Another key component to a fastening strategy is managing or eliminating high risk fasteners. What are high risk fasteners? High risk fasteners are those which are subject to delayed failure, also known as hydrogen embrittlement (HE).
For a part to be considered high risk, it must have three overlapping elements:
- A hardness (core or case) in excess of Rockwell C 38
- Subjected to processing, which induces hydrogen gas, such as electroplating or acid cleaning
- Assembled in a manner which sustains high tensile or bending stress
Common high-risk fasteners are listed below:
- Property class 12.9 screws
- Alloy steel grade socket head cap screws
- Case hardened thread rolling screws
- Retaining rings
- Spring pins & clips
- Conical washers – by themselves or assembled to screws of any grade/class (SEMs screws)
Any of the above listed fasteners can be managed by selecting a finish other than electroplating which does not induce hydrogen along with using mechanical cleaning methods.