Material selection issue!
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I am currently working on the design of a container. The specifications are as follows: design pressure of 2.0 Mpa, design temperature of 425°C, operating pressure of 1.6 Mpa, and operating temperature of 400°C. The medium involved is natural gas (with trace amounts of H2S). I have chosen 20R as the material for this application; however, I came across information in some books stating that it is better not to use 20R when the temperature exceeds 400°C. Although 20R can withstand temperatures up to 475°C, its tendency to graphitize becomes a concern when the temperature is above 425°C. I would appreciate some guidance from those with more experience
With such high temperatures and natural gas as the medium, the situation is complex; in such cases, heat-resistant steels (such as Cr-Mo steel) are the best choice. Materials at high temperatures not only have a tendency to graphitize (20R), but the hazards associated with stress corrosion in such conditions are also considerable. :P :L
Personally, I would choose Q345R material – its overall performance is better than that of Q245R, the price is roughly the same, and it’s also easy to obtain. Also, we don’t know why the temperature of the natural gas is so high; the temperature of the reformate gas we usually encounter isn’t that high.
I’m always very worried; using such equipment and relying on conventional design methods is really risky! If we could use ANSYS for stress analysis, it would give us more confidence – especially regarding the stresses at the highest temperatures. But we are just a manufacturing factory that specializes in three types of pressure vessels, and we don’t have the qualifications for analysis and design. Moreover, the equipment itself is simple, so cost isn’t a major concern; yet if we were to hire an external design firm to carry out the analysis and design for us, the cost would be beyond our means! Sigh............
4th floor – there’s no need to worry. It’s within the limits allowed by standard design criteria; there’s no need for analytical design either. The temperature is just a bit high, but standard design should be sufficient.
I agree with what was said on the 5th floor. The condition to consider when looking at the tendency toward graphitization is \"long-term use at temperatures above 425 degrees.\" I remember reading Professor Wang Fei’s view in one of his books; he believed that this period of time should be 100,000 hours, on the grounds that steel undergoes such a duration of time before reaching its creep limit and endurance strength. I still think this is a reasonable figure.
It is recommended to use Cr-Mo steel, as this provides peace of mind in the design. This parameter falls within the range of GB150; if fatigue is not a concern, conventional design methods can be used. The cost per analysis design is high.
After listening to everyone’s opinions, I will still design it according to GB150! Thank you all
From the perspective of pressure vessels alone, it is certainly necessary to consider fatigue stress and the tendency toward graphitization at high temperatures. However, a gas pipeline is merely a long-distance transmission pipeline; the high temperature specified in its design is intended solely to facilitate diffusion and meet the requirements for transportation. Moreover, long-distance pipelines experience heat losses, so while this design temperature represents the maximum temperature, there must also be a minimum temperature, which is the temperature required by the processing standards. 20R is a viable option; if concerns persist, then Q345R or Cr-Mo steel can be used.
I agree with the material choice suggested in Floor 2; considering the medium, operating temperature, and pressure, chromium-manganese steel is recommended
The medium contains (trace CH4 and H2S); CrMo steel should be used
Don’t worry; designing it according to GB150 is no problem.:lol
It’s better not to choose 20R, as this will significantly shorten the service life of the container. It is recommended to use chromium-manganese steel instead