A famous example is the "Cheese grater" skyscraper in London:
Fear of failure: Why bolts on London’s Cheesegrater tower began to break
Happily, the problem, revealed by falling broken bolts was discovered before the structure failed completely. The bolts were replaces with those of a different alloy
An excerpt:
...The reason for the replacement was that they were suspected of suffering from "hydrogen embrittlement", a process that lowers the ductility of fasteners. This then raised the question among those observers who were not metallurgists, materials scientists or structural engineers as to what hydrogen embrittlement actually was.Â
The answer is that it is quite scary …Â
The nature of the problem
"Hydrogen embrittlement causes fear among engineers," says Paul Lambert, the technical director of Materials and Corrosion Engineering at Mott MacDonald, "because it attacks the fundamental reason for using steel in the first place."Â
It is also the subject of intense interest and controversy among the materials science community, owing to the competing theories of what is occurring at the atomic level.
That said, there is a consensus on the basic mechanism, which is that single atoms of hydrogen enter the steel, migrate through the crystal lattice, and are attracted to the areas of highest stress. Here they cause tiny fractures to propagate and, in a worst-case scenario, a cascading effect can take place, as the stress increases and attracts more free hydrogen, leading to a sudden catastrophic failure – such as the shearing of a bolt.
One of the unpleasant peculiarities of this process is that it particularly affects very hard steel developed for high stress uses. Lambert says: "The problem is well known and there are magic numbers – such as 320 Vickers HV – above which the risk of hydrogen embrittlement becomes greater. The first thing to ask is whether the hardness of your bolt is above that value, and if it is, you’d expect an engineer to take certain precautions..."
= new reply since forum marked as read