The container is designed for a temperature of 420°C, with a design service life of 20 years; the material used is Q345R, and the thickness ranges from 36 to 60
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The design temperature of the container is 420°C, with a designed service life of 20 years. The material used is Q345R, and its thickness ranges from 36 to 60 mm. The allowable stress value on the right side of the diagram is determined by the endurance strength and creep strength at 100,000 hours of operation. Given that the designed service life is 20 years, how should the allowable stress be determined?
Q345R is not very suitable for use when the design temperature exceeds 350°C. 15CrMoR should be selected.
420 degree Q345R cannot be used; either chromium-molybdenum steel or stainless steel is required
Teacher: What I mainly want to ask is this: The allowable stress value on the right side of the thick line is determined by the endurance strength and creep strength controlled by 100,000 hours. Since the design service life here is 20 years, how should the allowable stress be selected? 20 years is more than 100,000 hours
The last edit to this post was made by wanlirn on 2019-7-29 at 17:18. Experimental data is missing; definitely not possible to use the numbers in the table directly. As I understand it, the numbers to the right of the thick black line represent the value over 100,000 hours with no usage
How was this design temperature determined? Under normal operating conditions, what is the operating temperature?
There are no real-world examples; I identified this issue by reading books. Because I saw in previous design drawings that a design lifespan of 15 years was specified; I forgot the temperature requirement. This topic is purely for academic purposes
This post was last edited by wanlirn on 2019-7-30 08:10. It might be an exam topic, but the concept of high-temperature creep limit is quite complex; in practical applications, Q345R is not used when temperatures exceed 350 degrees
There is no need to set the design life to be that long; processing thick plates is difficult.
If the operating temperature remains above 400 degrees for an extended period, and the design life is required to be 20 years, then the Q345R material cannot be used. If operations at temperatures above 400 degrees for a short period are required (such as heating the catalyst later in the process), Q345R can be used. The equipment we designed, using Q345R material and capable of withstanding temperatures over 350 degrees, has remained in good condition after 10 years of operation.
When the operating temperature exceeds 400°C, non-heat-resistant steels are not suitable. Even within 10 W-hours, its allowable stress drops sharply, resulting in a significant increase in the material thickness.