Magnetic rope testing (MRT) using the “half-reel” method

Following pathologies on the carrying ropes of twin-cable ropeways in the 1970s, the decision was made to introduce Magnetic Rope Testing (MRT) into French regulations. While the most widely used method was the “full-reel” method, which is identical to the method used nowadays, a second method called the “half-reel” method was proposed to avoid lifting or moving carrying ropes on certain specific points.

The “half-reel” method designed in France proposes cutting the MRT device in two (at least the measuring part, a U-shaped magnetizing part for example, can be kept whole), in order to pass these specific points of the line, where the cable rests on a support (sheave, pulley or even roller chain) The measuring part no longer completely surrounds the cable, but usually only goes halfway round. There are no performance requirements for these “half-reel” devices, other than what is required for the whole device, i.e. “Full-reel”, see standard EN 12 927:2019.

Since the introduction of the “half-reel” method and the first analyses of its effectiveness by the Technical Service in Charge of Safety for Ropeways (STRM) in 1983, this method has been highly controversial. The Technical Service in Charge of Safety for Ropeways and Guided Transport (STRMTG) therefore decided to launch studies on the issue in order to obtain quantified information to judge their performance and try to bring an end to the controversy. This report presents the results of STRMTG’s 2013 MRT II and 2017 MRT III studies on the performance of MRT devices used in the “half-reel” method. Each of these studies recommends evaluating performance through a test derived from the test proposed in Standard EN 12 927:2019 for MRT devices used in the “full-reel” method, but adapted to the specificities of the “half-reel” method, for example by taking into account the fact that it is used for cables resting on sheaves.