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Wire Rope Testing – An Introduction to Magnetic Flux Leakage Testing

Updated: Jul 31, 2020

Introduction

Wire rope testing with magnetic flux leakage (MFL) is a well-developed non-destructive testing (NDT) technique for wire rope inspection. The measurement instrumentation is designed to detect local faults (LF) and loss of metallic area (LMA). Local faults are generally wire breaks while loss of metallic area is generally categorized as a gradual or extended loss in cross-sectional area due to corrosion, wear, or other wire rope deterioration mechanisms. This article introduces the reader to the MFL wire rope testing hardware and data.








Magnetic Flux Leakage Reference Documentation

There are a various important standards published by the American Society for Testing of Materials (ASTM), European Standards (DIN) and International Standard Organization (ISO) on the topic of wire rope inspection and rejection criteria. These include but are not limited to:


- ASTM E 1571: Standard Practice for Electromagnetic Examination of Ferromagnetic Steel Wire Rope


- DIN EN 12927-6: Safety requirements for cable way inspections designed to carry persons Part 6: Discard Criteria


- ISO 4309:2017 Cranes - Wire Ropes - Care And Maintenance, Inspection And Discard

These standards are applicable to a wide variety of machines ranging from mobile cranes, tower cranes, cantilever cranes, and cable ways for carrying people. These MFL testing standards lend themselves to many industries including: mining, transportation, maritime, amusement parks, and leisure industries.


In additional to ASTM, DIN and ISO standards there are a variety of regional codes that outline wire rope inspection requirements. For example, the New Jersey Administrative Code (NJAC) Chapter 14A Carnival – Amusement Rides outlines wire rope inspection frequency and discard criteria. In this regional code the wire rope discard criteria is fairly straight forward and is summarized below:


- In running ropes, six randomly distributed broken wires in one rope lay or three broken wires in one strand in one rope lay;


- In pendants or standing ropes, evidence of more than one broken wire in one rope lay;


- Any condition which causes the loss of more than one-third of the original diameter of the outside individual wires;


- Severe corrosion;