‘Bolt failure’ – a phrase often accompanied by images of twisted metal, close-ups of corrosion or stress cracks and text throwing suspicion on sub-standard materials, design shortcuts and construction incompetence – but things are rarely as simple as they may seem…
Yes, these elements have played their part in numerous failures but even a perfect design using quality materials and assembled to tightly scrutinised industry best practice standards is no guarantee that failure can be avoided.
Why is that? Quite simply because whenever bolts are used we are measuring the wrong factors when it comes to determining that the correct ‘tightness’ has been achieved. Traditional torque tightening and hydraulic tensioning methods measure the forces applied to the bolt during tightening or stretching the bolt, rather than the tension ultimately achieved.
These methods and the mathematics involved in relating force applied to tension achieved do not include allowances for variations in friction or relaxation after the tensioning tool is released, so the ultimate tension achieved remains unknown. Erring on the side of caution to avoid reaching the bolt yield point the end result is more often than not, an under tightened joint.
From this starting point things are only going to go in one direction – joints don’t tighten themselves, so as operational stresses such as vibration or thermal cycling get to work, bolt tightness and the integrity of the joint degrades. Without effective checking and remediation, failure or leakage is only a matter of time.
Tension measurement fasteners take the guess-work out of creating leak-free / structurally sound bolted joints – How does RotaBolt work?