Holdfast Training Services Trial Blog

Ever had issues on site with proving bolts are tightened correctly? Normally this results in using the part turn method or a torque bar/gun but often there are challenges determining the correct ‘torque’ compared to the required bolt tension. What if there was another way?

This American company (Smart Bolts) are offering smart bolts with an indicator that changes colour as the bolt is tightened. The colour change is based on bolt extension which is linked to tensile force (F = ke in the elastic range). Below is a video demonstration/sales pitch of how it works.

https://youtu.be/3Uclf_Ciet8

Pros:

• Visual indication when ‘correct’ tension is reached.
• Simplicity on site.
• Torque equipment or testing of bolts isn’t required.
• Bolts can be re-used provided elastic limit is not exceeded.
• Ease of checking during operational use/maintenance.

Cons:

• Bolts cost more than standard bolts.
• Codes/APoC may not recognise the installation method.
• Increased to me to verify each bolt’s colour change.
• Colour changes are at set increments based on bolt design limit and may not correlate to site purpose/requirements.
• Operational service life ‘over 20 years’ may not be long enough for structural steel applications.

I’m interested to see how this technology develops in structural engineering applications. There may already be some military engineering applications where the bolts would be useful. What do you think?