Evaluation of instruments for the non-destructive testing (NDT) of wire ropes
Steel wire ropes are used for lifting, suspension, haulage and other activities across a range of industries. The integrity of wire ropes is critical to workplace safety. Traditionally rope condition has been evaluated by regular examination or mechanical testing. ln many cases industry-specific regulation is used to limit service life. With developments in rope construction and the increased use of locked coil, low rotation, die formed and plastic filled or coated ropes, traditional examination methods are becoming more difficult. Non-Destructive Testing (NDT) is an important supplement to more traditional methods. ln the UK, the "Lifting Operations and Lifting Equipment Regulations" (LOLER, 1998), permit risk based inspection rather than a traditional fixed life and NOT is used extensively for routine inspections of mining and other rope installation, Shafts and Winding in mines (1993). NDT already plays a significant role in South African rope standards (SASS 0293, 1996) and in Europe, a standard for the NDT inspection of passenger transport by ropes is in development (PrEN 12927-8, 1998). Since the mid 1970's, international research has shown that the capabilities of available NDT instruments can vary. ln 1980, work was completed by the Health and Safety Laboratory, (HSL) (previously SMRE), which examined the performance of seven European instruments on reference ropes. Comparison with earlier studies suggested considerable progress in performance (Corden, 1980). While development of magnetic heads has been progressive, the key technical changes over the last 20 years have been in data analysis and presentation. Digital recording systems and computer processing of data are becoming the norm. This change has not been without controversy and manufacturers approach the subject from many angles. ln 1999, work was completed at the University of Reading, UK, to assess the reliability of NDT equipment in terms of identifying and quantifyin91 rope degradation. Three instruments, chosen on the basis of manufacturer supplied information, were evaluated and conclusions were generally favorable, (Tytko et al., 1999). However, also in 1999, the South African Safety in Mines Research Advisory Committee (SIMRAC) commissioned the Testing and Transport Technology Laboratories in Bochum, Germany (DMT) to evaluate a range of international NOT instruments on multi-layer low rotation ropes. This work concluded that instruments and their operators derived different conclusions from the same rope (Dohm, 1999). At present, there is no international standard covering the performance of NDT instruments for use on wire ropes and no universal requirement for the qualification and training of operators or the accreditation of testing contractors. Some individual countries do have provisions in place, but requirements can vary widely, (SASS 0293, 1996 and PrEN 12927-8, 1998). NDT of wire ropes is a specialized technique with an important, but limited application compared with more established types of NDT. As a result, companies involved in its development tend to be fairly small with limited resources and customer bases. The OIPEEC Bulletin 89-2005 lack of a cohesive international approach may result from this scale of operations rather than a reluctance to standardize on procedures. ln today's environment of audited and documented quality assurance systems this may be seen as a limitation on the credibility of the technique. Attempts to address this have not benefited from a universal approach. Meanwhile, the importance of wire rope NDT is growing. An extensive world-wide study of examination techniques used for mine hoisting ropes, for the Ministry of Labour, Ontario, Canada, identified a trend towards placing more emphasis on NDT as the source of the main discard criteria for ropes (Udd, 2000). The main purpose of the HSL work was to evaluate wire rope NDT techniques and their use as a basis for discard criteria, by evaluating the performance of a number of machines selected by reputation and comparing conclusions drawn with the actual rope condition. The intention was not to rank instruments in any order.
Author(s): McCann, P. & Smith, D.