V-notch impact test in GB 713-2008
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6.4.1.2 states that, at the request of the purchaser and through agreement between the supplier and the purchaser, Q245R, Q345R, and 13MnNiMoR steel plates may undergo impact tests at -20°C in place of the 0°C impact tests specified in Table 2; the impact energy values must comply with the requirements set out in Table 2. The table states that the V-notch impact energy of Q345R at 0°C is not less than 34 J; then is its impact energy at -20°C also not less than 34 J?
The impact energy at -20 degrees can also reach 34 J; modern metallurgical techniques make this possible, so there’s no problem
If the designed operating temperature of the equipment is -20°C, or if there is a requirement for high toughness, then the steel plate may need to undergo impact testing at -20°C. The standards for steel used in pressure vessels are also the result of coordination among various parties; given the manufacturing capabilities of major domestic steel manufacturers, the low-temperature impact energy at -20°C is now well above 34 J.