE 1997 (stainless steel pipes according to the "Bioprocessing Equipment" standard)
Nominal size DN / OD ¼ " ⅜ " ½ " ¾ " 1" 1½ " 2 " 2½ " 3 " 4 " 6 "
Outer pipe diameter [mm] 6.35 9.53 12.70 19.05 25.40 38.10 50.80 63.50 76.20 101.6 152.4
Pipe inside diameter [mm] 4.57 7.75 9.40 15.75 22.10 34.80 47.50 60.20 72.90 97.90 146.86
External dimensions (±) 0.05 0.05 0.05 0.10 0.12 0.15 0.20 0.25 0.30 0.51 0.76
Wall thickness [mm] 0.89 0.89 1.65 1.65 1.65 1.65 1.65 1.65 1.65 2.11 2.77
Wall limit dimensions (±) 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.11 0.14
Weight [kg / m] 0.124 0.197 0.457 0.720 0.982 1.508 2.033 2.558 3.084 5.263 10,390


Web links

Commons : pipe  - collection of pictures, videos and audio files

Individual evidence

  1. a b Prof. Dr.-Ing. Roscher: Rehabilitation and renewal of supply and disposal networks. (PDF) (No longer available online.) Archived from the original on January 9, 2017 ; accessed on January 9, 2016 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.uni-weimar.de
  2. ^ Hans-Christian Sorge: Technical assessment of the condition of metallic water supply lines as a contribution to rehabilitation planning . Ed .: Dissertation at the Faculty of Civil Engineering at the Bauhaus University Weimar. Erfurt / Weimar October 30, 2006.
  3. ^ Hans-Jürgen Kocks: Operation and maintenance of steel pipelines . Ed .: GWF. 145 (2004) No. 3 , 2004.
  4. Mechanical processing ( Memento of the original from February 14, 2016 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF) service catalog of ITAG L&R GmbH, section high pressure pipes, p. 20; accessed 2016-02 @1@ 2Template: Webachiv / IABot / www.itag-celle.de
  5. Information on various plastic pipe systems at Kunststoffrohrsysteme.de
  6. Adhesive system drinking water - Friatherm Starr , Friatec AG
  7. Trevor Stafford: The European plastic pipes market: a Rapra industry analysis report . Rapra, 2001, ISBN 1-85957-237-5 .
  8. gewinde-normen.de