Wire rope instruction
The steel wire rope is composed of multiple strands of steel wire stranded (or laid) into a rope shape. Products can be manufactured and finished with slightly different processes to improve the quality and performance of the cable. Wire ropes are widely used on boats of all types and sizes.
Wire ropes have a high strength/diameter ratio and have good resistance to wear and other forms of mechanical damage. Wire ropes require routine maintenance to prevent corrosion and are significantly heavier than synthetic ropes, which poses operational challenges for crews.
It is strongly recommended to use ropes made of independent wire rope cores (IWRC) rather than fiber core ropes. IWRC wire ropes have greater pressure resistance, higher LDBF for a given diameter, and maintain higher strength when bent.
High quality, high strength, cold drawn galvanized steel wire is recommended for mooring lines. This section does not cover wire ropes manufactured from other steel materials and processing methods. If other materials are used, the intended use, compatibility with connected equipment and maintenance should be considered.
Other steel materials and processing methods may include: high carbon steel, non-galvanized steel, stainless steel, aluminum/zinc coating and hot dip galvanizing.
For all general mooring lines, a 6x36 or 6x41 (6x36 grade) wire construction is recommended, where each strand is equidistant lay and regular (normal) right lay.
4 Factors Affecting the Performance of Steel Cables
The key factors affecting the mooring performance of wire ropes are strength, bending fatigue, tensile fatigue, extrusion and deformation, corrosion and wear, and temperature. These factors are explained in more detail below and, where feasible, provide guidance on how to address each issue.
The tensile strength of the new wire cable (ie LDBF) shall be specified in accordance with the design guidelines in Section 1. A wire with a minimum tensile strength between 1,770 and 2,160 N/mm2 is recommended. with these tensile strengths
Preformed galvanized cold drawn steel wire in strength grades is now widely available and recommended in place of non-galvanized steel wire grades.
4.2 Bending fatigue and D/d ratio
As with all ropes, the wire loses strength when bent beyond a certain radius. This is a major factor in the design of wire rope equipment on ships, as winch drums and fairleads should have adequate diameter or surface radius. The recommended minimum values listed in Section 5.2.3 are based on the use of recommended IWRC wire ropes. Fiber core ropes lose more strength than IWRC ropes at a given bending ratio. Therefore, it is not recommended to use fiber core wire rope. A minimum bending ratio (D/d) of 15 is recommended.
4.3 Fatigue and wear
Fatigue of wire ropes is mainly caused by wire bending on winch drums, pulleys or deck fairleads. Wire ropes constructed with large multi-strand wires, such as 6×19 construction, have less resistance to bending fatigue than wire ropes constructed with smaller multi-strand wires, such as 6×36 construction.
Wear on the wire may be caused by it passing over the equipment on the deck, or rubbing against itself as it is coiled on the winch drum.
4.4 Dynamic Load
A dynamic load (often referred to as a shock load) is a sudden high load that is transferred to a cable that was previously under a low or static load. This may result in peak loads higher than recommended load limits, or in extreme cases, the remaining breaking load of the cable causing the cable to fail. Repeated dynamic loading can cause a significant loss of cable strength. This is difficult to detect under normal conditions and can cause the cable to fail after a period of time, even when used below the maximum load limit. Dynamic loads in excess of the WLL should always be recorded and the cable manufacturer should be consulted for continued use.
When the winch has more than one layer of rope, high pressure on the winch or bending the wire on the deck fittings at high loads can cause crush damage. The wire rope should be reversed according to the manufacturer's guidelines
The way of tension is installed on the winch and should be coiled evenly. IWRC ropes are recommended instead of fiber core ropes because of their higher compressive strength.
Corrosion of the wire cable will increase its fatigue rate and should be avoided.
Although the use of wire lubricants and ends (such as splices and ferrules) at extreme temperatures may have limitations, in most applications wire ropes can typically be used at temperatures as low as -40°C and as high as +90°C use. Further advice should be obtained from the cable manufacturer.
