What is a natural gas pipeline?

What is a natural gas pipeline?

Natural gas pipeline refers to the pipeline that transports natural gas (including associated gas from oil field production) from the mining or treatment plant to the urban gas distribution center or industrial enterprise users, also known as gas pipeline.
The use of natural gas pipelines to transport natural gas is a way of transporting large quantities of natural gas on land. Natural gas pipelines account for about half of the world’s pipelines.

Panoramaofthereceivingterminal Almeria - What is a natural gas pipeline?
What is natural gas?

Natural gas refers to all natural gases naturally occurring in nature, including gases formed by various natural processes in the atmosphere, hydrosphere, and lithosphere (including oilfield gas, gas field gas, mud volcanic gas, coalbed methane, and bio-generated gas).

W020170113584754575446 - What is a natural gas pipeline?
The long-established definition of “natural gas” is a narrow definition from the energy point of view, which refers to a mixture of hydrocarbons and non-hydrocarbon gases naturally present in the formation. In petroleum geology, it usually refers to oil field gas and gas field gas. Its composition is dominated by hydrocarbons and contains non-hydrocarbon gases.
Natural gas is contained in underground porous rock layers, including oilfield gas, gas field gas, coalbed methane, mud volcanic gas and bio-generated gas, and a small amount of coal seams. It is a premium fuel and chemical raw material.
The main use of natural gas is fuel, which can produce carbon black, chemicals and liquefied petroleum gas. Propane and butane produced from natural gas are important raw materials for modern industry. Natural gas is mainly composed of a mixture of gaseous low molecular hydrocarbons and non-hydrocarbon gases.
Mainly composed of methane (85%) and a small amount of ethane (9%), propane (3%), nitrogen (2%) and butane (1%). Also known as “biogas.” It is mainly used as a fuel and is also used as a raw material for the production of chemicals such as acetaldehyde, acetylene, ammonia, carbon black, ethanol, formaldehyde, hydrocarbon fuels, hydrogenated oils, methanol, nitric acid, syngas and vinyl chloride. Natural gas is compressed into liquid for storage and transportation. Coal miners, nitric acid producers, power plant workers, organic chemical synthesizers, gas users, petroleum refiners, etc. have the opportunity to contact this product. Mainly through the respiratory tract into the human body. It is a simple asphyxiating gas. When the concentration is high, the hypoxia is caused by the replacement of air, resulting in shortness of breath and loss of consciousness; in severe cases, suffocation may occur due to hypoxemia. High pressure natural gas can cause frostbite. Incomplete combustion produces carbon monoxide.
Natural gas is a general term for hydrocarbon-based mixed gas existing in underground rock reservoirs. Its specific gravity is about 0.65, lighter than air, and it is colorless, odorless and non-toxic.
Natural gas is mainly composed of alkanes, of which methane is the majority, and a small amount of ethane, propane and butane, in addition to hydrogen sulfide, carbon dioxide, nitrogen and water, and a small amount of carbon monoxide and traces of rare gases such as helium and argon. . Natural gas is added to the natural gas to add odor to the natural gas before it is sent to the end user, in order to facilitate leak detection, and to use mercaptan, tetrahydrothiophene, and the like.
Natural gas is insoluble in water, with a density of 0.7174 kg/Nm3, a relative density (water) of 0.45 (liquefaction), a burning point (°C) of 650, and an explosion limit (V%) of 5-15. Under standard conditions, methane to butane is present in a gaseous state, and above pentane is a liquid. Methane is the shortest and lightest hydrocarbon molecule.
Organic sulfides and hydrogen sulfide (H2S) are common impurities that must be removed beforehand in most natural gas applications. Natural gas containing more sulfur impurities is described in the English terminology as “sour”.
The calorific value of natural gas per cubic combustion is 8,000 kcal to 8500 kcal. The calorific value of combustion per kilogram of liquefied gas is 11,000 kcal. The specific gravity of the gaseous liquefied gas is 0.55. The combustion heat value per cubic liquefied gas is 25,200 kcal. Each bottle of liquefied gas weighs 14.5 kg and has a total calorific value of 159,500 kcal, which is equivalent to the calorific value of 20 cubic meters of natural gas.

Methane combustion equation

  • Complete combustion: CH4+2O2===CO2+2H2O (reaction conditions are ignited)
  • Methane + oxygen → carbon dioxide + water vapor
  • Incomplete combustion: 2CH4+3O2=2CO+4H2O
  • Methane + oxygen → carbon monoxide + water vapor

Unit of measurement

  • Kilowatt hours (kw·h) or joules (J)
  • Gas station sales unit: CNG yuan / cubic meter (yuan / m3), LNG ** yuan / kg

