The gas distribution system is a complex of interconnected facilities, the main purpose of which is to supply “blue fuel” to the consumer. When assembling such networks, of course, all the required technologies must be followed. Laying a gas pipeline is a responsible matter, and safety should not be neglected when performing such work in any case.
The main components of the gas pipeline
Networks designed to transport “blue fuel” include:
- external highways of settlements;
- means of electrochemical protection;
- regulatory points;
- automated control systems;
- internal highways.
External gas pipelines are pipes stretched outside buildings to the case or disconnecting device when entering the premises. An internal system is pipes laid from an external structure to consumers (stove, boiler). Methods for laying a gas pipeline can be different.
Types of systems
There are classified the lines designed for the supply of "blue fuel", according to several criteria:
- type of gas (LPG, natural);
- the number of pressure control stages (single or multi-stage);
- designs (deadlock, ring, mixed).
In settlements for use by owners of houses and apartments, mainly natural gas is supplied. LPG (liquefied) on highways is rarely transported. In most cases, it is pumped into cylinders. LPG is supplied through pipes only if there is a tank unit or regasification station in the village.
In cities and large towns, a multi-stage distribution gas pipeline is usually laid. Assembling a single-stage low pressure is very expensive. Therefore, it is advisable to install such systems only in small villages. When assembling multi-stage gas pipelines, regulatory points are established between branches of different pressures.
Actions before laying
Before proceeding with the assembly of the gas pipeline:
- calculate the required amount in a particular locality of gas;
- determined with the diameter of the pipes;
- Determined with the need to install automated control systems;
- make up the project of an external gas pipeline.
Consumers are usually responsible for assembling the internal gas supply systems. The boilers and stoves are connected by agreement with the owner of the house, licensed companies of the corresponding specialization.
Calculation of the required gas
Such planning takes into account:
- population and building density;
- lack or availability of hot water.
Calculate the estimated maximum gas flow rates. For example, for settlements with the number of people living from 700 to 2000 and a building density of 150-960 m 2 / ha, this figure will be 0.7-1.6 m 3 (h · people). In the absence of hot water, the estimated maximum flow rate is reduced by 25%. They carry out the calculation taking into account the development prospects of a village or city for 10 years in advance.
Pipe calculation
The required diameter of the external gas pipelines is selected based on:
- estimated consumption of "blue fuel" during hours of maximum consumption;
- pressure loss in the line.
Preliminary diameter calculations are performed according to the formula
d = 3.62 * 10 -2 √ Q h (273 + t) / P m v,
where Q h is the hourly flow rate at normal pressure, P m is the absolute pressure in the section, and v is the gas velocity.
Subsequently, adjustments are made to the results obtained depending on the resistance in the line (fittings, connections, turns). To determine the pressure drop, special formulas are used (for each gas supply mode - its own).
Installation of external gas pipelines: automated control systems
Such equipment is designed to provide the highest performance lines. Automated control systems (ACS TP RG) have a centralized structure. Their main elements are:
- controlled points (KP) installed on external highways;
- central control room (upper level).
- gas distribution systems (lower level).
The central control center includes several workplaces united by means of computer networks. The automated control system for gas pipelines
- for the purpose of operational control of distribution;
- equipment condition monitoring;
- accounting for gas intake and consumption.
How can highways be laid?
It is allowed to pull the gas pipeline underground or above ground. The latest technology is the most economical. The method of laying underground is considered safer. This is how gas pipelines are usually pulled along populated areas . However, the implementation of such a technique is more expensive. In maintenance, such a highway is also more costly.
Some sections of the network in large settlements can also be laid above the ground. But they are almost never too long. An overhead gas pipeline is also provided on the territory of industrial enterprises.
Before starting the installation of the network, its scheme is compiled without fail. The highway project, according to the standards, must be implemented in a topographic plan.
Underground gas pipeline construction: rules
On-site assembly of the gas pipeline is carried out in compliance with the following standards :
- the distance between the gas pipeline and other ground communications should not be less than 0.2 m;
- at the intersection with the communication manifolds, the pipes extend in a case;
- gas pipelines are laid above other engineering systems;
- cases beyond the intersection are displayed at a distance of at least 2 m;
- the ends of the cases are sealed with waterproofing materials.
The gas pipeline laying depth should be at least 0.8 m according to the standards. But as a rule, trenches for such systems are dug out by one or more meters. In any case, the laying depth should be such that the temperature of the pipe wall does not fall below 15 degrees.