5 Specifications and Sourcing
There is currently no international standard specifically for the specification of marine mooring wire ropes. Grade 6x36 steel wire is suitable for most mooring line applications. The purchaser should consult with the supplier to ensure that their required performance standards are met and that the wire rope is tested for the intended use. Appendix B provides a framework for ship operators to use when selecting wire ropes.
Wire rope products comply with many national and international standards. The following standards refer to wire ropes using the above recommended materials and constructions.
American FederalSpecification(FS)RR-W-410-F Wire Rope and strand.(6 x 37 with IWRC extraimproved plow steel).
BS EN 12385-4+A1Steel Wire Ropes. Safety. Stranded Ropes for General Lifting Applications.
BS EN 10264-2 Steel Wire and Wire Products. Steel Wire for Ropes. Cold Drawn Non-alloy SteelWire Rope for General Applications.
BS EN 13411-8 Terminations for Steel Wire Rope Safety. Swage Terminals and Swaging.
When ordering wire rope, it is best to provide as much application and background information as possible. The proposed replacement wire rope should match the performance of the existing wire rope and be compatible with the mooring design. to ensure this
For one purpose, the procurement and testing framework outlined in Appendix B shall be followed. While not all performance metrics are relevant (eg, temperature), this will help users ensure product suitability by confirming strength, stiffness, angular resistance, etc.
6 Use and maintenance
A clean, well-ventilated, dry, covered area is best, e.g. a rope store is preferred. If outdoor storage is unavoidable, the rope should be covered with waterproof material to protect it from sunlight and weather. Ropes should be stored in a location that is not easily affected by salt water, steam, chemical fumes or other corrosive substances, and should be protected from any accidental damage.
During long-term storage, the reel or winch should be turned periodically, especially in warm conditions, to prevent lubricant leakage from the wire rope and/or transfer to other areas of the mooring line. It should be ensured that the ropes do not have any direct contact with the deck and that there is air flow under the reels. Consideration should be given to installing strong simple A-frames or brackets in the rope storeroom or deck to support the reels.
Cords in storage should be checked regularly and appropriate dressings matched to the lubricant should be used if necessary. The rope supplier should be contacted for guidance on the types of dressings available and how to use them.
After completion, the wire rope should be recoiled unless otherwise specified by the manufacturer.
Wire ropes installed on winches when not in use should be covered with tarpaulins or other suitable coverings.
Wire rope installation procedures should be planned in accordance with the manufacturer's recommendations and should be carried out according to a detailed plan under the supervision of one or more professionals. To avoid accidents, ropes should be handled with care. The wire rope drum or rope reel should not fall, and care should be taken to prevent the wire rope from being damaged during handling.
Wire ropes should be inspected for damage during unloading and transport to warehouse or yard. When installing a new mooring wire rope, a turntable or similar device should always be used to avoid twisting and kinking of the wire rope due to the temporary storage drum not rotating when the rope is released.
Before the rope is installed and put into service, the relevant certificate should be obtained to ensure that the marking on the rope or its packaging is verified and corresponds to the certificate. Rope diameters and terminations should be checked to ensure they are compatible with the equipment to be installed.
More detailed installation instructions should be obtained from the rope manufacturer.
The entire length of the rope should be regularly inspected by a competent person and attention should be paid to those parts which experience has shown to be the main areas of deterioration. These include wear areas, eye loops, splices, and the portion of wire rope that sits on top of the winch when loaded during mooring operations.
Wire ropes in use may be damaged by corrosion. Corrosion affects the residual strength of the wire, but it also affects the softness and other mechanical properties of the wire, and may reduce service life.
It is recommended that the wire rope should be protected against corrosion by galvanizing the wire and using an appropriate lubricant, and re-protected as needed over the life of the wire.
The wire rope itself is not affected by UV rays, but in some cases the lubricants used may be affected by UV rays. Wire rope manufacturers should be consulted.