The gas pipeline infrastructure connects several technological levels, during which the fuel mixture is formed and delivered to the consumer. The transportation unit is based on pipes. The main supply chain of the resource, the main gas pipeline, is based on them. This is the central industrial line connecting gas production and processing stations with points of its direct distribution or consumption.
The concept of the main gas pipeline
A large-format pipeline is used to transport gas media over long distances in large volumes. The design of this structure may also include elements of control and regulatory systems and branches, but the main pipe remains the central pipe. The delivery materials can be not only gas, but also oil products, water, chemical compounds and other technological substances used in production sites or at oil and gas product processing stations.
In other words, the main gas pipeline is a universal line for transporting gas and liquid mixtures to places of consumption. What should be understood as consumers of products served by trunk pipelines? We are not talking about direct connection with end consumers, such as cottage villages or multi-storey residential buildings with production facilities. Central networks are separated from the direct sampling point by points of intermediate processing of raw materials, distribution stations, and, in extreme cases, branches that deliver gas directly to the consumer.
Gas pipeline construction
Although from the outside this structure resembles a conventional pipeline, only in a larger version, in reality the difference is significant. Even in its simplest version, the gas main pipeline contains the following structural elements:
- Directly a pipe circuit that directly interfaces with branches, transitional units, shutoff valves, etc. This is the main main part of the gas pipeline, in the body of which also connections are made to stations, control centers and treatment facilities.
- Condensate collectors and devices for introducing methanol-based technical mixtures.
- Control systems and telemechanics equipment.
- Means of providing electrochemical corrosion protection.
- Power lines and communications.
- Fire extinguishing devices.
- Tanks for gas storage and degassing.
- Service buildings for the operation of pipelines in entrusted areas.
- Pumping and intermediate pumping stations.
- Barns for gas storage.
Compressor stations as part of gas pipelines
For the comprehensive maintenance of industrial pipelines, multifunctional treatment, preparation and processing stations for serviced media are used. It is this type of technological facility that the compressor station represents. In the minimum configuration, it is based on a group of compressor shops, but in an expanded and most common form it also contains installations for filtering and air cooling of gas. The main task of such objects is to regulate the pressure of the working mixture. On medium gas pipelines, compressor stations usually maintain a design pressure level of 5-7 MPa. The principle of action usually focuses on the enhancing effect. Shut-off valves with sensitive elements automatically respond to a decrease in pressure, after which the function of the compressor shops is activated, and the standard indicator is restored.
Gas pipeline parameters
Both dimensional and technical and operational characteristics may differ depending on the functional purpose of a particular line, sampling points and delivery points, rated power, etc. Nevertheless, there are standards by which large enterprises operate. For example, Gazprom for gas pipelines establishes the following averaged characteristics:
- The diameter of the pipes is from 720 to 1420 mm.
- The working pressure on the circuit is from 5.4 to 7.5 MPa.
- Depth - 80-100 m.
- The pipe material is stainless steel.
At these operating parameters, a gas transmission network operates with a throughput of about 30-35 billion m3. Power supply capacities for service stations may vary depending on the site of operation. On average, we can talk about small indicators up to 10-15 kW.
Technological workflow
Usually a sequential transportation scheme for gas mixtures is implemented, the adjustment of which is ensured by a number of automatic units on the line. Before launching the target medium into the circuit, special preparation is performed. So that natural gas does not contain impurities, it is first cleaned. Also in the delivery process, depending on the requirements for fuel, the mixture can be filtered in separators of different systems.
Next, transportation begins along the main gas pipeline. Compressor stations, in turn, begin to monitor pressure continuously. At control centers, control is also provided by operators, which, in particular, monitor indicators of daily unevenness in gas consumption. Temperature parameters are also regulated. Already at the outlet, receiving storages or equipment of consumers may impose special requirements for gas cooling to prevent damage to small-format pipes.
Intended classification
The main task of any gas pipeline is to deliver the target mixture. But the configuration, layout, and transportation conditions may vary. This is the basis for the basic classification of gas trunk pipelines:
- Distribution systems. External lines that supply a resource from a source of production to distribution points.
- Introductory gas pipeline. This is a separate section of the transport line, which follows from the distribution node to the device at the input disconnecting the system. A kind of technological circuit, closed on a central shutoff valve.
