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Pipelines in an industrial plant
Mostly thermally insulated pipes in a boiler room

Pipelines are used to transport of fluids ( gases and liquids ) and free-flowing or pumpable solids as well as the transmission of mechanical and thermal energy.


Pipeline parts and fittings made of stainless steel
Device for cleaning pipes

Components are in particular pipes , pipe fittings, expansion pieces, fittings , seals , connecting elements such as flanges , fittings , screw connections , sleeves and the fastening elements ( pipe supports ).

In a broader sense, the pumps , any heat or cold insulation and monitoring systems also belong to this compilation. These individual parts are often subject to standardization . It is thus possible to assemble a pipeline as if from a construction kit . Individual pipelines can be joined together to form entire networks; the individual network parts are secured against each other by initial barriers.

Pipelines are designed with a nominal width ( diameter ) of a few millimeters to a few meters and, in the case of a pipeline, can be thousands of kilometers in length. The nominal pressure levels can range from a vacuum to a few hundred bar . Hydraulic pipes have an outside diameter of 4–80 mm and are designed for calculation pressures between 120 and 750 bar (according to EN 13480 for material P235TR2).

The choice of materials for a pipeline depends on static and dynamic loads (nominal pressure level, traffic loads, earth pressures, pressures from inside or outside, pressure surge ), mechanical stresses (e.g. flow speeds, debris), corrosive stress and the type and temperature of the material to be transported.

Certain constructive specifications for pipelines such as nominal pressure level, materials, flange designs, seals, etc. are defined in so-called pipe classes . Depending on the temperature of the material to be transported or the ambient temperature, thermal insulation , pipe heating or cooling , but also leak monitoring of the pipe may be necessary. Pipes with a permissible internal operating pressure of over 0.5 bar are " pressure equipment " according to the Pressure Equipment Directive 97/23 / EC and may only be brought into circulation in accordance with this directive.

Historic pipelines

Historic water pipeline

Pipelines were already used for water supply in ancient times, for example at Pergamon or in Cologne (see Eifel aqueduct ). They were mostly part of aqueducts in order to be used as pressure pipes to overcome height differences. An example of a pressure pipe (siphon) from the Middle Ages is the zoo in Blankenheim .

Historic wooden water pipes are called Deichel or Teuchel. Drilled tree trunks were joined together to create water pipes. Dyke water pipes were still in use in many places in the 20th century.

Planning documents

When designing , planning and building pressure pipelines in large-scale plants such as power plants , refineries and production facilities in the chemical industry , the individual planning steps include the creation of the following planning tools:

With the help of these planning documents it is possible to plan and build a structure determined by pipelines, such as a large power plant.


Various specifications are made when laying out pipelines:

  • Selection of the material depending on the expected mechanical and corrosive stress
  • Dimensioning
    • the nominal size according to the desired flow velocity ( pipe size determination )
    • the wall thickness according to the expected nominal pressure
  • Laying and course (alignment), taking into account
    • the fastening (fixed and loose bearings), and if necessary
    • the expansion compensation for temperature fluctuations and des
    • Slope (e.g. in sewer pipes )

Pipe spec

At the beginning of the planning, a specification is created, which in this case is called a pipe spec . It is decisive for the selection of the pipeline components and is usually determined according to the following operating conditions:

  • medium
  • temperature
  • pressure
  • Mass throughput
  • economics
  • Spare parts availability

Nominal size

A certain pipe cross-section is calculated depending on the desired mass flow and the maximum accepted pressure loss (at the maximum intended flow velocity ) . When selecting the pipe, the calculated or - if not available as standard - the next higher nominal inside diameter is selected. Nominal diameters are a standardized - and optimized - gradation of internal pipe diameters in order to minimize the number of variants of the pipes used.

The pressure loss is an essential criterion for the design of a pipeline. The pressure drop value reacts very sensitively to changes in the internal pipe diameter . The flow pressure loss in a pipeline changes with the fourth power of the diameter for a given throughput .

The economic dimension with minimal costs is achieved when the following properties are optimally balanced. So result from a larger dimension both

Flow velocity

In order to limit the pressure loss due to pipe friction, local pressure surges and flow noises and to avoid cavitation in liquids, certain flow velocities in pipes should not be exceeded.

