“We sometimes underestimate the importance of little things,” wrote Charles W. Chestnutt in 1901.
Why is a torque wrench company opening a blog post about bolt failure with a quote by a turn-of-the-century author?
Because bolts are often the smallest elements of a design, but that does not make them unimportant. When bolts fail, they can do so in ways that are very catastrophic, and very public. Just ask the commuters who saw the steel rods on Oakland, California’s Bay Bridge snap in 2013.
Bolt failure can lead to fires, fatal accidents and other catastrophes. But knowing why a fastener fails can help you prevent that failure from recurring.
Common reasons for bolt failure include improper torque, improper design or manufacture, overload and metal fatigue.
Bolts that have been torqued may fail because of fatigue when:
- The initial pre-load torque value is too low, or is higher than the stress yield of the bolt
- The bolt material’s yield stress is too low
- Vibration causes the bolt to loosen
- The fastener is exposed to elevated temperatures, which leads to bolt relaxation
- The bolt is exposed to higher stress amplitudes
Reduce the chances for fatigue-related bolt failure by evaluating each bolt individually, and by considering the following steps:
Make sure the torque value in the engineering drawing is suitable for the diameter and alloy of the bolt in question
Consider tack welding the head, or using safety wire, in high-vibration conditions
Choose the appropriate strength and toughness material for the bolt
Determine that the fastener hole is clean of any dirt or corrosion, as these can lead to higher, and inaccurate, torque readings
Use rolled threads instead of cut threads to induce compressive stresses
Use additional supports to reduce operating stresses and vibrations
Inspect and retorque bolts that may have come loose
Use the appropriate torque tools for bolt tightening for every application
Wherever workers are concerned about bolt failure, Maxpro is there to help. We’ve spent more than 20 years working with clients in critical fields such as power generation, construction and the military to make sure their torque tools were properly calibrated.
We are proud of the investment we have made in state-of-the-art calibration equipment, and carry the seal of approval of A2LA, the country’s leading ISO/IEC accreditation agency.
In addition, we make sure that every torque tool we sell or rent meets ISO/IEC 17025 standards, ensuring that our customers can fasten bolts with confidence. Contact Maxpro today to learn how we can help you avoid bolt failure in your next project.