Structure of natural gas pipeline
The gas pipeline is assembled by a single pipe connected one by one.
Modern gas collection pipes and gas pipelines are made of steel pipes connected by electric welding. The steel pipe has a variety of seamless pipes, spiral seam pipes and straight seam pipes. The seamless pipes are suitable for pipes with a pipe diameter of 529 mm or less, and the spiral seam pipes and straight seam pipes are suitable for large diameter pipes. The cross-sectional structure of the pipe of the gathering pipeline is complicated by the inner coating-steel pipe-outer insulation layer-insulation (cooling) layer; the simple one is only the steel pipe and the outer insulation layer, while the inner wall coating and the heat preservation (cold insulation) layer are both considered The gas transmission process is further determined.
Natural gas pipeline material
Steel pipes are the main material of pipes. Natural gas transmission steel pipe is a special metallurgical product formed by deep processing of the plate (belt). The structural form of pipeline steel, due to the difference in process technology, there are certain differences in the pipeline steel produced by various manufacturers. In the 1960s, X52 steel grade was generally adopted, X60 and X65 steel grades were adopted in the 1970s, and X70 steel was mainly used in the 80-90s. X80 steel has been used in gas pipelines in some foreign countries. With the continuous development of pipeline steel research, Canada and other countries have laid the test section of X100 and X120 pipeline steel. In China, the X80 grade pipeline steel was used for the test section of 7.71km for the first time in the pipeline project of Suining. The 2,484km West-East Gas Pipeline 2 pipelines all use X80 steel grade pipe steel with a diameter of 1219mm, which will increase the gas transmission pressure to 12Mpa. In general, X80 steel is a ferrite and bainite duplex structure, X100 pipe steel is a bainite structure, and X120 pipe steel is ultra-low carbon bainite and martensite. For natural gas pipelines, strength, toughness and weldability are the three most basic quality control indicators.

Characteristics of natural gas pipelines

  1. The gas pipeline system is a continuous closed conveyor system.
  2. Natural gas is under pressure from transportation and storage to user use.
  3. Due to the small specific gravity of the natural gas delivered, the static head has a much smaller impact than the liquid. When the design height difference is less than 200 meters, the static head is negligible and the line is hardly restricted by the longitudinal terrain.
  4. There is no water hammer hazard in the liquid pipeline.
  5. When an accident occurs, it is harmful and has a wide range. Once the pipeline is broken, the release energy is large, the tearing length is long, and the discharged natural gas encounters an open flame, and it is easy to cause a fire.

Advantages of natural gas pipeline transportation
Natural gas pipeline transportation has low transportation cost, small land occupation, fast construction, large oil and gas transportation volume, high safety performance, low transportation loss, no “three wastes” emission, low risk of leakage, low environmental pollution, and little impact on bad weather. The equipment has small maintenance, easy management, and easy remote centralized monitoring.

Working pressure for long-distance oil and gas pipeline
Working pressure and diameter of oil and gas pipelines, are first identified in pipeline design framework technical parameters.
Working pressure directly determine the number of pumping stations and compressor stations, steel consumption in the power station unit and piping. Working pressure on the economy and security of the pipeline project is the first. Working pressure is an important part of the design of oil and gas pipelines, the technical and economic conditions of its great influence on the pipeline, the pipeline operating pressure is not too high; optimum working pressure gas pipeline and gas pipeline construction investment and operating costs related to; generally, the high pressure tends to work best value.
The total energy consumption depends on the oil pipeline transportation, total pressure consumption (assuming that the pipeline is located in the ground) and oil unit efficiency , independent of the size and pumping stations working pressure, working pressure pipelines and pipeline operating expenses not directly related, so the diameter is ok, work stress affects only tube road construction investment. Due to work pressure determines the number of steel consumption pumping stations and pipelines. Working pressure construction investment and a great influence on gas pipeline operating expenses. Best working pressure gas pipeline is much higher than the working pressure of the pipeline. Best job stress affect pipeline many factors, such as price pressures and pipe gas stations, etc., but the most important is the gas volume, diameter and strength of the steel pipe. Large gas pipelines at higher operating pressure, the amount of energy required to undertake gas pipeline smaller diameter. In other words, the higher working pressure (optimal operating pressure) can obtain better economic benefits for the gas pipeline project. This is also the reason for the gas pipeline to higher working pressure of development. Currently, high-strength steel pipe emerging, more pipelines to improve the working pressure.

