Non-destructive Testing (NDT) of steel ropes.
This HSL project, sponsored jointly by HSE, Bridon International, UK Coal Mining and Anglo American Corporation of South Africa aims to assess the ability of a range of internationally available non-destructive testing instruments to find defects in wire ropes.
Six NDT companies were selected on the basis of an earlier investigation, sponsored by Anglo American in Germany. The participants were invited to bring their instruments (seven in total) to HSL, Sheffield, for evaluation. The evaluation of each instrument was conducted jointly by the company and HSL and was carried out using six ropes of varying construction some of which contained artificial defects; others were ex-service ropes containing real defects. In addition, the instruments were taken to a local colliery so that a winding rope, known to contain defects, could be examined. The instruments were also assessed by HSL for mechanical reliability and ease of use.
Each company was to produce a report on the condition of each rope and the findings were to be evaluated by HSL. As a result of the preliminary evaluation of these test reports, it was decided to change to a more detailed post test examination regime for the rope samples.
The areas of rope that were identified as containing faults were dismantled to individual wires to assess the external and internal condition. This operation was carried out at Bridon International in Doncaster where experienced rope examination staff were available to provide help and advice. This was a slow process as the rope had a plastic layer underneath the surface layers to keep out moisture and reduce inter strand, making it difficult to pull out the individual wires. A total of 267 breaks were found and their positions recorded. The actual findings were compared with the Company's reports, and considerable variation between individual reports and observations were identified.
The findings were translated into a graphical form which will be used in the final project report. The way in which each magnetic head was constructed was discussed with the manufacturers as it had become apparent that resolution of defects was dependant on sensor type and location. This is an area that is generally not highlighted in Company literature.
The project is expected to be completed in 2002.
The final phase of this HSL project involves the revision of the “Procedure for Examining Cage Suspension Gear at Testing Centres”, originally produced by the National Coal Board and last revised in 1980. It is the only document on this subject available in the UK and many other countries use it as a basis for inspection. Many parts are now obsolescent, due to contraction of the UK mining industry, and others have been overtaken by technological advances. The aim is to produce a modern document that is less prescriptive and clearly linked to current inspection standards. Relevant findings in the earlier phases of this project will be incorporated as will recent HSE guidance in the field of non-destructive testing (NDT).
A revised draft includes preliminary comments from industry as well as those of inspection experts. The use of a “competent person” and an “authorised engineer” is proposed to undertake activities discharged previously by NCB Area Metallurgists (who no longer exist). It will be recommended that all NDT operators be trained to British Standard requirements and that they possess a nationally recognised qualification. There will be scope for the use of other inspection methods as technology advances, providing fitness for purpose can be demonstrated. The pre-cracked tests blocks, prepared in the first phase of this project, will be utilised for the purpose. Defect assessment criteria, currently specified in an Appendix, will be reviewed on the basis of fracture mechanics principles. This was examined in an earlier phase of the project.
The aim is to produce an advanced draft for further industry consultation and possible publication through the auspices of the Deep Mined Coal Industry Advisory Committee.