What is the reason why steel plates smaller than 6mm are exempt from impact testing?
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Why do the various standards for pressure vessels stipulate that steel plates less than 6 mm thick are exempt from impact testing? Is it inconvenient to take samples? Is it difficult to conduct experiments? Is it still because, at temperatures below 6 mm, the material properties are already sufficient to ensure its toughness within the range of temperatures at which it is used, so there’s no need for anything extra?
6mm specimens are still easy to sample from. For Dewar vessels, sheets smaller than 2.5mm don’t need to be used, so it’s certainly not difficult to conduct tests with them! Only when the size is less than 6 mm can the material properties be sufficient to ensure the toughness of the material within its operating temperature range
I have the same question: For the butt weld evaluation of Q345R, the pre-welding process evaluation requires 4mm thick plates; if 4mm thick plates are not available, can 8mm thick plates be used after being thinned down?
For steel plates under 6mm in thickness, the processing volume is high, and the material quality should be relatively uniform
During heat treatment, the 6mm steel plate has a relatively uniform cooling rate due to its thin thickness, resulting in fairly consistent properties across its upper, middle, and lower surfaces. For low-temperature materials, low-temperature impact tests are still required.
Do you mean Q245R and Q345R?
The dimensions of the standard impact specimen are: length × width × height = 55 mm × 10 mm × 10 mm. Table 2-1 on page 7 of TSG21-2016, note 2-1, specifies that when the material thickness is insufficient, it is permissible to use smaller specimens of dimensions 10 mm × 7.5 mm and 10 mm × 5 mm for impact testing; meanwhile, the acceptable value for the impact energy can also be reduced proportionally. Therefore, when the original thickness of the test piece is less than 6 mm, it cannot be processed into a 10 mm × 5 mm shape, and thus there is no reduced acceptable value available for reference; hence the standard stipulates that impact testing is not required for thicknesses below 6 mm.