Gas Distribution System

a pipeline system (gas lines) for the transport of gas fuels and their distribution among consumers; the basic element of a populated area’s gas supply system.

Municipal gas distribution systems consist of gas pipelines for various purposes; gas reduction terminals, including municipal distribution points, municipal distribution stations, and individual pressure regulators that provide a constant pressure to pieces of equipment; and gas storage facilities (gas tanks) that compensate for irregular daily gas consumption (mainly for municipal and domestic purposes). Gas distribution systems are equipped with gas pressure meters, communication systems, warning systems, automatic controls, and shutoff fittings (such as shutoff valves, shutoff cocks, gate valves, and water seals) for disconnecting separate sections of the piping system or buildings during emergencies and repair work.

Gas distribution systems include gas distribution mains and gas service lines. Gas distribution mains are designed to deliver gas from the municipal distribution points and stations and from gas storage facilities to the areas of consumption. Gas service lines, through which gas is supplied directly to the consumers, go to buildings and structures. Inside buildings (structures) the gas is distributed by internal gas-piping systems. In municipal gas distribution systems, gas is delivered under a specified excess pressure. In low-pressure gas-piping systems, this pressure is up to 0.05 kilograms-force (kgf) per cm² (5 kilonewtons [kN] per m²); in medium-pressure gas-piping systems, from 0.05 to 3 kgf/cm² (5-300 kN/m²); and in high-pressure gas-piping systems, from 3 to 6 kgf/cm² (300-600 kN/m²) and from 6 to 12 kgf/cm² (600-1,200 kN/m²). Residential and public buildings and small public-utility enterprises are connected to low-pressure gas distribution systems; medium- and high-pressure (up to 6 kgf/cm²) systems feed low- and medium-pressure gas distribution pipelines through township distribution points and also feed gas pipelines of industrial and major public-utility enterprises through local distribution points and gas regulator installations; high-pressure systems (up to 12 kgf/cm²) are designed to deliver gas to storage facilities and major industrial enterprises.

The following systems are used for gas distribution: single-stage systems, which supply consumers with gas under a single pressure (for small populated areas); two-stage systems, which supply gas under two pressure combinations, either medium and low pressure or high (up to 6 kgf/cm²) and low pressure (in average-sized cities); three-stage systems, which supply gas under three pressures, high (up to 6 kgf/cm²), medium, and low (in large cities); and multistage systems, which supply gas under four pressures, high (up to 12 kgf/cm²), high (up to 6 kgf/cm²), medium, and low (in the largest cities). Seam and seamless pipes made from low-carbon and low-alloy steels are used for gas distribution system pipelines.

Gas distribution systems for populated areas are usually designed as closed ring or loop systems, in order to ensure uninterrupted gas supply during shutdowns of certain gas pipeline sections. All municipal gas distribution systems are generally buried underground. Aboveground gas-piping systems are used primarily on the property of industrial and public utility enterprises. Underground steel gas piping systems, and also main gas pipelines, are protected from soil corrosion and stray currents by anticorrosive insulation; electrical protection methods (cathode methods, grounding, protective liners) are also used. Gas pipeline diameters are determined according to hydraulic calculations that take into account all consumers at times of maximum gas consumption. The depth at which municipal gas piping systems are buried underground depends on the freezing level of the soil and the drying rate of the gas to be transported. According to regulations currently in effect, wet gas pipelines must be buried below the average depth of soil freezing, and dry gas pipelines may be located within the frozen ground zone at a distance of not less than 0.8 m from the top of the pipe to the surface of the ground (in order to protect the gas pipeline from damage by the weight of vehicles). Residential gas piping systems are installed with welded or threaded connection steel pipes; these piping systems consist of standpipes (risers), which transport gas in a vertical direction, usually for the entire height of the building, and apartment branch lines, which supply gas from the risers to the individual gas appliances. Gas risers are generally run in staircases, passageways, and kitchens; gas risers are not permitted in living spaces and toilets. Flanged and threaded fittings are used for connecting the gas appliances to the gas piping system.