Gas pipeline internal coating
Gas pipeline coating technology is a certain thickness of the pipe wall spray epoxy, not only avoid acidic gases in the transport pipe wall subject to corrosion, but also to prevent inclusion of other contaminants in the gas stream impurities deposited on the etched surface of the pipe wall side , which prevents the actual flow area reduction pipeline, reducing pipeline transmission capacity and reducing the energy consumption of gas pipelines are two ways: optimized at the design stage pipeline diameter, working pressure and pressure ratio choice and optimization of compressor stations settings, and selection of the host device; reduce friction losses gas pipeline, which is required when reducing the gas pressure. Now reduces gas pipeline friction loss is the only way to cover the inner surface of the pipe inner coating layer drag reduction. Inner pipe wall covered with drag-reducing coating, its most important role is to reduce hydraulic friction coefficient, but also reduces the gas when the gas pressure required. That is, the drag reduction effect of the coating on the inner diameter of the stated conditions and the gas volume, reducing the pipe line gas power; or the entire pipeline has been set the total power, increase the amount of gas pipeline . For large diameter gas pipeline, its effectiveness is very large.
Pipe coating technology, the main function of drag reduction, corrosion. Therefore, drag reduction performance coating composition within the basic requirements are: adhesion strength, permeability, abrasion resistance, pressure resistance, heat resistance, chemical stability and corrosion resistance and glossiness.
There are many substances in the coating composition, film-forming material can be divided, pigments, additives and solvents four categories, which film material is essential. To be able to form a good performance of the pipe wall covering layer of coating composition must be chosen properly, formulation science and reasonable. Domestic chemical industry to develop a major film by coating the coating material classification, but also in the practical application covering layer forming at whether a chemical reaction, the protective effect of the coating, and the coating of the physical form of classification.
Construction of the basic procedures within the coating:
Preheat pipeline-Surface treatment-Dust-End of the tape-Airless spray-Accelerate the curing-Test-Pile up((Storage to be transported).
Long-distance gas internal coating drag reduction technology has a good technical and economic nature. Drag reduction for the purpose of natural gas in the inner coating technology is a great promotional value of the technology. Technology compared with coated inner coating technology is relatively simple, that a single species, space is limited to the tube, without heating, construction conditions easier to control.
Gas pipeline testing technology
The development direction of the gas pipeline testing technology
Gas pipeline usually been in running from within and outside environmental corrosion, internal corrosion mainly by the transmission medium, pipe joint effusion, dirt and pipeline stress formed; external corrosion is usually due to failure of the coating, failure to produce.
The internal corrosion commonly used love pipes, corrosion inhibitor and other means to deal with in recent years with the strengthening of the pipeline owners of the pipeline operation and management, and the stringent requirements of the transmission medium, internal corrosion in large part to get control. At home and abroad oil pipeline corrosion control main development direction of the outer anti-corrosion, pipeline inspection focusing on coating defects and pipe defects due to external corrosion caused by. In recent years, with the widespread popularity of computer technology and applications, domestic and international testing technology has been rapid development, pipeline inspection technology gradually formed pipe internal and external detection technology (coating detection, intelligent detection) two branches. Under normal circumstances, the coating is damaged, the failure at the bottom of the pipeline is also subject to corrosion, the pipeline external detection techniques aim is to detect the coating and cathodic protection on the basis of the validity of, to achieve the purpose of detecting the tubular body corrosion defects by digging detected, and for The most current layout North The condition is detected in the pipeline is very effective. In-line inspection technology used to discover both inside and outside the pipe corrosion, local deformation and weld cracks and other defects, but also indirectly determine the integrity of the coating.
Outside of the pipe detection technology
Buried pipeline commonly used coating and the power-law protection (CP) protection system consisting of the combined effects of external corrosion control plays a complementary role of these two methods: the coating is cathodic protection that is economical and effective, and cathodic protection also coating to pinholes or injury under control. The method has been recognized as the best protection approach and has been widely used for corrosion control of buried pipelines. Coating detection technology is in pipeline excavation under the premise of, use of special equipment on the ground non-contact coating comprehensive performance testing, scientific, accurate and economical aging and damage the coating defect positioning, the size of the defect classification statistics, a comprehensive evaluation of defect size, number and proposed corrective action plan to guide the pipeline owners grasp the pipeline coating condition and maintenance, and practical to ensure the integrity of the coating and integrity. Domestic implementation of the outside of the pipe detection technology began in the mid-1980s, the detection methods include standard pipe / ground-sensing Pearson (Pearson) the coated insulation resistance test tube current test. The test results an important role in the overall evaluation of the coating to the accurate positioning, but the defect, reasonable guidance overhaul there was still a big gap. In recent years, the World Bank loans, and exchanges with foreign pipeline company, outside of the pipe testing equipment due to the price is relatively cheap, more convenient operation, the foreign pipeline outside the technology has been widely used in Petroleum Pipe Coating detection, currently the outside of the pipe detection technology basically reached the advanced level of developed countries, which is widely used in practical work outside the detection technology include: standard pipe / ground-sensing, Pearson detection, fine-pitch potential test, the audience current multi-frequency test, DC gradient test.
In-line inspection technology
In-line inspection technology is a variety of non-destructive testing (NDT) equipment on the Island pig (PIG), originally used as a purge of non-smart changed information collection, processing, storage and other functions of intelligent pipeline defect detection (SMART PIG), through the movement of the pig in the pipeline to achieve the purpose of detecting pipeline defects. As early as 1965 U.S. Tuboscopc had the magnetic flux leakage (MFL) non-destructive testing (NDT) technology successfully applied to the inside of the oil pipeline detection, followed by other non-destructive testing techniques have also generated, and try to find the broad application prospects. Famous foreign monitoring company by the United States Tuboscopc GE PII, the UK’s British Gas, Germany Pipetronix, Corrpro Canada, and its products have basically reached a series and diversification. Within the detector can be divided according to the functions used to detect pipeline geometry deformation diameter measurement for pipeline leak detection, magnetic flux leakage detector for detection of volumetric defects due to corrosion, used in crack plane defect detection vortex detector, ultrasonic detector, and based on the elastic shear wave crack detection equipment.

