Ultrasonic Testing

Ultrаsonic testing has been established as the only accurate method to measure bolt tension in the field. With over 30 years dedicated experience we are the most experienced and skillful in the world. We have solved failures on:

  • F1 Racing Engine Con-rod bolts

  • Grinding Mills

    • Liner Bolts

    • Critical Flange bolts

  • Crushers

  • Heat Exchanger Girth Joint Bolts

  • Valve flange bolts

  • Car Dumper Ring Rail bolts

  • Stacker & Reclaimer Slew Ring Bearing bolts

  • Large Bolted Tanks

Ultrasonic Testing Accuracy Properties

The standard method used to determine bolt tension is to compare the "time of flight" in the loose condition with that when tightened.

Many believe that the change in length is measured but that is incorrect. The unique and vital factor at play is the reduction in the velocity of sound due to axial bolt stress, which is 3-4 times greater than the mechanical change.

This results in extremely high accuracy readings that intrinsically have definition 3-4 times better than any mechanical method.

Our experience ranges through many industries and applications, here are a few.


Grinding Mills - Structural Bolting

Industrial Grinding Mill – Bolts Removed

As recovery grades reduce Grinding Mill sizes have had to increase. These larger machines are critical to the viability to most mine sites.

With this came new problems to solve, one of which was increased bolt failure of the structural members.

The solution is to first ensure that all bolts have precisely the required bolt tension, and second to monitor the on-going relaxation. Early detection prevents catastrophic un-planned failure.

Grinding Mills – Liner Bolting

Liner bolting has an extremely high failure rate; many sites live with failures and regularly replace bolts mid-campaign. We prevent this failure using the Ultrasonic Testing and reduce the shutdown duration.

Grinding Mills - Liner Bolting high failure rate

F1 Racing Engines

We have helped racing teams prevent engine failure caused by con rod and cylinder head breaking. In 1996 we eliminated a con-rod failure for a Formula One racing team using ultrasonic bolt stress measurement. In subsequent years we have provided solutions to many industrial, marine and commercial engine assemblers.

The applications include:

  • Cylinder Heads

  • Con-rods

  • Exhaust Manifolds

  • Engine to drive shaft couplings


Mine site crushers have an extremely arduous life cycle. Many bolt fail or loosen in service and many operators regularly have to re-tighten bolts.

We provide 3 solutions: Ultrasonic Bolt Tension Verification, optimum tightening tooling & our on line tension retaining system, Energizer.

Energizer stores energy that increases the reliability of joint assemblies, whenever parts embed causing relaxation the stored compressed energy keeps the tension in the bolts, preventing break downs.

Heat Exchanger & Pressure Vessel Solutions

Refineries, Oil Rigs, FPSO's, Power Stations and many other plants use Heat Exchangers as part of their process. These have many joint failure modes, we solve all of them but the most common are the girth joints on the heads, channels and tube sheets.

Background, the various design codes all engineers to tailor these flanges to suit the vessel dimensions. As these flanges are often individually forged they are one of the more expensive items, consequently designers seek to minimize both the thickness and diameter. This is all fine in theory but the result is normally many small bolts instead of fewer larger ones.

This page explains the challenges and solutions we provide.


Disassembled F1 Engine

Valves – Short Bolt Syndrome

OEM's often minimize valve sizes by using tapped holes; this effectively reduces the bolt effective length by 50%. This in turn reduces the required bolt elongation required to attain the correct tension. All this is fine in theory but in practice a small difference in elongation makes a significant difference to the bolt pre-load. Add to this the thermo-cyclic loading that most valves encounter and you have a recipe for failure.

Using ultrasonic bolt stress measurement and then adjusting to ensure all bolts have the correct tension ensures that these do not fail in service.


Bolt Ultrasonic Testing on a Large OEM Part

Avoid using the wrong socket. Download our free Bolt to Nut comparison chart.