Guide values ​​flow velocities for oil, water, steam and gas pipes  
oil source
Heavy oil, heated, pressure lines 1 - 2 m / s Steinmüller
Heavy oil, heated, suction lines 0.5 - 1 m / s Steinmüller
Lubricating oil 0.5 - 1 m / s Dubbel
Petrol, kerosene: DN 25 5 m / s * Steinmüller
Petrol, kerosene: DN 100 2.5 m / s * Steinmüller
Petrol, kerosene: DN 200 1.8 m / s * Steinmüller
water source
Suction lines, depending on length and temperature 0.5 - 2.0 m / s Steinmüller
Centrifugal pump suction lines 1.0 - 1.5 m / s Dubbel
Piston pump suction lines 0.8 - 1.0 m / s Dubbel
Pressure lines, with constant operation 1.5 - 5.0 m / s Steinmüller
Pressure lines, in case of emergency or bypass operation 4.0 m / s Steinmüller
Pressure lines if there is a risk of corrosion from O 2 5.0 m / s Steinmüller
Pressure lines from centrifugal pumps 2.5 - 3.0 m / s Dubbel
Pressure lines of piston pumps 1.0 - 2.0 m / s Dubbel
Utility water pipes 4.0 - 6.0 m / s Steinmüller
Cooling water pipes 1.5 - 2.5 m / s Steinmüller
Condensate lines 1.0 - 2.0 m / s Steinmüller
steam source
Saturated steam for production lines 25 - 30 m / s Steinmüller
Superheated steam, 40 bar in the power plant 30 - 40 m / s Steinmüller
Superheated steam, 80 bar in the power plant 16-22 m / s Steinmüller
Superheated steam, 120 bar in the power plant 15-20 m / s Steinmüller
(for short lines up to 50% higher values) Steinmüller
Main steam lines of large boiler units 40 - 60 m / s Steinmüller
Turbines, superheated steam, small power 35 m / s Dubbel
Turbines, superheated steam, medium power 40 - 50 m / s Dubbel
Turbines, superheated steam, great performance 50 - 70 m / s Dubbel
Turbines, saturated steam 25 m / s Dubbel
Turbines, exhaust steam 15 - 25 m / s Dubbel
Piston steam engines, superheated steam 40 - 50 m / s Dubbel
Piston steam engines, saturated steam 25 - 30 m / s Dubbel
gas source
Low pressure, long lines 5 - 10 m / s Steinmüller
High pressure, short lines 20 - 30 m / s Steinmüller
* Guide value for avoiding electrostatic charging with highly flammable mineral oil products


  • Dubbel = DUBBEL's pocket book for mechanical engineering; Part 1; 1956
  • Steinmüller = STEINMÜLLER Pocket Book Pipeline Technology; 1988
Guide values ​​flow velocities in air lines and ducts  
air Lounges Industry source
Compressed air in company networks 2 - 10 m / s Steinmüller
Warm air for heating purposes 0.8 - 1.0 m / s Steinmüller
Piston compressor, suction line 16-20 m / s Dubbel
Reciprocating compressor, pressure line 25 - 30 m / s Dubbel
Turbo compressor, suction and pressure line 20-25 m / s Dubbel
Outside air grille 2 - 3 m / s 4 - 6 m / s Bosy
Main channels 4 - 8 m / s 8 - 12 m / s Bosy
Branch ducts 3 - 5 m / s 5 - 8 m / s Bosy
Exhaust grille 1.5 - 2.5 m / s 3 - 4 m / s Bosy
  • Dubbel = DUBBEL's pocket book for mechanical engineering; Part 1; 1956
  • Steinmüller = STEINMÜLLER Pocket Book Pipeline Technology; 1988
  • Bosy = guideline values ​​for the choice of speeds, according to the permissible noise level and pressure loss

The decisive factor for the dimensioning is the economic speed . It results from the optimum of the sum of the investment costs for the pipeline, the investment costs for the machine system (pumps, compressors) and the energy and maintenance costs over the entire operating time.

In addition to the properties of the medium, the pipe profile and course and the surface of the pipe wall, the flow velocity is decisive for the formation of a laminar or turbulent flow .

Nominal pressure

There are many standards that are mandatory for manufacturers for pipeline components. The determination of the necessary wall thickness (according to the boiler formula ) is taken into account in these standards.

A nominal pressure must be selected for planning, which of course must always be above the maximum operating pressure that occurs. High operating temperatures must be taken into account because this reduces the material strength. It may be necessary to increase the nominal pressure by one or more levels.

Pipelines for solids

Tube sheet in a modern flour mill

Pipelines for solids (e.g. granules , flour , dust ) are often referred to as chutes . They can be found, for example, in the cement industry or in mills for grain . They are characterized by large radii when changing direction, the associated pipe bends are often made of a particularly wear-resistant material or even artificial basalt .

