Piping

Pipelines used to transport fluids (gases, liquids or pourable or pumpable solids). Constituents are in particular pipes, pipe fittings, expansion joints, fittings, gaskets, fasteners such as flanges, fittings, couplings, sleeves and fasteners (pipe support). In a broader sense, also the pump, any heat or cold insulation as well as monitoring systems to this compilation. These items are often subject to standardization. Thus, it is possible to create a pipeline from a modular system. Individual pipes can be joined to all networks, the individual power supplies are protected against each other by Erstabsperrungen.

Pipelines are executed in the nominal diameter of a few millimeters to several meters and, in the case of a pipeline to reach the length of thousands of kilometers. The pressure rating can range from bar vacuum to a few hundred. Hydraulic pipes have outer diameter 4-80 mm and are designed for calculating pressures 120-750 bar ( according to EN 13480 for material P235TR2 ). The selection of materials of a pipeline depends on static and dynamic loads (eg nominal pressure, traffic loads, earth pressures, pressures from inside or outside, pressure surge ), mechanical stress ( for example, flow rates, bed materials), corrosive conditions and the nature and temperature of the to transporting material.

Certain design requirements for piping as nominal pressure rating, materials, flange, seals, etc. are defined in the so-called pipe classes.

Depending on the temperature of the transporting material or the ambient temperature may require insulation, pipe heating or cooling, but also, for example, a leakage monitoring of the pipeline.

Piping with an allowable internal working pressure of about 0.5 bar are in accordance with the Pressure Equipment Directive 97/23/EC a " pressure equipment" and may only be brought in accordance with this Directive in traffic.

Historical pipelines

Even in ancient pipes were used for water supply ( eg in Pergamon or in Cologne). They were usually part of aqueducts to overcome as pressure lines in height. An example of a pressure pipe (siphon) from the Middle Ages is the Tiergarten tunnel in Blankenheim. The tubes designated as Deichel or Teuchel were made ​​of wood.

Planning documents

In the design, planning and construction of pressure piping systems in large facilities such as power plants, refineries and manufacturing plants in the chemical industry, the individual planning steps occur with the creation of the following planning funds from:

• The basic flowsheet
• The process flow diagram
• The piping and instrumentation diagram
• The installation and the piping diagram
• The pipeline isometry with the associated BOMs
• The pipeline design list
• Further inspection plans and quality assurance plans

With the help of these planning documents it is possible to plan a specific piping structure such as a large power plant and build.

Pipes of plastics

In recent years, pipelines have gained increasing importance of plastics. You are now at 54% market share and a volume of 2.5 million tons / year, the most important materials for pipe systems in Europe. The most commonly used systems of polyethylene ( PE), cross-linked polyethylene (PE -X ), polypropylene (PP ) and polyvinyl chloride (PVC -U) for water supply, sewerage, gas supply, heat supply (only PE -X and PP), and industrial piping employed.

A continuous growth for the coming years is expected for plastic piping systems, based mainly for PE on the rehabilitation of existing water supply lines and for PVC -U and PP on the wastewater sector.

See, for example, polyethylene pipe

Interpretation of a pipeline

The aim of the pipeline design is the determination of

• Nominal width
• Flow rate (high speed means more flow noise and higher pressure losses due to pipe friction losses )
• Nominal pressure (indirect determination of a sufficient wall thickness)
• Holder concept
• Material
• Routing
• Gradient ( for example, waste water)

Pipe class

To start planning is a specification that is called in this case, pipe class, created. Here, everything is described, which is crucial for the selection of piping components. In essence:

• Operating conditions

• Medium
• Temperature
• Pressure
• Mass flow rate
• Economic backgrounds
• Costs
• Availability of spare parts

Nominal width

Depending on the desired mass flow and the maximum accepted pressure drop ( at the maximum planned flow rate ) a certain tube cross section is calculated. In the selection of the pipe is calculated and - if not present by default - select the next higher nominal inside diameter. Nominal diameter are a normalized - and optimized - Increments of pipe inside diameters to minimize the number of variants of the tubes used.

The pressure drop is an important criterion for the design of a pipeline. The pressure drop value is very sensitive to changes in the pipeline sense diameter. The flow pressure loss of a conduit is changed at a given flow rate with the fourth power of the diameter.

Benefits of greater dimensions:

• Lower pressure loss
• Lower flow noise
• Larger span of the pipe mounting (less mounting holes)
• Less energy expenditure Pipeline transportation

Disadvantages of a larger dimension

• If necessary. greater heat loss
• Higher investment costs
• Larger footprint
• Larger mass (weight)
• Less flexibility (eg elastic modulus and strength for plastic pipes )
• Higher forces from strain due to temperature

There is talk of an economic dimension when offset the costs of the aforementioned properties.

Flow rate

To avoid collisions by acceleration or deceleration, the flow rate should be kept the same in pipes. In the literature, the following guidelines are:

Sources:

• Dubbel = dubbels Paperback for mechanical engineering; Vol 1; 1956
• Steinmueller = STEINMÜLLER Paperback pipeline engineering; 1988

The decisive factor for the dimensioning is the economic speed. It results from the optimum of the sum of the capital cost of the pipeline, the investment costs of the machinery (pumps, compressors) and the energy and maintenance costs over the entire period of operation.

Nominal pressure

For the pipe components, there are many binding to manufacturers standards. The determination of the required wall thickness ( after the boiler formula ) is included in these standards.

For those planning a nominal pressure must be chosen, which must always be above the operating pressure maximum occurring naturally. High operating temperatures must be taken into account, because this is the material strength decreases. Thus, the increase in the nominal pressure by one or several steps may be necessary.

Solids

Pipes for solids (eg, granules, flour, dust) are often referred to as a chute. They can be found for example in the cement industry or in mills for grain. They are characterized by large radii at changes in direction, the associated pipe bends are often made ​​of a highly wear-resistant material to artificial basalt.

Furthermore, solids can settle inside of pipes during normal operation. These deposits can lead to blockage of the flow to a blockage of the line and must be periodically removed by a pipe cleaning.

Operational safety

As an important component of technical systems piping shall ( reliability ) are maintained in the course of plant safety. This is particularly true for pipelines that need to comply with other physical properties such as a certain coefficient of friction or heat transfer coefficients in addition to the tightness. Special rules apply to compression-loaded pipes and the corresponding flow media, such as pipelines for water vapor in steam power plants. Pipes with an internal gauge pressure greater than 0,5 bar for flammable, highly flammable, extremely flammable, corrosive, toxic or very toxic gases or liquids are classified installations for the purposes of industrial safety regulations and must, depending on the hazard potential by approved inspection bodies or competent persons before starting up and within certain time limits are checked. Maintenance includes:

• Inspection measures at regular intervals (eg visual inspection, non-destructive testing ( ultrasound, x ), pressure test, tests of the bearings and suspension)
• Corrosion protection measures
• Pipe cleaning