April 30th, 2008
The day before yesterday, the Wabash River IGCC’s pet coke gasifier blew up, or had a majorly pressurized blast (did it ignite? not sure…) that was felt and heard far beyond the plant boundaries. A cover over a flange opening “failed” and it failed while two workers, Danny Turner and David Shoemaker, were tightening bolts 150 feet up in the air. They were killed, and there have not been reports of other workers injured, nor has there been a statement that there were no other casualties, so we don’t know…
Anyway, a little birdie sent me a link, with the hypothesis that hydrogen embrittlement may be related to the failure. Here’s the link:
And here’s the short version, taken directly:
Hydrogen embrittlement is a major cause of fastener failure. Prevailing thought is that steels with Rockwell hardness above C30 are vulnerable. The phenomenon is well-known although the precise mechanism has eluded extensive research. A number of proposed mechanisms have been proposed, and most have at least some merit. Current thinking is that the susceptibility to hydrogen embrittlement is related directly to the trap population. Generally, hydrogen embrittlement can be described as absorption and adsorption of hydrogen promoting enhanced decohesion of the steel, primarily as an intergranular phenomenon.
Hmmmmmm, makes sense to me! A quick google brings up a boatload of references, the second one is:
Even through reported incidences of fastener failure due to hydrogen embrittlement are low, the consequences of failure can be great in equipment and piping in high pressure, flammable or toxic services. In one incident, two bolts holding the body of a ball valve together failed due to HE, separating the attached piping and releasing a propane cloud. In another instance, seven of twelve body studs in a pump containing high pressure isobutane failed due to HE. Fortunately, no one was injured in either incidence. The risk associated with bolt failures in critical services warrants prudent action to minimize this occurrence.
The following inspection and management practices associated with bolted connections are recommended:
1. Locate and document all corroded bolted connections during external visual inspections of equipment and piping, especially inspections preceding a scheduled maintenance shutdown. Corroded, high strength fasteners should be replaced during the outage and protected with a barrier coating, anti-seize compound or rust preventative.
2. Incorporate inspection of bolted connections in risk-based inspection management programs.
3. Include provisions in maintenance management procedures to protect newly installed fasteners from corrosion.
The role of counterfeit fasteners in fastener failures has received much publicity. A potentially greater hazard in the sudden failure of fasteners due to hydrogen embrittlement is less well appreciated.
So it sounds like the little birdie is on to something here. Google yourself and check it out!