Pipes connect various apparatuses of chemical plants. They are used to transfer substances between different communications. The design includes several separate pipes, which, with the help of connections, form a single pipeline system.
Piping system
Pipeline - a system of cylindrical components connected by connecting elements and used to transport chemicals and other materials. As a rule, underground pipelines are used in chemical plants to transport substances. As for the autonomous and isolated parts of the installation, they also apply to the piping system or network.
Autonomous piping system configuration may include:
- Pipes.
- Connecting fittings.
- Seal connecting two removable sections.
All of these elements are produced individually, after which they are connected as a single pipeline system. In addition, pipelines can beequipped with heating and the necessary insulation in different materials.
The size of pipes and materials for their manufacture is selected based on the requirements of the process and the discharge set in each individual case. But in order to standardize the dimensions of pipelines, they were classified and unified. The key criterion is the allowable pressure at which the operation of the pipeline is possible and safe.
Nominal diameter
Nominal diameter is a parameter used in piping systems as a performance factor that aligns parts such as pipes, valves, fittings in hydraulic piping calculations.
Nominal diameter - volumetric value, numerically equal to the internal diameter of the structure. Example of nominal inside diameter: DN 125.
Nominal inside diameter is not indicated on the drawings and does not replace actual pipe diameters. It approximately corresponds to a clear diameter for certain sections of the pipeline in the hydraulic calculation. If numeric nominal diameters are implied, they are chosen to increase the capacity of the pipeline by up to 40% from one nominal diameter to the next.
Nominal diameters are set to avoid problems with mutual alignment of parts when calculating the hydraulic losses in the pipeline. When determining the nominaldiameter, based on this value, an indicator is selected that is as close as possible to the diameter of the pipe.
Nominal pressure
Nominal pressure is the value corresponding to the maximum pressure of the pumped medium at 20 °C, which ensures long-term operation of the pipeline with the specified dimensions. The nominal pressure - a dimensionless value - has been calibrated based on accumulated operating experience.
The nominal pressure for the pipeline when calculating hydraulic losses is selected based on the pressure created in it during operation by choosing the largest value. In addition, fittings and valves must also correspond to the same level of pressure in the system. The pipe wall thickness is calculated based on the nominal pressure and ensures that the pipe can operate at a pressure equal to the nominal pressure.
Permissible operating overpressure
Nominal pressure applies only at 20°C operating temperature. As the temperature rises, the load on the pipe decreases. At the same time, the allowable overpressure is correspondingly reduced. This value indicates the maximum overpressure that can be in the pipeline system when the operating temperature value increases when calculating the hydraulic resistance of the pipeline.
What are pipelines made of?
When choosing materials for the manufacture of piping systems, characteristics are taken into account, such as the parameters of the medium to be transportedthrough the pipeline, and the preliminary working pressure in this system. The possibility of a corrosive effect of the internal environment on the wall material should also be taken into account in the hydraulic calculation of heating pipelines.
Most piping systems are made from steel. Gray cast iron or unalloyed constructions are used for piping where there are no high mechanical loads or corrosive effects.
In the hydraulic calculation of heating pipelines at high operating pressure and the absence of loads with an active effect of corrosion, a pipeline made of improved steel castings is used.
When the average corrosion resistance is high or the purity of the product is strict, the piping is made of stainless steel.
If the pipeline system must withstand the influence of sea water, copper-nickel alloys are used for its production. Aluminum alloys and metals such as tantalum or zirconium are also used.
Various types of plastics are often used as tubing materials in hydraulic design of pressure pipelines due to its high corrosion resistance, low weight and ease of processing. This material is suitable for sewage pipelines.
Piping elements
Plastic pipes are suitable for welding and are designed on site. Such materials include steel, aluminium, thermoplastic, copper. To connect directsections of pipes, specially made shaped elements are used, for example, splitters and diameter reducers. Such fittings are included in any pipeline system.
Special connections are used for mounting individual parts and fittings. They are also used to connect the necessary valves and apparatus to the pipeline.
Connecting elements are selected depending on the following parameters:
- Materials used for the production of pipes and fittings. The main selection criterion is the ability to weld.
- Working conditions: low or high pressure and low or high temperature.
- Manufacturing requirement for piping system: fixed or removable connections in piping system.
Linear expansion of pipes and its compensation
The geometric shape of objects can be changed both by force action and by changing their temperature. These physical phenomena cause the pipeline to undergo some linear expansion or contraction during the installation phase under shock-free conditions and without thermal influence, negatively affecting its functional characteristics, when serviced due to pressure and temperature.
When expansion is not required to compensate, deformation of the piping system occurs. Doing so may damage flange seals and pipe connections.
Thermal linear expansion
When calculating the hydraulicThe resistance of the pipeline and installation must take into account the potential change in length due to temperature rise or the so-called thermal linear expansion. This value is equal to the value of the linear expansion of pipes 1 m long with a temperature increase of 1 °C.
Example of hydraulic calculation of pipelines: Q=(Πd²/4) w
Pipe insulation
When a high-temperature medium is transported through a pipeline, it should be insulated to avoid heat loss. If a low temperature medium is transported through a pipeline, insulation is used to prevent it from heating up. In such cases, the insulation is made using special insulation materials wrapped around the pipes.
Typically, the following materials are used:
- At low temperatures up to 100 °C - rigid foam (polystyrene or polyurethane).
- At average temperatures around 600°C - in the form of sheaths or mineral fibers such as stone wool or glass felt.
- At high temperatures around 1200 °C - ceramic fiber (aluminum silicate).
Pipes with a nominal inside diameter below DN 80 and an insulation layer thickness of less than 50 mm are usually insulated with insulating molded elements. To this end, two shells are wrapped around the pipe and secured with metal tape, and then closed with a tin plate case.
Nomogram for hydraulic calculation of pipelines
Pipelines with nominalinternal diameters over DN 80 must be equipped with thermal insulation having a bottom shell. Such a sheath contains clamping rings, staples and a metal lining made of galvanized mild steel or stainless steel sheet. The space between the pipeline and the metal case is filled with insulating material.
The thickness of the insulation is calculated as a determination of production costs and losses that occur due to loss of heat, and ranges from 50 to 250 mm.
Table for hydraulic calculation of pipelines
Proper selection of piping system insulation solves numerous problems such as:
- Avoid sudden drop in ambient temperature and save energy as a result.
- Preventing temperatures in gas transmission systems from falling below the dew point, which prevents condensation from forming and can cause serious damage.
- Avoiding condensate emissions in steam lines.
Example:
| Material | Movement speed, m/s | ||
|---|---|---|---|
| Liquid | Spontaneity: | ||
| Viscous substance | 0, 1 – 0, 5 | ||
| Low viscosity components | 0, 5 – 1 | ||
| Pump: | |||
| Suction | 0, 8 – 2 | ||
| Injection | 1, 5 – 3 | ||
Thermalinsulation must be applied along the entire length of the piping system. Flanged connections and valves must be provided with molded insulating elements. They provide unobstructed access to connection points without the need to remove the insulation material from the entire piping system in case an air seal breaks.
