Breakage of foundation bolts in liquid ammonia storage tank fabrication
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Today, it was discovered that two of the foot bolts at the sliding end of the saddle of the liquid ammonia storage tank, which has a diameter of 2.2m and a length of 10m, were broken. What warning can this serve as?
Is it possible that, if the sliding bolt is not loose, the saddle may also experience alternating tension and compression due to temperature changes associated with seasonal shifts, leading to fatigue and eventual fracture? Because the device is long, reaching 10m. The amount of elongation during thermal expansion cannot be underestimated. The other several storage tanks are shorter, at 7m. No broken bolts were found. Another question is: what is the worst accident that could happen if new bolts are not replaced? Thank you!
This post was last edited by nj1952 on 2017-6-21 at 20:31. From the photos, it can be seen that the fracture surface of the anchor bolts is flat and brittle, with no plastic deformation, indicating that the properties of the material have changed. The specific reason can only be determined through failure analysis. The author has encountered a situation where, during the installation of a large motor, the foot bolts broke as a result of being struck with a 0.5 kg hammer. Subsequent failure analysis revealed that during the hot processing of manufacturing the buried hooks for the forged foot bolts, improper temperature control led to overheating of the material, enlarged grain sizes, reduced strength, and premature failure of the foot bolts. It should also be noted that the saddle bottom plate must not be welded to the foundation’s embedded floor; otherwise, the sliding bearing will not function properly. Under these operating conditions, the possibility of metal fatigue is virtually none (the frequency of cyclic loading cannot exceed 10 to the 7th power). Additionally, basic requirements for installing horizontal containers: the sliding side foot bolts and the circular holes in the supports must not prevent the equipment from expanding and sliding ； The nuts securing the side foot bolts are tightened evenly and reliably ； Smooth the sliding surface and apply grease ； After the installation of the equipment and pipelines is completed, loosen the nut on the sliding side to leave a gap of 0.5–1 mm.
Great, thumbs up; I agree with your view.
This post was last edited by A calm mindset HAPPY on 2017-6-21 22:08. Do you think the issue lies in the quality of bolt manufacturing, or do I still doubt that foundation bolts could be so fragile? However, the bolts on the other machines were all tight, and the installation requirements were not strictly followed. What worries me now is that, assuming the bolt is in good condition before installation, what amount of tension would be required to break such a bolt, and whether the circumferential welds on the cylinder might get damaged. Moreover, the medium is liquid ammonia, which has a tendency to cause stress corrosion cracking in carbon steel. As a supplementary note, I only discovered it on site today; the break likely occurred a long time ago, and the broken bolts had already been removed by someone, so they can no longer be found. I have indeed seen bolts on oblong holes break due to fatigue before; I’ll find some photos and share them with everyone. The fracture surface also showed no plastic deformation.
Why are the anchor bolts of the sliding layer breaking? Since no force is applied here, it’s not possible that the sliding layer is connected to the tank. It is recommended to check whether it can slide freely
Reminder: What the poster should do now is: (1) After checking that the sliding side foot bolts are broken, if the broken ends are above the equipment foundation and are positioned close to the circular hole in the support, thereby preventing the equipment from expanding and sliding (as can be seen from the photos, the ammonia storage tank is not installed properly, with the sliding side foot bolts being close to one end of the oval hole in the support), a chisel should be used to remove the exposed parts； (2) The nuts of the fixed-side foot bolts are tightened evenly and securely ； (3) Check the fillet welds connecting the saddle support web to the ammonia storage tank shell for any signs of cracking (visually inspect the paint coating for signs of cracking); if any such signs are found, magnetic particle testing can be performed on them ； (4) Check whether the piping of the ammonia storage tank is deformed under thrust.
The sliding ends of the other few devices are all secured; they aren’t loose. For these as well, it can be assumed that they aren’t loose.
The photo might have been taken from a poor angle; the bolt is in the middle of the long hole. The points you mentioned are very important; let’s plan for them next. Thank you!
It can be determined from the absence of scratches on the edge of the oval hole that the nut is not tightened, but is in a loose state
What is the possibility of the bolt breaking when it is in a loose state?