Pipe requirements
Blue fuel can be supplied in underground systems via steel or polyethylene highways. Corrosion resistance and relatively low cost are considered an advantage of the latter . However, the use of polyethylene pipes for transportation of “ blue fuel” is far from always permissible. For example, laying underground pipelines using such material is impossible :
- on the territory of settlements with a gas pressure of more than 0.3 MPa;
- beyond the territory of settlements at a pressure of more than 0.6 MPa;
- for the liquid phase of SSU;
- when the wall temperature of the pipeline is below 15 degrees.
The strength factor of pipes used for laying gas outdoor networks should be at least 2.
Steel gas pipes can be both seamless and welded. For the underground system, similar highways with a wall thickness of at least 3 mm can be used. It is allowed to use both straight-line pipes and with a spiral seam for gas transportation.
Underground trunking technology
Such systems are assembled as follows:
- marking of the construction strip and geodetic breakdown of horizontal and vertical corners of turns;
- earthworks are carried out with a single-bucket excavator with a backhoe;
- manual completion of the trench;
- the bottom of the trench is leveled;
- just before laying, pipes are delivered to the site;
- pipes are inspected in order to detect defects;
- the lashes are laid in a trench;
- Welding and joining works are performed;
- gas pipeline tests are being carried out;
- backfilling of the trench is being carried out.
Preparing a trench for laying a gas pipeline in advance with standards is not allowed. There should not be any stones and debris at its bottom. Pipes are welded in a whip outside the trench. This eliminates the possibility of leaks in the future. When lowering the lashes, they must not be allowed to hit the bottom and walls.
The assembly of gas pipelines in the winter season is allowed by standards. However, in this case, the trench should be dug up to unfrozen soil. On rocky sections, pipes are laid on a sand cushion. The thickness of the latter should be approximately 200 mm. This eliminates the risk of damage to the pipes due to contact with stones.
special instructions
Sometimes gas pipelines have to be pulled along problem areas. On landslide territories, as well as on soils subject to erosion, construction must be carried out below the boundary of possible destruction. Pipes pull at least 0.5 meters from the level of the sliding mirror.
Rules for the assembly of elevated systems
The requirements for laying gas pipelines of this type are as follows :
- above the ground, the gas pipeline should be located not lower than 2.2 m in the places of passage of people, 5 m - above the roads, 7.1 m - over the tram tracks, 7.3 m - in those places where trolleybuses travel;
- the distance between the fixed supports of the line should be equal to a maximum of 100 m with a pipe diameter of up to 30 cm, 200 m - up to 60 cm, 300 m - over 60 cm;
- Steel gas pipes intended for installation above the ground must have a wall thickness of at least 2 mm.
Gas distribution pipelines in small towns are often laid along supports. The distance between the latter directly depends on the diameter of the pipes. So, for Du-20, this indicator will be 2.5 m, Du-50 - 3.5 m, Du-100 - 7 m, etc.
What is a gas protection zone
Engineering systems of this variety are explosive structures. Therefore, in the immediate vicinity of them, no construction should be carried out. The sizes of security zones depend on the types of gas pipelines:
- high pressure category I (0.6-1.2 MPa) - 10 meters;
- high pressure category II (0.3-0.6 MPa) - 7 m;
- medium pressure (5-300 MPa) - 4 m;
- low pressure (up to 5 MPa) - 2 m.
The security zone of the LPG pipeline is usually 100 meters.
According to the standards, once a year the route is adjusted with the introduction of existing changes to the documentation. In order to mark the protection zone of the pipeline, special columns are used. Their location is prescribed at a distance of not more than 50 m from each other. Are indicated by columns and places of turn of the highway. At intersections with roads and bridges in the security zone, appropriate warning signs are installed. On the highway in such places signs are also provided prohibiting parking.
Laying gas pipelines indoors
In this case, certain safety standards must also be observed. A gas pipeline is laid in transit inside buildings on the external surfaces of the walls at a height of at least 1.5 meters from the floor. Sometimes pipes are pulled in channels covered by shields. The latter at the same time, according to the regulations, should be easily removable. Through the walls or floors, gas pipelines are laid in metal sleeves insulated with non-combustible material.
According to the regulations, it is forbidden to pull pipes:
- on door and window frames;
- transoms;
- platbands.
Wooden walls before installing gas equipment next to them should be insulated with asbestos-cement sheets. All joints of the internal gas pipeline are welded. It is allowed to make detachable only connections in places of installation of shutoff valves.
Steel pipes are commonly used to assemble internal systems. But sometimes copper is also used for this purpose. It is not allowed to use such highways only for transporting LPG.
The connection of the internal transit gas pipeline to the external one and its assembly should, according to the standards, be carried out only by specialists of a licensed company. After the installation of the system, its tests and acceptance are carried out with the signing of the corresponding document.