Furthermore, solids can accumulate inside pipelines during normal operation. These deposits can block the flow or even block the line and must therefore be removed regularly by cleaning the pipe .

Operational safety

Pipelines in a chemical factory

The standard pipeline identification provided makes maintenance and repair work easier in the event of a fault.

As an important component of technical systems, pipelines must be maintained in the course of system safety (operational safety). This applies in particular to pipelines, which, in addition to tightness, have to meet other physical properties such as a specific coefficient of friction or heat transfer coefficient. Special regulations apply to pressure-loaded pipelines and the corresponding flow media, for example pipelines for water vapor in steam power plants .

Pipelines with an internal overpressure of more than 0.5 bar for flammable, highly flammable, extremely flammable, caustic, poisonous gases or liquids are systems that require monitoring within the meaning of the Industrial Safety Ordinance and, depending on the risk potential, must be carried out by approved monitoring bodies or qualified persons before commissioning and regularly within certain deadlines being checked.

Maintenance includes:

Classification according to materials


In recent years, plastic pipelines have become increasingly important. With a 54% market share and a volume of 2,500,000 tons / year they are now the most important materials for pipe systems in Europe. Systems made of polyethylene  (PE), cross-linked polyethylene (PE-X), polypropylene  (PP) and polyvinyl chloride  (PVC-U) are used most frequently in the areas of water supply, sewage disposal, gas supply, heat supply (only PE-X and PP) and industrial pipelines .

Continuous growth is also expected for pipe systems made of plastic in the coming years, based above all on the renovation of existing water supply lines for  PE and on the sewage sector for PVC-U and  PP .


In building technology , pipes made of copper in the degrees of hardness soft ( R220 ), semi-hard ( R250 ) and hard ( R290 ) are mainly used.

Soft pipes must not be used for gas and solar installations. Copper press fittings are made from copper Cu-DHP material CW024A, for example.

Copper corrodes through contact with ammonia and nitrate in a moist environment. Thermal insulation of the pipes should therefore be free of these substances. Cold water pipes in particular should be protected from condensation. Traditionally, the pipe was coated with vaseline (petrolatum) or wrapped with bandages that were soaked with vaseline for protection against corrosion . Today, copper pipes are often used, which are provided with a plastic coating at the factory.

Copper pipe that comes into contact with plaster containing gypsum should be provided with a plastic bandage made of adhesive tape or a plastic cover ex works. This is especially true in humid environments and with gas installations.

stainless steel

In building technology , pipelines made of stainless steel of the qualities 1.4520 , 1.4521 , 1.4571 , 1.4401 , 1.4404 and Cr-Ni steel 1.4301 are mainly used.

In contrast to " austenitic steels ", Cr-Mo-Ti steels without nickel are also referred to as "ferritic steels".

Just like non-galvanized, so-called carbon steel pipes and galvanized steel pipes, 18/10 Cr-Ni steel 1.4301 should not be used for drinking water due to its sensitivity to corrosion . While ordinary steel always corrodes, it depends on the composition of the water whether galvanized steel and certain stainless steel alloys are also attacked. Steel grade 1.4301 in particular is sensitive to chloride ions . But also with other stainless steel pipes in cooling and drinking water installations the content of water-soluble chloride ions should not exceed a value of 250 mg / l. According to DIN 1988 Part 7, the material for the thermal insulation of stainless steel pipes must not contain a mass fraction of water-soluble chloride greater than 0.05%. (AS-quality insulation material (see also AGI Q135) contains significantly less chloride.)

Stainless steel pipe that comes into contact with plaster containing gypsum should be provided with a plastic coating for gas installations.

The expansion coefficient of grade 1.4401 is 0.0165 mm / (m · K) significantly higher than that of grade 1.4521 with 0.0104 mm / (m · K), while the thermal conductivity is about a third lower.

Today, stainless steel pipes are predominantly connected with press fittings . The fittings are often made of 1.4401 steel or gunmetal . Gunmetal fittings should not be used with district heating water above 120 ° C, saturated steam, treated water, gray and black water with a pH value above 6, sprinkler pipes and dry fire-fighting water pipes . In sanitary and heating installations, pipes and fittings made of stainless steel should not have any direct contact with pipes and fittings made of unalloyed steel ( carbon steel or black steel ). The smallest possible bending radius of pipes up to 28 mm outside diameter is given as three and a half times the outside diameter of the pipe. Special methods are required to bend thicker pipe.

