Material allowable stress issue! (Different standards have different requirements.)
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Taking Q345R at 20°C as an example. According to Table 2 on page P43 of GB150-2011, the allowable stress is specified as 189 Mpa. Table 5-1 in P10 of NB/T47003 \"Steel Welded Atmospheric Pressure Vessels\" specifies that the allowable stress is 213 Mpa. Table 4.2.2 on page P9 of GB50341-2014, the \"Design Code for Vertical Cylindrical Welded Steel Oil Tanks\", specifies that the allowable stress is 230 Mpa. Why are there three different values for these three criteria?
The material standards are also different. . .
Pressure vessels generally use the lower limit value, resulting in a higher safety factor. The latter two are one at normal pressure and the other near normal pressure. So the value may lean towards the upper limit. In atmospheric-pressure vessels, there may be multiple process media, while oil tanks contain a single type of medium, so corrosion is likely to be less; therefore, the NB value is lower in those vessels compared to oil tanks.
The allowable stress is obtained by dividing parameters such as a material’s yield strength and tensile strength by a certain safety factor; different standards use different safety factors, which results in varying allowable stresses. Among various standards, the allowable stress specified in GB150 is likely to be the lowest, as it applies to pressure vessels; calculations use the most conservative values :)
The allowable stress is determined based on the relevant strength values from tests and a safety factor; these two values vary in different situations, and therefore the allowable stress also changes accordingly.
Depending on the importance of the pressure vessel, the safety factors specified by various standards vary.
The design is based on that standard, and the allowable stress is calculated in accordance with it. Mainly, the standardization periods are different, as are the safety factors.
This post was last edited by zhangjuhua on 2016-4-17 at 15:18. Indeed, but for GB150-2011 and NBT atmospheric pressure vessels, the interval of two to three years might not be the main factor; it’s more about the different levels of importance. Each case should be handled individually. I’m sorry – please ask the moderator to delete my unnecessary posts; I can’t do it myself
This post was last edited by zhangjuhua on 2016-4-17 at 15:17. For GB150-2011 and NBT standard pressure vessels, the time interval of two to three years is probably not the main factor; rather, it’s the difference in their importance that matters. Each case should be handled on its own. For the 150 standard, the value is calculated as min(σb/2.7, σs/1.5); for NBT standard pressure vessels, it might be min(σb/2.4, σs/1.5) – I’m guessing since I haven’t seen it specified, but this should be mentioned in the standard definitions
This material meets the requirements of GB713 in all cases, but when it is used in different situations, the safety factor adopted varies depending on its application and the level of risk involved. As a result, the allowable stress varies across different reference standards (tensile strength divided by the corresponding safety factor)