Bolt load inspection

Bolt load inspection

Test for firmly tightened bolts,
fast, without actuation and without the need of an untightened reference bolt


Industrial applications

Periodic inspection of bolts on covers of vessels, pipe sleeves, pipe sockets, bridges, etc. 


Suitable testing devices for bolt load inspection with EMAT ultrasound technology

Powerbox H 
 Powerbox H


Operation mode and features

EMAT ultrasound is used to measure the bolt load, thus avoiding errors caused by the friction conditions in the torque-based mechanical methods. EMAT can also measure the clamping force of bolts, which are not available in the untensioned state for measurements of the reference time. A special probe is used which transmits alternating longitudinal and transverse waves.
The EMAT-specific mode of operation without couplant provides extremely reliable and repeatable and temperature-independent results, even if the screw length varies slightly (product tolerances).

Bolt length of 25mm to 300mm can be inspected.

Conventional ultrasonic testing systems use only longitudinal piezoelectric transducers, which lead to coupling errors and require almost perfect surface quality. The time delay before and after the clamping must be measured for each bolt. The clamping length of the bolt has a direct effect on the measurement.

In order to measure the load on bolts, which are not accessible in the untensioned state, a method with combined longitudinal and shear waves has been developed in which the ratio of the running time of both waves can be directly used for determining the bolt load. A special dual-wave probe consisting of an EMAT coil with an integrated dry coupled piezoelectric probe alternately generates the longitudinal and shear waves.


Sensor Bolzenlast


Results of the measurement:

  • Display of values
  • A-Scan, PDF measuring report


Anzeige PZT Anzeige EMAT  Ergebnisse Bolzenlastmessung

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