High Tensile Strength Low Alloy Steel Sheet for Pressure Vessels under Low Temperature GB 3531-1996 Introduction
In an effort to improve the safety and structural integrity of pressurized vessels operating in low temperature environments, GB 3531-1996 sets forth a series of requirements as it relates to the materials used in the fabrication of such vessels. The specification is limited to low alloy, high tensile strength steel sheets used for the fabrication of pressure parts.
Requirements
The steel sheets must have a tensile strength of not less than 380 MPa and the yield point at 0.2 percent offset must be no lower than 275MPa. The materials must also have an elongation rate higher than that of the 20°C specimen by a minimum of 14%. The materials must have good working and welding properties, with only small amounts of non-metallic inclusions being allowed.
Further requirements pertaining to chemical composition and mechanical properties are also set forth in the standard. In general, the materials must have a sulfur and phosphorus content of not more than 0.05%, a minimum manganese concentration of 1.25% and a maximum concentration of 2.25%, must not contain any harmful amounts of Ni, Cu, Cr, and Mo, and must exhibit a hardness of not more than 170HB.
Test Methods
The materials must be subjected to a series of laboratory tests in order to determine their suitability for application in pressure vessels. Such tests include flattening tests, tensile tests, energy absorption tests, and impact tests.
Approval
The manufacturer must receive approval before the materials can be used for pressure vessel fabrication. The materials must be accompanied by a mill test report, which will state their chemical composition, mechanical properties, test results, and other relevant information. The materials must also meet all requirements of the specification before they can be approved.
Conclusion
Pressure vessels operate in a variety of critical environments and must be built to precise specifications in order to ensure user safety. GB 3531-1996 sets forth the standards for the materials used in the fabrication of such vessels, in particular those that must be operated in low temperature environments. The materials must have precise chemical compositions and mechanical properties and must also have good working and welding properties in order to be approved.