- Initial or intermediate gas pipeline. The line connecting the disconnecting device and the internal pipeline.
- Inter-settlement gas pipeline. Such communications are laid outside settlements and can supply individual consumption objects via branches.
- Internal gas pipeline. A piece of trunk wire that originates from the lead-in line and is routed to the end gas consumer.
Pressure classification
Much depends on pressure in the operation of the gas pipeline - for example, the power of the mixture, reliability and safety. Depending on the characteristics of the medium being served, operating conditions and technical parameters, pipelines can support different pressure indicators. In particular, the following categories of lines are distinguished depending on the pressure level:
- Operating in the range of 2.5-10.0 MPa.
- Operating in the range of 1.2-2.5 MPa.
What do these indicators mean? The peak value characterizes the high productivity of the central part of the main gas pipeline - this is the segment on which the most intensive supply of the gas mixture takes place. But maximum values, however, are rare. Again, the norm is 5-7 MPa. The indicators below apply to process loops and distribution nodes. Circuits with pressure support of not more than 1 MPa are sent to residential buildings at all.
Classification by type of central part
The main body of the line is performed in different configurations. According to the requirements of the technical code of rules, gas pipelines may have the following formations of the central part:
- Straight lines. They can be simple single-strand or complex multi-strand. In the first case, the entire contour may have the same or telescopic (varying) diameter. In complex multi-strand routes, laying of parallel circuits is also provided.
- Ring lines. Usually they are built around large cities in order to increase the reliability of gas supply and maintain a uniform supply of the mixture.
Construction technology
The construction is carried out in several stages. On the basis of the project, earthwork, installation operations of laying and filling measures are carried out. First, a trench is formed with a depth of 50-150 cm. Backfill is made on its bottom with drainage layers of sand and gravel, after which support blocks based on concrete or metal are installed. On this base, in the future, direct construction of gas pipelines is carried out using welding to connect individual segments. After the installation is completed and the quality of the power fixation is checked, the line is backfilled.
Insulation for gas pipelines
A special part of the gas pipeline installation, for which a separate project can also be developed. The main requirement for the isolation of such structures is resistance to corrosion and aggressive substances in the composition of the soil. Also, the coating should be solid, waterproof, durable and heat-resistant. In the practice of building gas pipelines, the following types of insulation coatings are more often used:
- Powder-coated polyethylene factory coated sheets and dielectric properties.
- Polyethylene based coatings for route laying. This is a wide group of insulators that can be performed in tape form or as part of a bitumen mixture. The second option is resistant to high temperatures.
In some cases, the functions of insulators for main gas pipelines can also be performed by paints and varnishes like epoxy paint. But such solutions are only valid for ground loops, since this type of protective coating will require regular updates.
Operation of gas mains
The gas pipeline work process is supported by appropriately qualified management organizations. In particular, gas transmission companies may conclude an agreement with the owner of the facility, in accordance with which they undertake to ensure safe and reliable gas supply to consumers. During operation, the linear production management of gas pipelines will provide for the regulation of valves on the control nodes, the implementation of reconstruction measures, the examination of functional parts, etc.
Gas line maintenance
Gas pipelines are regularly patrolled to detect problems or malfunctions in certain areas. After analysis of possible accidents or breakdowns, a plan of repair procedures is drawn up. Next, preparations are made for work with cleaning the work area. The nature of the repair of the main gas pipeline depends on the location of the breakdown and its severity. The technical control service, in particular, can correct the position of valves, control and measuring devices and eliminate the leakage of fasteners. As preventive repair and restoration procedures, replacement of fences, painting of structures, strengthening of support blocks and restoration of insulation contacts with dielectrics are carried out.
Conclusion
The specifics of the construction and operation of gas pipelines are, in principle, determined by increased requirements for the service environment. Security issues from this point of view play a special role, which is reflected in the linear management of gas pipelines, which involves ensuring integrated and constant monitoring of the operating parameters of the system. Along with pressure, indicators of flow, temperature, humidity and the state of electromechanical circuits are recorded. These and other network parameters allow you to control the performance indicators of gas supply to target objects. Technically, such tasks are realized with the help of automatic equipment, which are equipped with the same control centers and compressor stations.