Materials for Tees Used for China-Russia East Pipelines
Posted: 12/25/2022 01:05:55 Hits: 6
The selection of the material
The material of pipe fittings should be the same or similar to that of the connected pipe. The design temperature of the pipe fittings of the China-Russia East Station is -45°C. At present, there are no standards for high-impact carbon steel and low-alloy steel low-temperature pipe fittings for oil and gas pipeline station projects in China. The available low-temperature pipe fitting materials in the existing standards and product systems are Q345E with a minimum allowable working temperature of -40°C in GB 6479-2013 "Seamless Steel Tubes for Fertilizer Equipment", 09MnD and O9MnNiD with minimum allowable working temperatures of -50°C and -70°C in GB 150-2011, the minimum allowable, but the maximum allowable wall thickness does not exceed 8 mm. GB/T 18984-2016 "Seamless Steel Tubes for Pipelines" also lists low-temperature materials with 5 grades. The lowest allowable operating temperature is below -45°C. However, the yield strength of the above low-temperature materials is relatively low, with a maximum of no more than 345MPa, which cannot meet the construction needs of high-pressure, large-diameter gas pipelines.
The low-temperature pipe fittings in the high-pressure and large-diameter gas pipelines that have been built in China mainly use the pipeline in steel specified in GBT 9711-2017 "Steel Pipes for Pipeline Transmission Systems in the Natural Gas Industry". The design department should make corresponding regulations on the low-temperature toughness index based on the working conditions. It is difficult to guarantee the low-temperature toughness of domestic pipe fittings below -30°C due to the limitations of the pipeline steel alloy systems. The minimum design wall thickness of equal tee used with pressure of 12MPa and size 1200 mm X 1200 mm in the west section of the Third West-East Gas Pipeline Project is 49 mm, and the material is X80, which can meet a temperature of -30°C.
For the selection of pipe fittings in foreign gas pipeline stations, when the temperature is low, low-pressure, small-diameter pipe fittings generally adopt the corresponding grades of materials in ASTM A333/A333M-2016 "Specifications for Seamless and Welded Steel Pipes for Low Temperature". The minimum allowable working temperature of the material is lower than -45°C. For high-pressure and large-diameter pipe fittings, the corresponding grade of steel pipe material in API SPEC 5L-2018" Specifications for Pipeline Steel" is generally used, and specific requirements are put forward for low-temperature impact toughness. The only natural gas pipeline with a diameter of 1422 mm in low-temperature regions that has been put into operation abroad is the Bafarenko-Uyi natural gas pipeline in Russia. The material is K65 (X70), and the design temperature reaches -45°C.
According to the requirements of the standard and referring to the relevant engineering experience at home and abroad, X80 is selected as the material for the tee with a diameter of 1422 mm × 1219 mm on the China-Russia East Pipeline. Because the manufacture of domestic X80 cannot meet the low-temperature toughness index requirements of -45°C. China National Petroleum Corporation carried out technical research, combined with the single furnace trial production and evaluation results of tees, and completed the composition design for X80 low-temperature special plate through multiple rounds of chemical composition adjustments. The low-temperature toughness of the developed products can meet the design requirements of the China-Russia East Pipeline at -45°C.
The material of pipe fittings should be the same or similar to that of the connected pipe. The design temperature of the pipe fittings of the China-Russia East Station is -45°C. At present, there are no standards for high-impact carbon steel and low-alloy steel low-temperature pipe fittings for oil and gas pipeline station projects in China. The available low-temperature pipe fitting materials in the existing standards and product systems are Q345E with a minimum allowable working temperature of -40°C in GB 6479-2013 "Seamless Steel Tubes for Fertilizer Equipment", 09MnD and O9MnNiD with minimum allowable working temperatures of -50°C and -70°C in GB 150-2011, the minimum allowable, but the maximum allowable wall thickness does not exceed 8 mm. GB/T 18984-2016 "Seamless Steel Tubes for Pipelines" also lists low-temperature materials with 5 grades. The lowest allowable operating temperature is below -45°C. However, the yield strength of the above low-temperature materials is relatively low, with a maximum of no more than 345MPa, which cannot meet the construction needs of high-pressure, large-diameter gas pipelines.
The low-temperature pipe fittings in the high-pressure and large-diameter gas pipelines that have been built in China mainly use the pipeline in steel specified in GBT 9711-2017 "Steel Pipes for Pipeline Transmission Systems in the Natural Gas Industry". The design department should make corresponding regulations on the low-temperature toughness index based on the working conditions. It is difficult to guarantee the low-temperature toughness of domestic pipe fittings below -30°C due to the limitations of the pipeline steel alloy systems. The minimum design wall thickness of equal tee used with pressure of 12MPa and size 1200 mm X 1200 mm in the west section of the Third West-East Gas Pipeline Project is 49 mm, and the material is X80, which can meet a temperature of -30°C.
For the selection of pipe fittings in foreign gas pipeline stations, when the temperature is low, low-pressure, small-diameter pipe fittings generally adopt the corresponding grades of materials in ASTM A333/A333M-2016 "Specifications for Seamless and Welded Steel Pipes for Low Temperature". The minimum allowable working temperature of the material is lower than -45°C. For high-pressure and large-diameter pipe fittings, the corresponding grade of steel pipe material in API SPEC 5L-2018" Specifications for Pipeline Steel" is generally used, and specific requirements are put forward for low-temperature impact toughness. The only natural gas pipeline with a diameter of 1422 mm in low-temperature regions that has been put into operation abroad is the Bafarenko-Uyi natural gas pipeline in Russia. The material is K65 (X70), and the design temperature reaches -45°C.
According to the requirements of the standard and referring to the relevant engineering experience at home and abroad, X80 is selected as the material for the tee with a diameter of 1422 mm × 1219 mm on the China-Russia East Pipeline. Because the manufacture of domestic X80 cannot meet the low-temperature toughness index requirements of -45°C. China National Petroleum Corporation carried out technical research, combined with the single furnace trial production and evaluation results of tees, and completed the composition design for X80 low-temperature special plate through multiple rounds of chemical composition adjustments. The low-temperature toughness of the developed products can meet the design requirements of the China-Russia East Pipeline at -45°C.
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