a structure for transporting gaseous fuels over long distances (hundreds or thousands of kilometers) from the point of extraction or production to the points of consumption.

Gas pipelines may be laid underground, on the surface, or on embankments. The pipelines in the European part of the USSR (in the zone of seasonal soil freezing) are usually laid underground. Elevated pipelines on supports—the so-called spiral type—are widely used in the northern regions. In permafrost areas gas pipelines are built up on embankments or are laid on the surface or underground. In certain instances, pipelines are mounted on supports or suspended from cables (over large ravines or rivers); they may also be laid across the bottoms of bodies of water (so-called sag pipes).

Corrosion insulation, cathode protection, and protective shielding are used to protect the pipes from internal or external corrosion.

The gas pressure in the main pipelines is maintained over long stretches by gas-compressor stations.

In the USSR the optimum parameters of gas pipelines are as follows: operating pressure, 5.5 meganewtons per sq m (MN/m²; a gas pipeline with an operating pressure of 7.5 MN/m² is under construction); compression ratio (maintained by the compressor station), 1.4-1.5; distance between adjacent compressor stations, approximately 100-120 km; unit rating of compressor plants, 5,000-10,000 kilowatts or more. The liquid (water, condensate, oil, and so on) formed in the pipeline during the transport of the gas is collected in condensate tanks.

Gas-distribution stations, at which the pressure is reduced to the level required for supplying consumers, are located at the terminal point of the main gas pipeline. Underground gas-storage facilities are constructed in the vicinity of large cities, and daily irregularities of consumption are partially covered by the use of gas tanks. Thin-walled pipes 720-1,420 mm in diameter are used in modern main pipelines in the USSR.

The first references to gas pipelines date to the beginning of the Common Era, when bamboo pipes were used for transmitting natural gas in China. Gas pipelines made of cast iron were first used in Europe in the late 18th century; in the 19th and 20th centuries they were replaced by steel pipes, which allow the transport of gas under much higher pressure than was possible with cast-iron pipes. The extraction of natural gas achieved its greatest scope in the USA in the early 20th century (20 billion cu m), where the total distance spanned by numerous short gas pipelines was 22,000 km (1918). In 1928-31, gas pipelines 800-1,500 km long and 508-660 mm in diameter were built in the USA.

Until 1941 the development of gas-pipeline transport in the USSR was characterized by the construction of small-diameter (100-250 mm) pipelines for the delivery of gas from deposits with relatively small supplies of natural and by-product natural gas. The first long-distance gas-supply pipeline was constructed in the USA in 1944 (the Tennessee gas pipeline). The diameter of this pipeline is approximately 600 mm, and the length of the main line is 3,300 km. In subsequent years large interdistrict systems of pipes 762-914 mm in diameter were created. In 1946-50 the first large gas pipelines were built in the USSR to deliver gas from the deposits in Saratov Oblast to Moscow and from the deposits in Ciscarpathia to Kiev and other cities in the Ukraine. The first main gas pipeline in the USSR was the Saratov-Moscow pipeline, 325 mm in diameter and 800 km long, which was put into operation in 1946. Larger pipelines were constructed later: Dashava-Kiev-Moscow (1,300 km), Serpukhov-Leningrad (813 km), Dashava-Minsk (665 km), Shebelinka-Belgorod-Kursk-Orel-Briansk (507 km), Saratov-Gorky-Cherepovets (1,188 km), and Krasnodar Krai-voroshilovgrad-Serpukhov (approximately 1,300 km). The largest gas-transport systems in the USSR are the double-line Bukhara-Ural system, with a total length of 4,503 km, constructed of pipes 1,020 mm in diameter and with an annual capacity of 21 billion cu m, and the Middle Asia-Central Zone double-line system, constructed of pipes 1,020 and 1,220 mm in diameter, with a total length of approximately 5,500 km and annual capacity of 25 billion cu m. The chief distinguishing feature of the construction of main gas pipelines in the USSR is the creation of a united system ringing the European USSR, which provides increased efficiency of the national economy and ensures continuity and reliability of gas supplies. The steady increase in the proportion of large-diameter gas pipelines (see Table 1) is another distinctive feature in the development of gas-pipeline transport in the USSR.

In 1967, pipes 1,220 mm in diameter were used extensively for the first time; these pipes were used in the Ukhta-Torzhok gas pipeline and are now being used in the second line of the Middle Asia-Central Zone gas pipeline, which is under construction.

A high degree of mechanization and the creation of new, highly efficient equipment and machinery permitted a sharp increase in the rate of pipeline construction. The Saratov-Moscow gas pipeline was built in 2½ years, the Dashava-Kiev pipeline in two years, and the Stavropol’-Moscow pipeline, which is approximately 1,000 km long and is constructed of pipe 720-820 mm in diameter, in less than two years. The first phase of the Bukhara-Ural gas pipeline, with a diameter of 1,020 mm and a length of 2,200 km, was built in two years, in spite of difficult natural conditions (desert and rocky ground); the first phase of the Middle Asia-Central Zone pipeline, 1,020 mm in diameter and 2,700 km long, was constructed over a period of 1½ years.

Proposals for a radical change in the technology of transporting gas over great distances, using pipes 2-2.5 m in diameter, have been developed in the USSR. The increase of pipe diameters to a specific optimum for the transport of gas provides a significant increase in the capacity of pipelines and reduces the specific capital expenditures, operating costs, and the use of metal. The preliminary technical and economic characteristics of transmitting gas through ultrahigh-capacity gas pipelines (the data for a gas pipeline 1,020 mm in diameter are taken as 1) are given in Table 2.

The construction of ultrahigh-capacity gas pipelines is characterized by high economic efficiency. The delivery of approximately 130 billion cu m of gas per year for the next seven or eight years from Tiumen’ Oblast and the Komi ASSR to the regions of the Central Zone, the Northwest, and the Urals through pipelines 1,220-1,420 mm in diameter would require the construction of seven or eight pipelines with a total length of approximately 25,000 km. This same quantity of gas could be transported through two ultrahigh-capacity gas pipelines, one with a diameter of 2.5 m and the other with a diameter of 2 m. The maximum pipe diameters in use are 1,067 mm in the USA and 1,420 mm in the USSR; average diameters are 410 mm in the USA and 674 mm in the USSR (1968). The construction of ultrahigh-capacity gas pipelines demands the organization of ultrahigh-capacity gas fields with annual gas outputs of 50-100 billion cu m. The daily well capacity must be 2-3 million cu m, rather than the current maximum capacity of 500,000-700,000 cu m. Projected designs for ultrahigh-capacity gas pipelines 2,020-2,520 mm in diameter call for the pipes to be manufactured of steel with walls 25-26 mm thick, ultimate strength of 550-600 MN/m², and guaranteed impact strength of not less than 0.3 MN/m² at a temperature of -40° C. The total length of main gas pipelines in the USSR is approximately 70,000 km (1970).