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The technique of Wire Rope Inspection using MFL is based around the concepts of Magnetic Flux Leakage that produces a signal which is then interpreted by a pick-up coil which produces a signal response on a strip chart. The system magnetically saturates a section of the steel rope in the longitudinal direction with the use of strong permanent (cobalt) magnet. Wherever there is a fault in that section of rope such as a broken wire, corrosion abrasion or crushing, the magnetic flux is distorted and produces a flux leakage from the rope into the surrounding air space. Sensors close to the rope sense this changing flux pattern. The magnetic flux induces electrical signals within the sensors. Signal processing circuitry modifies the test signals to make them proportional to the loss of metallic cross sectional area caused by rope defects. The signals are then recorded using a thermal strip chart recorder (or electronic data output) and the corresponding LMA/LF signals are evaluated by the inspection technician.
Triple function units can sometimes be used which incorporate a WRR signal. The WRR signal measures wire rope roughness (WRR). WRR is defined as the aggregate surface roughness of all wires in a rope. WRR is typically caused by and indicates internal and external corrosion pitting, broken wires and clusters of broken wires. The WRR signal is quantitative, and it is calibrated together with the LMA Signal. The corresponding LMA/WRR/LF triple function signals are
recorded and evaluated as above.

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The objective of this information is to outline the method of inspection to be used when carrying out Non
Destructive Examination of Ferromagnetic Wire Ropes in accordance with ASTM E1571-11.
It will at all times be the objective of any technician involved in this type of inspection, to carry out a full and thorough test and to detect, evaluate and report any relevant indications so that they can be measured against the applicable code, standard or clients acceptance criteria as stated in the NDT request or contract agreement, and ropes be either passed as good and fit for service or failed and removed from service.
All NDT Inspection’s carried out on wire ropes are a supplement to, and by no means omit the requirement for a full visual examination by a competent wire rope inspector.

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