Questions regarding the quality grade requirements for ultrasonic testing of steel plates used for casings
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According to Table 3 (P46) in GB150.2-2011, 16MnDR > 20mm corresponds to a grade of not lower than II. In HG20585, 6.0.7 (P589) states that it should be no lower than grade III. So how should I choose this level? It seems like these two criteria are a bit contradictory
There is no conflict; GB150.2-2011 is a mandatory standard representing the minimum requirements； HG/T20585 is a recommended standard.
The minimum requirements for GB are already at level II, which is higher than the requirements specified in HG20585
GB150.2-2011 is a referenced standard for the Code for Pressure Vessels, whereas HG20585 is not a referenced standard for it; therefore, GB150.2-2011 should be followed.