In cases where a joint must be taken apart and reassembled, the corrosion resistance of the fastener is particularly important so that corrosion will in no way hamper or prevent its removal. The cost of removing rusty bolts, and replacing them with new ones, is more expensive than using corrosion resistant fasteners to begin with.
Other costs resulting from fastener failure, such as downtime and lost production, make an even stronger case for consideration of high integrity fastener systems.
There was a time when the periodic repair of mechanical and electrical components was taken for granted. Today, with labor costs at record levels and going up, greater consideration at the design level is being given to the reduction—or even elimination—of maintenance.
Consequently, the designer needs to consider a fastener as a system, and regard the assembled joint as a critical and integral portion of the design, since the joint is normally an area under the highest stress and often the place where failure is most likely to occur. A designer should start with the optimum fastener and design the joint around that, rather than starting with the joint and then looking for the fastener that seems most adequate.
Decisions must be made during any failure analysis, and the results of each step dictate the next procedure. At Matergenics, our material, corrosion and mechanical engineers systematically perform required tests as deemed necessary based on the project at hand. Typical steps we often use in our root cause failure analysis investigations:
- Review of background information
- Visual and non-destructive examination
- Microscopic examination
- Physical measurements
- Corrosion examination
- Chemical analysis
- Metallurgical testing / metallography
- Fractography examination
- Mechanical testing
- Scanning electron microscopy (SEM)
- Elemental dispersive X-ray analysis (EDS)
- Fourier transformer infrared analysis (FTIR)
- X-ray diffraction
- Mechanical testing Surface analysis
- Finite elemental analysis (FEA), computational fluid dynamics (CFD) or other engineering calculations
- Determination of mode of failure and primary cause
- FEA, CFD and other detailed engineering calculations