Unexpected fastener failure can catch anyone off-guard, especially after a product has been assembled and/or shipped to customers. One of the most common types of damage involves hydrogen embrittlement, a phenomenon that weakens and eventually destroys fasteners from within, leading to sudden breakages that not only compromise the products and structures they secure but also prove costly to rectify.
There is nothing new about hydrogen embrittlement. Experts uncovered the phenomenon as far back as 1875, but such failures remain poorly understood among many. The nature of hydrogen embrittlement also makes it nearly impossible to detect via in-process control or through outbound quality checks, since embrittlement develops long after fastener manufacture.
It is no wonder that hydrogen embrittlement, also known as hydrogen attack, is considered the silent killer of fasteners and other metal products.
Types of Hydrogen Embrittlement
Hydrogen embrittlement comes in two forms:
• Environmental hydrogen embrittlement – Caused by hydrogen externally introduced to the fastener, usually through corrosion, while the fastener is under a high-tensile load. Constant exposure to saltwater or acidic rainwater can factor into embrittlement and eventual fastener failure.
• Internal hydrogen embrittlement – Caused by the introduction of residual hydrogen during the manufacturing process. Certain cleaning and plating processes can introduce free hydrogen atoms into the fastener, setting the stage for embrittlement after manufacture.
Hydrogen embrittlement affects a broad range of metals and alloys, but the phenomenon is typically associated with carbon and alloy steels. Failures due to hydrogen embrittlement typically occur only when the fastener is placed under tensile stress.
Prevention and Relief Choosing an appropriate surface treatment that does not introduce hydrogen during the plating process can help prevent internal hydrogen embrittlement. The Bossard Expert Team’s own Peter Witze authored a white paper that goes further in-depth about hydrogen embrittlement, including critical values of hydrogen concentration and procedures to inspect fasteners for hydrogen embrittlement. Download the white paper here.
