Cap Screw Failure—Hydrogen Embrittlement

Cap Screw Failure

¾-inch cap screw from an automobile suspension system.

A metallurgical failure analysis was conducted for several suspension cap screws. The cap screws were zinc plated (galvanized) and originated from an off-shore manufacturer.

Service Life

Mileage at the time of failure ranged from 30,000 to 50,000 miles.


The forensic analysis found that the recurring under-head catastrophic failures were caused by hydrogen embrittlement originating most likely from a poor cleaning and galvanizing procedure during manufacturing.