Internal coating pipes

Internal coating pipes - What is a natural gas pipeline?
pipe internal coating

Using epoxy powder coating is for 30 years of history in a foreign country due to the wide range of sources of raw materials, production methods are simple, cheap, good performance, which do not pollute the environment and long service life, so far it is a good anti-corrosion coatings.

Internal and external 2 and 3 layer coating - What is a natural gas pipeline?

Internal and external 2 and 3- layer coating is applied for oil and gas pipelines, product pipelines and fire extinguishing systems

Use of pipes with internal coating provides an ecological safety, a reliability, keeps the good quality of drinking water in pipeline systems during the long term operation.

Petroleum Institute of Construction Technology in China for the oil field pipeline corrosion problems and successfully develop the anti-corrosion coating of epoxy powder to fill the blank of the domestic pipeline anti-corrosion powder coating.

The paint coating has excellent chemical resistance, good mechanical properties, high electrical insulation properties and good toughness. Corrosion tests predict coating life, the conditions intact Chu apply the paint to do the inner coating of oil, gas and water pipes, the life expectancy of up to l5 years; do sewage and mixed water injection pipeline within the coating, life up to 5 to 7 years. The construction method using the pipeline industry, the most widely used static thermal spraying method. According to the data reported, due to the transmission medium, the thickness of the coating of epoxy powder coating requirements are also different. Domestic oil, gas, water and sewage, etc. containing certain corrosive media, anti-corrosion pipe is the best thick coating. Electrostatic heat till coated thick coating, spraying a coating thickness of up to 250 ~ 350/an maximum thickness of up to 500, ~ ‘n. Electrostatic Powder the moraine coated is a surface treatment of the solid powder, it has a simple, easy to operate equipment, process, free from the workpiece size limit. 
Inner surface heat-resistant paints and coatings 
The technology is the surface heat-resistant paint coating that mixed epoxy resin main agent and epoxy resin curing agent in the steel pipe (each about 5.5m), natural drying a certain period of time, more than 6O ℃ warm water or 60 ℃ or more hot air into the tube, forced drying, more than three hours to complete the steel pipe coating. The technology is mainly applied to water pipelines and transmission and hot water pipe internal coated first surface treatment on the pipe wall, and then use the compressor by the pressure of air or nitrogen, Pressure between the resistance and the two applicator thermal coating in the pipe wall to form a uniform coating. Coating must 6O ° C more than warm water or 60 “C, hot air above the mandatory drying and natural drying is heat resistant to dissolution performance decreased significantly. 
Epoxy resin latex cement mortar lining 
Epoxy resin latex cement mortar lining in the steel tube surface first coated with epoxy cement water-based paint, to form the undercoat, and then based on this coating the lining. The use of materials is containing epoxy resin latex cement mortar. Colloidal silicon dioxide is added in the cement mortar. Cement water-based coatings and cement mortar contain ionic latex (a hydrocarbon solvent containing 5 to 8 sugars). The lining of steel pipes, except for sewage and water pipelines is also apply to oil, gas and steam pipelines. In order to get a solid lining, pipe lining before, the surface must be shot peening, shot peening is divided into dry and wet shot peening, if both methods are not adopted, can also be used to pickling.

Oil and gas pipeline anti-rust varnish
Analysis on production process and performance of gas pipeline, which pointed out that the main reason for the lack of oil pipeline anti-rust performance and proposed oil and gas pipeline coating process improvement, and the correct selection of a rust-proof varnish in order to achieve long-lasting anti-corrosion effect.
The basic requirements of the oil and gas pipeline rust layer
The production process of the oil and gas pipeline, the long-distance transport conditions and open dumps time, rust varnish should have the following properties: good construction performance, security, environmental protection, quick drying; bright, transparent film, does not cover Coding ID, do not cover up the steel pipe surface rusty state; oil pipeline to withstand wind, sun, rain and other environmental conditions, anti-rust layer should have good weather resistance; impact, bumps and impact damage during handling and transport of the oil pipeline, there factor, anti-rust layer should have good impact resistance; the operation of shipping, hot and humid zones, anti-rust layer should have good moisture resistance, salt spray resistance; in the cold region in winter and summer desert regions, the ambient temperature -30 to 60 ° C, anti-rust layer should have good temperature variability.
Coated tube is a preservative tube, spray anti-corrosion coatings prepared in the ordinary oil and gas pipeline corrosion preventive coating are strong. Compared with the coating tubing spraying process, the coating process of the anti-rust layer of the oil pipeline is far too simple: the construction of the steel pipe surface pre-treatment; only spray an anti-rust paint, coating thickness is insufficient and uneven; coating drying insufficient coating strength is not enough, easy to destroy; the appearance of the coating thickness, leakage, adhesion did not examine the control.
It can be seen: the anti-rust layer of the oil and gas pipeline to improve performance, optimize the production process, it is necessary to ensure that the coating quality.

