The international standard ISO 4309 Cranes Wire ropes Code of practice for examination and discard is being extended to include ‘care and maintenance (including installation)’. This will be the third edition of ISO 4309 and its publication is significant for all those around the globe who are responsible for the care, installation, maintenance and examination of steel wire ropes .
The proposed changes have been under review by the committee ISO/TC 96 Cranes SC 3 Selection of Wire Ropes, a committee comprising many of the world’s leading crane and rope experts. The proposed changes have already been to inquiry and received an encouraging response.
Among many other new features, the draft guidance document introduces a system whereby any rope construction, existing or yet to be introduced to the market, can be categorised by a rope category number, or RCN, that is directly linked to the individual discard criteria covering visible broken wires. To enable the rope examiner to select the appropriate value, illustrations of rope cross-sections, corresponding RCNs and rope designations for the more familiar rope constructions are provided.
Broken wires are, of course, only one mode of deterioration. Those experienced in examination will know that ropes are more likely to deteriorate through a combination of factors, requiring an assessment of the cumulative effects of broken wires, wear, corrosion, deformations, etc. to be taken into account. To facilitate this process, new and improved reporting forms (examination record sheets) are proposed.
The standard will be further complemented by a new series of photographs illustrating various modes of rope deterioration.
Another noticeable change is the adoption of the new terms and designation system for describing ropes as detailed in ISO/FDIS 17893 Steel wire ropes definitions, designation and classification (being prepared by ISO/TC 105 Steel wire ropes), and the recently published EN 12385-2 Steel wire ropes Safety Part 2: Definitions, rope designation and classification (prepared by CEN/TC 168).
For some, the terms ‘single layer’, ‘parallel-closed’ and ‘rotation-resistant’ may be unfamiliar. They are all members of the stranded ropes family. Behind each one are a multitude of rope constructions offering properties and characteristics that enable designers to satisfy the relevant crane safety standards and meet specific performance requirements. But what are the essential differences between these three basic types of ropes and how do they impact on discard criteria? The single layer rope consists of just one layer of strands laid helically (closed) around a core, usually of steel, e.g. 6x36WS-IWRC. Apart from the odd re-positioning of a rope construction (or RCN) in the table of visible broken wires giving cause for immediate discard, the existing values remain largely unaffected.
Parallel-closed ropes consist of at least two layers of strands laid helically around a centre, usually a strand, in only one closing operation, resulting in increased metallic cross-sectional area, and hence increase strength, compared with single layer ropes. They do, however, exhibit much higher levels of rotation and torque when loaded. A typical construction is 8x19S-PWRC. The numbers of randomly distributed visible broken wires giving cause for immediate discard are the same as those for single layer ropes for the same number of outer strands and strand construction, i.e. they have the same RCN.
Rotation-resistant ropes, previously referred to as either non-rotating or multi-strand ropes, are specifically designed to generate reduced levels of rotation (when used as a single fall) or torque (when used in multiple falls) when loaded. They consist of an assembly of two or more layers of strands laid helically around a centre, but the direction of lay of the outer strands is opposite to that of the underlying layer. They differ from three and four strand ropes that can also be designed to exhibit rotation-resistant properties. With an increased risk of broken wires occurring within the rope and hidden from view, the numbers of visible broken wires giving cause for immediate discard are somewhat reduced compared to those for single layer and parallel-closed ropes.
About the author Ray Allen is a consultant specialising in steel wire ropes and former head of technical services at Bridon Rope. He is chairman of ISO/TC 105, ISO/TC 96/SC 3 and MHE/2 (BSi) and convenor of CEN/TC 168/WG 2. He is also chairman of the technical committee of EWRIS, the trade association of European wire rope manufacturers.
