Classification of strength grade of seamless steel pipe
The strength grade of seamless steel pipe is generally divided according to the size of the ultimate tensile force. Common strength grades are as follows:
1. Ordinary strength seamless steel pipe
Its strength grade is A, and the ultimate tensile force is 4.45MPa. It is mainly used in general mechanical processing and regular low-stress working environment.
2. High-strength seamless steel pipe
Its strength grades are B, C, and D, and the ultimate tensile forces are 6.24MPa, 7.85MPa, and 9.45MPa respectively. It is suitable for working environments that need to withstand high strength, such as offshore platforms, ship structures, high-pressure pipelines, etc.
3. Ultra-high strength seamless steel pipe
Its strength grade is E, and the ultimate tensile force is 11.77MPa. It is used in some occasions that need to withstand high strength requirements in special environments, such as aerospace, automobile body structures, etc.
(1) For pipe fittings whose grade is expressed by nominal pressure or whose pressure-temperature rating is specified, the pressure-temperature rating specified in the standard shall be used as the basis for their use, such as GB/T17185;
(2) For pipe fittings whose standard only specifies the nominal thickness of the straight pipe connected to it, their applicable pressure-temperature rating shall be determined according to the benchmark pipe grade specified in the standard, such as GB14383~GB14626.
(3) For pipe fittings whose standard only specifies the external dimensions, such as GB12459 and GB13401, their pressure-bearing strength shall be determined through verification tests.
(4) For others, the basis for their use shall be determined by pressure design or analytical analysis in accordance with relevant regulations. In addition, the strength grade of pipe fittings shall not be lower than the pressure under the severe working conditions that the entire pipeline system may encounter during operation.
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