Reasons for the stud breaking
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For the reactor I built last time, the reaction temperature was 200 degrees, while the regeneration temperature was 400 degrees for a period of 3 hours. After being in use for some time, it needed to be taken apart for maintenance; the lower cone had to be removed. However, those bolts were extremely difficult to tighten, and it took effort to break all of them before the cone could be removed. I was puzzled as to why all the bolts broke – could it be due to high-temperature carbonization? The material of those bolts was 30CrMoA. I would appreciate it if experts could analyze why they broke.
The torque required to loosen a bolt is 1.5–2.5 times the torque required to tighten it； Bolts are tightened by screwing; generally, the pre-tension stress should reach 70% of the bolt’s yield limit. Normal loosening (using a torque of 1.5–2.5 times that required for tightening) can also cause the bolts to break. In the situation described, rust on the nuts may require a higher torque to loosen the bolts. Of course, among the factors that can lead to bolt failure, the \"degradation\" of the bolt material due to high temperatures also plays a significant role.
It’s possible that the bolt and nut have seized
Two reasons: First, the strength of the screws decreases due to the operating environment； II. The screws seized, resulting in higher torque being applied, which ultimately caused them to break.
I agree with what was said on the 3rd floor: this material is fine at 400 degrees. It’s very likely that when it was screwed in, too much force was applied, causing it to get stuck; and when trying to remove it, too much force was used again, which resulted in its breaking. However, I would still recommend conducting a material analysis of the bolts; it’s quite rare for them to break, and it’s possible that there is an issue with the materials used by the equipment manufacturer
The possible reasons are estimated to be as follows: 1. The strength of the bolt material itself is insufficient. 2. Deviations occurred when machining the bolt holes. After the bolt was installed, it got stuck when trying to remove it again. 3. Slight misalignment occurred during installation; forcing the bolts to hold it in place made it difficult to remove later. 4. In high-temperature environments over extended periods, the crystal structure of the material changes, resulting in insufficient strength.
Is it a bolt or a stud? What material is used for the nut that goes with it? What is the material of the stud and what is its heat treatment status? If necessary, upgrade the performance grade of both the stud and the nut.
I agree with what was said on the fifth floor: excessive pre-tensioning can cause the stud nuts to seize, or there may be an issue with the material used by the stud manufacturer; this material should be fine for use at 400 degrees Celsius.
It’s possible that the bolts and nuts have rusted and seized!
The screws seized, resulting in increased torque being applied, which caused them to break
Temperature has some impact; I think the main issue is with the material