Remote Monitoring Of Bolt Elongation

C-Bolt is an innovative concept from Cathelain S.A., a French manufacturer of threaded components to the energy industry, that allows length checking and tightening of fastening systems and is intended for critical fastening applications that require a specific vigilance (permanent or periodic) to ensure tightening integrity.

The system principle is to integrate in the fastener (bolt, screw, stud …) a 0.25 mm diameter optical fiber placed in an axial hole of 0.5 mm at the center of the fastener and fixed to the fastener by a polymerized bonding which resists to temperatures -268°C to 320°C. The patented optical fiber technology process is based on “polarimetric interferometry of white light”. The process allows measuring tiny variations of the fastener length by emission of a spectrum of a light wave which is projected on a set of mirrors. The corresponding signal is analyzed to determine the fastener lengthen with a precision of 0.5 µm/m.

The fiber optical connection can be completed before or after the fastener tightening using the plug connector which links the sensor to the recording device. Cable length up to 3.5 km is possible and one recording device can be connected to 1300 sensors. Information is communicated to a customizable interface which checks the variation curve of the lengthening in real-time and which can alert based on alarm set-up parameters.

C-Bolt can be installed in various types of industrial environments. It does not produce any signal and not sensitive to gamma or beta rays, or magnetic fields or frequencies. Only the recording device, which can be remotely installed, is requiring an electric input.

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