Current Status of Drag Reduction and Transmission Technology for Gas Pipeline
One way to effectively reduce the coefficient of friction is to apply an inner coating to the inner wall of the pipe to obtain a relatively smooth inner surface. The drag reduction of natural gas pipelines is currently known and applied by chemical methods, namely the inner coating technology. A typical example of the application of natural gas pipeline drag reducer (DRA) is Chevron Petroleum Technology Co., a natural gas drag reducing agent on a 8km long and 152mm diameter gas pipeline in the Gulf of Mexico. Field Test. The results show that the output can be increased by 10% to 15%, and the maximum pressure is reduced by 20%. The main chemical component of such a drag reducer is a polyamide base. Through the injection system, the drag reducing agent is periodically injected into the natural gas pipeline at a certain concentration, and the drag reducing agent can form a smooth protective film on the inner surface of the pipeline, and the thin film can significantly reduce the conveying friction. However, the natural gas pipeline drag reducer developed by Chevron has a limited service life in the tube. After a certain period of time, the film will fall off by itself, and the drag reduction efficiency will also decrease. Field tests show that the effective period of DRA can reach 400h.
In the technical research of reducing the airflow resistance in the gas pipeline, France has used the laser method to form a pulse flow in researching ways to overcome the internal pressure loss of the gas pipeline. They found that the hydraulic roughness of a single pipe section is usually about 20 μm. However, in production, due to the complex composition of the fluid, the roughness may exceed 50 μm. The resistance coefficient will be relative to the smooth wall of the high Reynolds number. Increase by more than 40%. The newly retrieved petroleum science literature shows that the French Petroleum Institute (IFP) is evaluating and studying the aerodynamic properties associated with this technology. The pressure loss of the gas pipeline, especially due to the roughness of the pipe wall, strongly affects the drag coefficient, resulting in an increase in the Reynolds number, which in turn causes relatively high operating costs.
In summary, one way to effectively reduce the coefficient of friction is to apply an inner coating to the inner wall of the pipe to obtain a relatively smooth inner surface. Other techniques can be used to further reduce friction due to conditions below the desired smooth surface of the tube wall. The following are some of the advanced technologies available:

  1. A surface formed by a special structure (a spiral structure surface);
  2. Porous / permeable coating;
  3. Special coating materials;
  4. Applying grease to the pipe wall;
  5. Flexible coating;
  6. Form a pulsed stream;
  7. Make it fluid again;
  8. Particle injection.

