Hydrogen embrittlement (HE) is a delayed, catastrophic failure of a bolted joint. The biggest indicator of this type of failure is that it occurs after installation, within 24 – 48 hours, but never during assembly. Common candidates for this type of failure are high strength, electroplated, threaded parts. Other non-threaded, high strength electroplated parts such as retaining rings, lock washers and spring pins may also be at risk. Threaded parts which have failed from HE will break at the fillet radius under the head, or at the first stressed thread root and not show any signs of stretching or necking down.
Three things must be present for HE to be a concern:
- High strength steel, greater than Rockwell C 36
- Introducing hydrogen through a process such as acid cleaning, electroplating or corrosion
- A high sustained tensile or bending load must be present
Eliminating any one of these three conditions will eradicate the risk of HE.
If you have a delayed failure, look for the three conditions above and contact your fastener experts at Bossard at ProvenProductivity@bossard.com for more analysis.What Is Hydrogen Embrittlement? by Bossard