Stainless steel pipe materials in plumbing and heating installations  
Material number alloy description Properties and areas of application Manufacturer identification Approvals
1.4401 (AISI 316) X 5 CrNiMo17-12-2 high-alloy, stainless, austenitic Cr-Ni-Mo steel universal pipe and fitting material for drinking water, gas, etc. as tube blue (VSH) or yellow (walnut)
1.4404 X 2 CrNiMo17-12-2) like 1.4401 with a lower carbon content similar to 1.4401
1.4520 (AISI 439) X 2 CrTi17 stainless ferritic Cr steel titanium stabilized not suitable for drinking water; z. B. for closed circuits (heating, solar, cooling systems), compressed air, stationary sprinkler systems according to FM or LPCB, shipbuilding; Alternative to AISI 304, but without nickel z. B. black (walnut) DVGW GW 541
1.4521 (AISI 444) X 2 CrMoTi18-2 Especially for drinking water, not approved for gas, only to a limited extent for oils and industrial applications, not recommended for sprinkler, extinguishing water pipes or saturated steam> 120 ° C often green (walnut)

For rainwater, post-treated water (partially and fully demineralized water, demineralized, deionized, osmosis and distilled water), solar and cooling systems, water vapor, sprinkler systems, compressed air, vacuum, oil, carbon dioxide, helium, ethanol, acetone, nitrogen, forming gas , Noble gas and air containing ammonia are suitable for all four materials.

Carbon steel

Threaded pipes

In addition to lead and later copper pipes, so-called black pipes were predominantly used in building technology for heating installations and galvanized steel pipes for drinking water installations. These are standardized as heavy or medium-weight , so-called boiling tubes . The steel pipes were provided with pipe threads for connection . Un-galvanized pipes were also welded.

Carbon steel pipes or precision steel pipes

In building technology , sendzimir galvanized pipes are predominantly used, which may also be given a passivating chrome coating. The connection is usually made using clamp and press fittings. Press fittings are made from steel grade RSt 34-2, for example.

To ensure dimensional accuracy, only a thin layer of zinc is applied, which is not very durable when exposed to moisture. For use in permanently moist or corrosive environments, pipes with a protective layer made of plastic are offered (e.g. polypropylene coating at VSH / Seppelfricke ). Cold water pipes are protected against condensation (and heating) in accordance with DIN 1988 Part 200.

Pipes for closed circuits in heating, cooling and solar systems as well as for compressed air are only galvanized on the outside. To distinguish them from stainless steel pipes, carbon steel pipes are often given a red label by the manufacturers.

Pipes for sprinkler systems are galvanized inside and out and made, for example, from material 1.0031 ( VSH / Seppelfricke ).

See also


  • Hans Burkhard Horlacher, Ulf Helbig (Ed.): Pipelines. 2nd Edition. Springer Verlag, Berlin / Heidelberg 2016, ISBN 978-3-642-39781-3 .
  • Heinz W. Richter (Ed.): Repair of pipelines. Volume 1, Vulkan Verlag, Essen 2004, ISBN 3-8027-2730-4 .
  • Günter Wossog (Ed.): Handbook of pipeline construction. 2nd Edition. Vulkan Verlag, Essen 2003, ISBN 3-8027-2723-1 .

Web links

Wiktionary: Pipeline  - explanations of meanings, word origins, synonyms, translations
Commons : Pipelines  - collection of images, videos and audio files

Individual evidence

  1. Bruno Bosy: Pneumatic adjustment In: Bosy-Online.de, accessed in May 2018.
  2. a b c d e f g h i VSH Technical Manual XPress
  3. a b Terms, data, technical rules for gas installation: Tips for practice , page 24, updated 2010 edition. Publisher: ASUE Working Group for Economical and Environmentally Friendly Energy Consumption eV, www.asue.de and DVGW German Association of Gas and Water Industry eV - Technical-scientific association
  4. Technical instructions for V-profile fittings , In: www.eurotubieuropa.it
  5. a b c "The Geberit" planning manual - Planning with Geberit products (PDF).
  6. according to TI "Treated Waters"
  7. a b c d e f g Product manuals Optipress-Aquaplus , press system with stainless steel and gunmetal fittings for stainless steel pipe; Optipress-Therm , press system with zinc-nickel-coated fittings for carbon steel or precision steel pipe and Optifit-Press , press system with zinc-nickel-coated fittings for threaded pipe and boiler pipe , R. Nussbaum AG, Olten, Switzerland
  8. Geberit plumbing planning manual (PDF), valid from January 1, 2016.