France’s research in this area of expertise, systematic, comprehensive and fruitful, represents the most advanced level in the world today. According to the information. The country uses a laser device to generate a pulsed stream. But cost is a big challenge. So far, no physical, low-cost drag reduction transmission method has been found that has been put into use.
Inspired by the “pulse flow of gas pipelines can reduce the friction of the pipe wall”, China’s petroleum researchers are experimenting with the development of pipeline pulse flow drag reduction and transmission technology, and have made significant progress in this technology. The bypass test and the main gas pipeline test have been completed. On-site industrial tests have shown that the pulse flow drag reduction and increaser has a very good effect of reducing drag and loss on the gas pipeline (same as the chemical transmission reduction and transmission technology). The pipeline extender is designed according to the aerodynamic theory. It draws on Professor Wu Yunpeng’s principle of efficient pulse wave transmission and Professor Liao Zhenfang’s microscopic vibration drag reduction theory. It is only necessary to install the pipeline feeder at the appropriate position of the gas pipeline. Without adding any additional auxiliary devices, depending on the special geometry of the feeder’s own chamber and specific boundary conditions, the continuous gas flow can be converted into a pulsed flow, and the amplitude of the outlet pressure of the generator is also increased. The magnitude of the outlet pressure can be increased by 10% to 35%. Under the condition of not changing the diameter of the pipeline and installing the booster station, the pipeline feeder can significantly increase the gas transmission volume of the pipeline, and the manufacturing cost of the feeder is low, no moving parts, reliable operation, and easy assembly and disassembly. Simpler and cheaper technology makes it possible to get all natural gas pipelines up and running as quickly as possible. Therefore, the promotion and application of this technology is of high value, which is what it means.
Increase rate of natural gas pipeline after applying internal coating
Through the research on the mechanism of drag reduction and transmission of oil and gas pipelines, the drag reduction technology of oil and gas pipelines can be classified. Various resistance reduction and transmission measures can be divided into two categories, one is to reduce the viscosity or equivalent viscosity of the fluid at du/dry, for example, heating, adding pour point depressant or viscosity reducer, emulsification, suspension, magnetization, low Mucus ring, etc., specifically: viscosity reduction transport (heating, adding pour point depressant, heat treatment, adding viscosity reducer, dewaxing modification*, cracking modification*, microbial degradation*, magnetic treatment*, pressure treatment*, microwave treatment *, ultrasonic treatment *, etc.), dilute transport (dilution, emulsification, suspension, gas saturation *, etc.), low mucus ring transport (water ring, thin oil ring *); the other is to reduce the additional stress of turbulence, especially Reduce the turbulent additional stress near the pipe wall (ie, suppress radial pulsation), for example, adding a drag reducing agent, applying an inner coating and an elastic film (ie, injecting a flexible single long-chain polymer, forming an elastic wall), and injecting a high polymer Things* and so on. Other drag reduction principles, such as increasing pipe diameter, oil pipelines include pig cleaning, large-discharge flushing, avoiding the peak temperature range of waxing, and natural gas pipelines including pig cleaning, dry natural gas, and chemical addition. Agent, blood pressure. The wall modification of the oil pipeline*, the mechanism belongs to the sliding of the fluid against the wall surface. Therefore, the transportation process can be divided into four categories: viscosity reduction and drag reduction, suppression of radial pulsation and drag reduction, wall modification and drag reduction, and reduction of wall deposits. For the natural gas pipeline, the drag reduction mechanism of “forming the pulse flow*” belongs to the second category, that is, the purpose of reducing the resistance is achieved by suppressing the radial pulsation near the tube wall. (Note: * is a drag reduction technology that is still in the theoretical research, indoor test or field test stage.)
Generally, the absolute equivalent roughness of the bare tube is 20 to 50 μm, and the absolute equivalent roughness after the application of the undercoat layer is 5 to 10 μm, and the average value (δ=35 μm, δ coating = 7 μm) is taken, and the inner coating of the natural gas pipeline can be calculated. The rate of increase after the layer. Through the study of the increase rate of natural gas pipelines, it is found that the change of the increase rate with the diameter of the pipe and the Reynolds number has the following law: for the same pipe, the increase rate increases with the increase of Reynolds number or output; when the Reynolds number is the same The increase rate increases with the decrease of pipe diameter; for large pipe diameter (2r0≥500mm) natural gas pipeline, when Re<105, the increase rate is less than 1%. In the range of 5 × 105 < Re < 5 × 107, the increase rate significantly increases as Re increases. Generally, the Reynolds number of the natural gas main pipeline is 106-107, and the transmission rate after the inner coating is generally 4% to 8%. For natural gas pipelines with a diameter of 500-1400 mm, the increase rate is about 2% to 11%. The downstream V-shaped groove surface has a significant drag reduction effect. This was discovered by experiments by Walsh et al. at the NASA Langley Research Center in the 1960s. According to recent literature, the hydraulics laboratory of the Oil and Gas Storage and Transportation Engineering Center of Jiangsu Institute of Technology, China, with the help of hot wire anemometer (HWA) and laser Doppler (LDV), respectively, on the V-shaped groove surface shape parameters (height, spacing, clip) Angle) and the turbulent boundary layer turbulence characteristics, burst characteristics, frequency and strip structure have been valuable research. They used the PIV experimental technique to achieve a maximum 5.89% drag reduction rate. In the field test preliminary test, the pulse flow feeder has an increase rate of about 2.4% and a drag reduction rate of about 5.0%. This is a good drag reduction effect and is a surprise discovery that is significant.
 In summary, interface processing drag reduction is an emerging cutting-edge technology. Based on the principle of bionics and related advanced theories, research and development of interface drag reduction technology to reduce energy consumption and improve efficiency has a good development prospect. Interface drag reduction technology is also one of the new trends in international R&D and application of new technologies. Strengthening and attaching importance to the research of interface drag reduction technology has an important role and significance. Widely adopting the inner coating drag reduction technology to improve the conveying capacity is one of the characteristics of the current development of foreign gas pipeline technology.
What are the risks of long-distance natural gas pipelines?
The construction and construction of the long-distance natural gas pipeline system is to achieve the purpose of long-distance pipeline transportation of natural gas, so that users along the line can obtain the required gas volume to meet the needs of users. The procedures for pipeline construction are complicated. Long-distance pipeline systems are generally buried pipelines. Pipe trenches need to be dug. For special pipeline systems such as rivers and residential areas, optimization design is needed to ensure the quality of pipeline construction and to extend pipeline use. Life expectancy to ensure safe and smooth delivery of natural gas. The key technology is the welding technical measures of the pipeline. According to the conveying distance of the long-distance pipeline, the welding pipeline forms a continuous hydraulic system to ensure the quality of the welding construction, and the welding quality is checked to avoid welding defects. The cathodic protection design of the pipeline system is carried out to reduce the corrosion of the pipeline. According to the requirements of the design drawings, the pipe valve, elbow and other equipment are connected to realize the effect of the distribution and meet the needs of long-distance pipeline transportation of natural gas.

