Is 20g appropriate for the 470-degree intermittent operation condition?
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A certain device operates at a temperature of 470 degrees and is used in intermittent operation; the material selected is 20G. In my understanding, using 16MnR at temperatures above 370 degrees is not appropriate due to high-temperature degradation effects such as creep and graphitization. However, this device was designed quite early, in 1991; other similar devices have been upgraded to use 15CrMo. What do you all think?
In my opinion, it is not appropriate to use new standards to evaluate old equipment; it is sufficient to strengthen management of such equipment during use.
This post was last edited by liushen203 on 2010-8-25 09:06. In 1991, the industry had an insufficient understanding of materials. According to G150-89, 20R can be used up to 475 ； At that time, 20g might have been able to replace 20R (this incorrect view was corrected specifically in 1998; 20g can only replace Q235-C). From the current perspective, such a design is definitely inappropriate. It was unreasonable even at that time; GB150-89 specified that the graphitization tendency of carbon steel should be taken into account at 425 degrees. Of course, it could be argued that intermittent operation does not constitute long-term use, but from a safety perspective, 15CrMo should be preferred as much as possible. This is just my personal opinion; I welcome corrections from those more knowledgeable.
The new standards reflect technological advancements, and it is of course necessary to comply with these new requirements. Moreover, this equipment can be assessed based on its actual annual inspections and usage conditions; if there are any issues, it can be scrapped, after all, it’s almost 20 years old now! To eliminate safety hazards!
Reply to 1# realben: In such cases, it is necessary to carry out targeted testing procedures. For example, if you suspect decarburization, graphitization, or other forms of material cracking, metallographic tests should be conducted on the areas affected by high temperatures; hardness tests can also be performed to determine whether the strength of the material has decreased. . . Evaluate after the inspection. . . Again! In this case, the next inspection date for the equipment should not be set too far in the future; it’s similar to the idea that the elderly need to see a doctor regularly – old equipment also needs to be inspected more frequently. . . It’s not possible to apply current regulatory requirements mechanically to older equipment; it’s obviously not feasible to scrap and rebuild all equipment that does not meet the new standards!
For this old equipment, it should be inspected promptly to determine whether there are any issues that could affect safe production. With a service life of nearly 20 years, and given that it is equipment manufactured using previously immature standard designs, it’s better to be cautious. However, if no issues are detected during inspections, and after discussion with relevant technical personnel and experts, it can still be continued in use.