Knowing how to check bolt torque is a key ingredient in making sure fasteners don’t fail. There are several ways to determine bolt torque, including torque auditing.

As Bill Eccles of Bolt Science writes, there are three ways this can be achieved:

1. The on-torque method – This is the most commonly used form of torque auditing, measuring the torque required to turn the bolt/nut by a small angle (usually two to 10 degrees) in the tightening direction.

2. The off-torque method – This method involves measuring the torque needed to rotate the bolt/nut in the untightening direction (this is usually less than the tightening torque).

3. The marked fastener method – This requires you to mark the position of the bolt and nut relative to the joint, loosening it by an angle of approximately 30 degrees, then measuring the torque needed to get the bolt back to the marked position.

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“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.

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Wind turbines are held together with bolted joints that are under constant attack from vibration, fatigue, corrosion and bolt relaxation.

Windpower Engineering magazine lists a few things professionals in the wind industry – especially those in the market for new wind turbine torque tools – should know about tightening and tensioning.

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We’ve used this blog to talk about quality control before, but today we’re going to approach this topic from a new angle: quality control as it relates to bolt tightening.

As the website Bolt Science puts it:

“It is no longer sufficient just to run a nut down a bolt until it stops and hope that it is tight enough. A single bolt, inaccurately or incorrectly tightened, can lead to the failure of the complete product.”

If a bolt torque is too tight, you risk a stripping or bolt shank failure. If the torque is too low, the bolt tension won’t meet functional requirements. Either outcome can cause significant problems.

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