Risk identification of long-distance natural gas pipelines

(1) The nature of the transport of natural gas. The risk we refer to refers to the combination of the possibility and consequences of a specific hazard event. The root cause and form of the hazard hazard are identified through hazard identification, and reasonable prevention and control measures are formulated according to the nature. The medium transported by the pipeline is natural gas. The main component of natural gas is methane, which is flammable. Once the pipeline leaks, it will spread rapidly and easily cause explosion and combustion. When the natural gas content of the air reaches a certain proportion, it will explode in the fire, causing casualties and property losses.
(2) The main form of expression.

  • First, an irresistible natural disaster occurs. Natural gas encounters earthquakes, mudslides, ice, floods, landslides, etc. during the transportation process, which damages the body of the natural gas pipeline, causing the pipeline to break or be damaged, resulting in natural gas leakage. This hazard is huge and unpredictable. We need to fully understand the local natural conditions and weather conditions in construction and pipeline operations, and familiar with the characteristics of soil vegetation, water protection facilities, weather changes, and minimize the impact of natural disasters.
  • Second, third-party damage, man-made unconscious destruction, theft, close fire, illegal construction, terrorist attacks and other pipeline accidents. By observing the living and production environment around the station and the line to determine whether there are risk factors that endanger the station and the line.
  • The third is illegal operation. Due to the nature of pipeline construction, high risk such as restricted space, excavation work, high-altitude operation, mobile hoisting operation, pipeline opening, temporary power consumption, hot work, etc., due to the characteristics of field construction, The impact of various extreme climatic conditions and complex geological conditions on safety is almost always present. The violation of regulations and illegal operation of personnel may cause major accidents in pipelines and stations. Through safety production rules and regulations to check whether there are dangers in various operational behaviors.
  • Fourth, corrosion, corrosion of pipelines, equipment, and installations in the surrounding environment may cause large-scale leakage of natural gas pipelines, station natural gas, and fire and explosion accidents. Determine the risk of potential hazards by regularly checking the wall thickness of the pressure vessel equipment and piping and the external corrosion of the equipment.

