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Bridge Failure Sparks Concern Over Hydrogen Embrittlement
Engineers know hydrogen embrittlement is a bad thing. However, ask many to explain what it is and how to avoid it, and you may be met by silence.
The phenomenon occurs when hydrogen atoms penetrate the crystalline molecular structure of metals and weaken the bonds.
The effect is that elongation and ductility is severely reduced. Parts that fail because of hydrogen embrittlement have almost no plastic deformation, with the fractured cross-sections looking more like a ceramic.
The problem is well known by industrial fastener manufacturer, EJOT. Its sales manager for industrial products Steve Wynn, explains the problem: "There are two causes of hydrogen embrittlement; where hydrogen from the environment assists with the failure i.e. corrosion, and where hydrogen from the manufacturing process assists with the failure."
Hydrogen embrittlement is well known to fastener suppliers that know it can be induced during electroplating, heat treatment and also cleaning (pickling) processes during manufacture.
However, overlooked and misunderstood are the effects of the environment, especially on highly stressed large bolted joints. This is the realm of designers and specifiers. Uckfield based TR Fasteners has experienced various cases in the past where large bolted joints have unexpectedly failed because of poor specification, and not manufacturing errors.
"We are a manufacturer and supplier of components and we don't always get told where our fasteners end up," says Geoff Budd, managing director at TR Fastenings. "And that is why this is such an important topic. People think when they have this sort of failure it is caused by problems during manufacture, but actually it's often the specification that has brought on the phenomenon. That is why we want to educate customers, and get designers to fully understand it."