Mar 302013

If you want to trash  a steel structure, one way to do it is to introduce hydrogen. Hydrogen can diffuse into the steel from outside, or it can be introduced during manufacturing; it then seems to work in much the same way that water and water ice introduced into micro-cracks in rocks can, over time, expand and contract to cause the cracks to be forced apart. Hydrogen embrittlement is a well-known phenomenon, and is of course to be avoided for any important load bearing steel structure. It’s fairly rare… it’s actively avoided in manufacturing, and where do most structures encounter molecular or atomic hydrogen out in the wild? But then this happened:

Hydrogen found in damaged Bay Bridge steel rods

It seems that 32 large steel rods on the new eastern span of the Bay Bridge connecting San Francisco to Oakland snapped, with hydrogen detected in at least some of the broken rods.

There was apparently a bit of a controversy over the steel used in constructing the bridge… the bulk of it came from China. But the bolts in question came not from China, but from Ohio. It appears that the hydrogen was probably introduced into the rods during the galvanizing process; water dissolved in the molten zinc the rods were dipped in broke down into hydrogen and oxygen. The high temperature only made the hydrogen diffusion into the steel that much more effective.

The rods in question are part of the system to protect the bridge against earthquakes. Ooops.

 Posted by at 8:18 am