Six natural gas pipelines across the Mediterranean

The Mediterranean Sea is the largest land sea in the world. It is about 4,000 kilometers long from east to west, about 1,800 kilometers wide from north to south, and covers an area of about 2.5 million square kilometers. Its north bank is a relatively developed European region with a large demand for natural gas. In 2014, its consumption was 109.6 billion cubic meters, and its import volume was 414.1 billion cubic meters. The South Bank is a relatively abundant natural gas region in Africa, with a production of 202.6 billion cubic meters in 2014. The export volume is 82.8 billion cubic meters. At present, four submarine natural gas pipelines such as Greenstream, MEG, Medgaz and TransMed have been opened between the two continents, and two natural gas pipelines such as GALSI and TransSah are planned. After the completion of the above various pipelines, the annual gas transmission capacity will reach 101.2 billion cubic meters per year, which is beneficial to the export of natural gas resources in Africa and the safety of energy supply in southern Europe.
1. Green stream pipeline
The pipeline is the longest natural gas pipeline through the Mediterranean Sea. It starts from the first station of Mellitah in Libya and travels north to the Mediterranean Sea. It stops at the end of Gela, Siri, Italy, and is connected to other natural gas pipelines in Italy. The pipeline is 516 kilometers long and the depth of the seabed is 1127. The meter has a diameter of 813 mm, a design pressure of 21.2 MPa, and a designed output of 11 billion cubic meters per year. The gas source is mainly from the Bahr Essalam offshore gas field in Libya and the Wafa gas field near the Algerian border. It is connected to the first stop of Mellitah via the Bahr Essalam-Mellitah pipeline and the Wafa-Mellitah pipeline. The length of the gas source pipeline is 530 km and 110 km respectively.
The pipeline project has a total investment of approximately US$6.6 billion and is constructed and operated by Greenstream BV (share ratio 50:50), a joint venture between Italy’s Eni and Libyan NOC. The pipeline started construction in 2003 and was completed and put into operation in October 2004.
2. Algeria-Europe Gas pipeline
The Algerian-European natural gas pipeline originates from the HassiR’Mel gas field in Algeria, westward through Morocco, north across the Mediterranean Sea from the port of Tangier, from the port of Tarifa in Spain, to Córdoba in Andalusia, and to Spain and The Portuguese natural gas pipeline network is connected, with a total length of 1,620 kilometers and a designed transmission capacity of 12 billion cubic meters per year.
The pipeline project has a total investment of about US$2.3 billion and consists of five parts: Algeria has a section length of 515 km and a diameter of 1219 mm. It is operated by Sonatrach of Algeria; Morocco has a section of 522 km and a diameter of 1219 mm. The assets are owned by the Moroccan National Government. All, operated by a joint venture between Sagane, Transgas and SNPP; the Mediterranean cross section is 45 km long and has a diameter of 559 mm, which is jointly owned by Enagas of Spain, Transgas of Morocco and the National Government of Morocco; It is 269 kilometers long and has a diameter of 1219 mm. It is operated by Enagas of Spain. The Portuguese branch is also 269 kilometers long and has a diameter of 711 mm. It is operated by Transgas of Portugal. The pipeline started construction in October 1994 and was completed and put into operation in December 1996.
3. Medgaz pipeline
The pipeline originates from the HassiR’Mel gas field in Algeria, crosses the Mediterranean Sea in the port of Benisaf, and flows from Almeria, Spain, and is connected to the existing natural gas pipeline network in Spain, with a total length of 757 km, of which the land pipeline is 547 km long and the pipe The diameter is 1219 mm, the submarine pipeline is 210 km, the pipe diameter is 610 mm, and the designed transmission volume is 8 billion cubic meters per year.
The pipeline project has a total investment of approximately 900 million Euros and is operated by a joint venture between Sonarach of Algeria, CEPSA of Spain, Iberdrola, Endesa and GasdeFrance of France, with a stock ratio of 36:20:20:12:12. The project started construction in March 2008 and was completed and put into production in March 2011.
4. Trans-Mediterranean Pipeline
The pipeline originates from the HassiR’Mel gas field in Algeria, heading northeast to Tunisia, crossing the Mediterranean Sicily Channel on the Kabyan Peninsula, landing from Sicily, Italy, and then crossing the Strait of Messina to the north, to the northern part of Italy. The total length is 2,485 kilometers and the designed transmission volume is 30.2 billion cubic meters per year.
The pipeline consists of the following six parts: Algeria has a section length of 550 km and a diameter of 1219 mm. It is double-pipe laid and operated by Sonatrach of Algeria; the section of Tunisia is 370 km long and the diameter of the pipe is 1219 mm. The double pipe is laid by the Italian TTPC. The company is responsible for operations, but the pipeline assets are owned by Sutugat, Tunisia, and collects 5.25%~6.75% of the total value of transit natural gas as transit fee; the pipeline spanning the Sicilian Strait is 155 km long, with a diameter of 508 mm, and three pipes are laid by Sonatrach of Algeria It is operated by TMPC, a joint venture company of Italy’s Eni company; it is 340 km long in Sicily, Italy, with a diameter of 1219 mm, double pipe laying; 15 km long across the Strait of Messina, with a diameter of 660 mm, double pipe laying; northern Italy The section is 1055 kilometers long and has a diameter of 1067 mm. All pipelines in Italy are operated by SnamReteGas, Italy.
The pipeline was started in 1978. In 1983, a single pipeline was built and ventilated. In 1994, the second pipeline was completed and put into operation.
5. Algeria-Italy Natural Gas Pipeline (GALSI)
The GALSI gas pipeline starts from the HassiR’Mel gas field in Algeria, parallels the TransMed gas pipeline to the Tunisian border, is laid north to Calais, crosses the Mediterranean Sea to the Port of Porto, Sardinia, and is laid north to Olbia, the second time. After crossing the Mediterranean Sea, it reaches Piombino, Tuscany, northern Italy. The total length of the pipeline is 1,505 kilometers and the designed output is 10 billion cubic meters per year. The Algeria section is 640 km long, with a diameter of 1219 mm and a design pressure of 7.5 MPa. The first crossing of the Mediterranean section is 285 km long, with a diameter of 660 mm, a seabed depth of 2885 m and a design pressure of 18.2 MPa. The length of the territory is Sardinia. 300 km, diameter 1219 mm, design pressure 7.5 MPa; the second crossing of the Mediterranean section is 280 km long, diameter 559 mm, design pressure 20 MPa, sea depth 878 m.
The project has a total investment of about 2 billion euros and is operated by GalsiS.pA, a joint venture between Italy’s Edison S.pA, Enel, Sfirs, HeraTrading and Algeria Sonatrach. The stock ratio is 20.8:15.6:11.6:10.4: 41.6.
The project completed the preliminary research in 2005. In November 2007, Algeria and Italy signed an intergovernmental agreement. In 2009, the preliminary assessment was completed. It was originally planned to be completed and put into production in 2014. However, due to the significant decline in European natural gas prices in 2009, it has not yet been implemented.
6. Crossing the Trans-Saharan pipeline
The pipeline starts from the oil port of Warri, Nigeria, passes north to Niger, and ends at HassiR’Mel in Algeria. It is connected to other natural gas pipelines to Europe and indirectly transfers natural gas to Europe. The pipeline is 4,128 kilometers long, including Nigeria. The territory is 1037 kilometers, the territory of Niger is 841 kilometers, the territory of Algeria is 2310 kilometers, the pipe diameter is 1422 mm, the design pressure is 9.81 MPa, and the designed transmission volume is 30 billion cubic meters per year.
The project has a total investment of approximately US$10 billion and is constructed and operated by a joint venture between NNPC of Nigeria and Sonatrach of Algeria. The pipeline was proposed as early as the 1970s, and the project feasibility study was completed in September 2006. It was originally planned to be completed and put into production in 2015. However, due to changes in European gas prices, the project was once stranded. Due to the recent changes in the international situation, many natural gas pipelines from Russia to Europe were blocked, and the project was put on the agenda again.

Source: China Natural Gas Pipeline Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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