GB 9711-88 Spiral Submerged Arc Welded Steel Pipe Used for Petroleum and Natural Gas Transport Pipelines
GB 9711-88 is a standard for the production of large-diameter, spiral submerged arc welded steel pipe used for petroleum, natural gas, and other liquid transportation pipelines. It was developed from GB 9711-17 and GB 3625-83. The diameter range of this standard is from 914mm to 3048mm, which is the largest of all existing welding pipe production standards. GB 9711-88 is applicable to the piplines conveying petroleum, natural gas, other combustible fluids and non-combustible fluids such as water, air, steam, and gas.
This standard defines the requirements of surface quality, type and strength grade, dimensional size, weight and Straightness. It also prescribes the Production process and testing methods, as well as inspection rules. In terms of surface quality, the requirements are mainly related to the height of welds, width of welds, visible defects and reinforcement of welds. The type and strength grade are determined by its usage; for example, general mechanical components made from type Q235 steel, which has the lowest strength in steels, are mostly used for transportation and container industries; type Q345 steel is used for general structure and automated mechanical components; type Q390 steel is used for bridge construction components; and type Q420 steel is used for higher strength components.
The outside diameter and wall thickness of the pipes are determined by the nominal diameter. The outside dinmeter ranges from 1220mm to 5000mm and wall thicknesses range from 6mm to 50mm. GB 9711-88 also defines the weights and straightness of the pipes. The tolerance of weight should be ±10%. The straightness tolerance is k0=10mm/1000mm, which is the same as that of GB3625-83.
GB 9711-88 also outlines the acceptable manufacturing processes required for the production of a spiral submerged arc welded (SSAW) steel pipes. This process consists of unrolling the raw steel coil, curving into pipes, forming of the spiral joints and trimming of the ends. Each step of this proces must adhere to the strict quality requirements set forth by the standard.
The GB 9711-88 also prescribes the acceptible testing methods required before the pipes are shipped. The tests include non-destructive examination and occassional samples taken for tensile tests and chemical composition tests. Non-destructive examination includes visual inspection with calipers, liquid penetrant examination, ultrasonic testing, and magnetic powder testing. The results of these tests must meet the requirements set forth in GB 9711-88 or else the pipes cannot be accepted.
GB 9711-88 is the most comprehensive standard for the production of large-diameter, spiral submerged arc welded steel pipes used for petroleum, natural gas, and other liquid transportation pipelines. It sets forth the requirements for surface quality, type and strength grade, dimension size, weight and straightness, as well as production process and testing methods. The standards emphasize the need for rigorous inspection at every step of the production process to ensure that the final product meets the highest quality criteria.
