Looks like they had dozens of A490s snapping after tightening, likely from hydrogen embrittlement, and a big attempt to sweep it under the rug.
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stevenal said:If they are failing in use, why do the bolts appear to have been twisted apart?
dik said:Did they ever determine the cause of the hydrogen embrittlement?
galvanizeit.org said:...steel with ultimate tensile strength greater than 150 ksi may exhibit hydrogen embrittlement due to a tight grain structure trapping hydrogen molecules readily available from the pickling acid used in the galvanizing process
faceengrpe said:Some failure modes for highly stressed bolts release all of the strain energy sufficiently fast that the bolt and nut can exit the joint (opposite directions) rather fast. That is one possible contributor for the injury report. In the case of hydrogen embrittlement cracking the failure might be delayed as the cracks need some time to grow to the point of sudden failure.
electricpete said:only a small fraction overcomes torsional friction in a well lubricated thread.