Installation and Maintenance of Wire Rope for Cranes

The rope on a crane is regarded as an expendable component, requiring replacement when examination shows its strength to have diminished to the point where its further use would be unwise. The working life of the rope varies in relation to the particular characteristics of the crane, its conditions and use. Where long rope life is essential, a high coefficient of utilization and high bending ratio (D/d) are adopted. Where lightness and compactness of design are essential, these values can be reduced, provided that a smaller number of operating cycles is acceptable. In all cases the safe handling of loads by a correctly operated crane depends upon regular examination of the rope, so that the rope can be removed from service before problems arise. Certain cranes function in conditions where the ropes are exposed to accidental damage, and the original rope selection would have taken this into account. In such circumstances, examination of the rope needs to be carried out with care to ensure that any critical condition of damage can be recognized and the rope can be immediately removed from service. In all conditions of use, the discard criteria relating to wire breaks, wear, corrosion and deformation can be applied immediately. These different factors are considered in this procedure which is intended to provide guidance for master, ch.officer and any other person involved in the maintenance and examination of cranes. The criteria outlined are aimed at retaining, until the rope is discarded, an adequate safety margin for the handling of loads by cranes. Failure to recognize these criteria is dangerous. The criteria has been considered on the basis of ISO 4309.

Condition before installation
Only a rope of the correct length, diameter, construction and breaking force as specified by the crane manufacturer shall be installed on the crane, unless an alternative rope has been approved by the crane designer,rope manufacturer or other competent person. Only rope terminations specified by the crane manufacturer, or alternatives similarly approved, shall be used to attach a rope to a drum, hook block or crane structure.

Rope length
The length of rope used shall be sufficient for the application for which the crane is to be used, and shall be such that in the extreme positions there are at least two wraps of rope left on the drum. When the length of rope required for use is to be cut from a longer length, servings shall be made on both sides of the cutting point, or a suitable technique shall be used to prevent the rope from untwisting when the cut is made.

Instructions from the crane manufacturer and the rope manufacturer
The instructions in the crane manual and those given by the rope manufacturer shall be followed. Before re-equipping the crane, all grooves in drums and sheaves shall be checked to ensure that they will correctly accept the replacement rope.

Maintenance
Maintenance of the wire rope shall be carried out relative to the crane, its use, the environment and the type of rope involved. Unless otherwise indicated by the manufacturer of either the crane or the rope, a rope dressing of grease or oil shall be applied during installation. Subsequently the wire rope shall be cleaned where necessary, and the rope dressing re-applied at regular intervals and before the rope shows signs of dryness or corrosion, particularly on the lengths which pass over sheaves. The rope dressing shall be compatible with the original lubricant used by the wire rope manufacturer, and shall have penetrating characteristics. If the rope dressing is not identified in the crane manual, the master shall seek adv ice from the Technical Superintendent.

Points to be covered by examination
Although the wire rope shall be examined throughout its length, particular care shall be taken at the following locations:

The termination points of both moving and stationary ropes;


 * 1) That part of the rope which passes through the block or over sheaves;
 * 2) In the case of cranes performing a repetitive operation, any part of the rope which lies over sheave(s) while the crane is in a loaded condition;
 * 3) That part of the rope which lies over a compensating sheave;
 * 4) Any part of the rope which may be subject to abrasion by external features (e.g. hatch coamings);
 * 5) Internals of the rope, for corrosion and fatigue (see Annex C);
 * 6) Any part of the rope exposed to heat.
 * 7) The results of the examination shall be recorded in the cargo gear register.

Discard criteria
The safe use of wire rope is qualified by the following criteria :

The nature and number of broken wires
The overall design of a crane is such that it does not permit indefinite rope life. In the case of 6- and 8-strand ropes, broken wires usually occur at the external surface. In the case of rotation-resistant ropes, there is a probability that the majority of broken wires will occur internally and are “non-visible” fractures. One valley break may indicate internal rope deterioration, requiring closer inspection of this section of rope. When two or more valley breaks are found in one lay length, the rope should be considered for discard. When establishing rejection criteria for rotation-resistant ropes, consideration shall be given to the rope construction, length of service and the way in which the rope is being used.

Broken wires at the termination;
Broken wires at, or adjacent to, the termination, even if few in number, are indicative of high stresses at this position and can be caused by incorrect fitting of the termination. The cause of this deterioration shall be investigated and, where possible, the termination shall be remade, shortening the rope if sufficient length remains for further use, otherwise the rope shall be discarded.

Localized grouping of wire breaks
Where broken wires are very close together, constituting a localized grouping of such breaks, the rope shall be discarded. If the grouping of such breaks occurs in a length less than 6d or is concentrated in any one strand, it may be necessary to discard the rope.

The rate of increase of wire breaks
In applications where the predominant cause of rope deterioration is fatigue, broken wires will appear after a certain period of use, and the number of breaks will progressively increase over time. In these cases, it is recommended that careful periodic examination and recording of the number of broken wires be undertaken, with a view to establishing the rate of increase in the number of breaks. This premise may be used to propose a future date for rope discard.

The fracture of strands
If a complete strand fracture occurs, the rope shall be immediately discarded.

Reduction of rope diameter, including that resulting from core deterioration
Reduction of rope diameter resulting from deterioration of the core can be caused by:

1) Internal wear and wire indentation, 2) Internal wear caused by friction between individual strands and wires in the rope, particularly when it is subject to bending, 3) Deterioration of a fibre core, 4) Fracture of a steel core, 5) Fracture of internal layers in a rotation-resistant rope.

If these factors cause the actual rope diameter to decrease by 3 % of the nominal rope diameter for rotation resistant ropes, or by 10 % for other ropes, the rope shall be discarded even if no broken wires are visible. NOTE: New ropes will normally have an actual diameter greater than the nominal diameter.

Decreased elasticity
A rope can sustain a substantial decrease in elasticity and may become unsafe for further use. Decreased elasticity is difficult to detect. If the Master or Chief Officer has any doubt, advice shall be obtained from the Technical Superintendent / or a specialist in wire ropes. As a guidance decreased elasticity However, it is usually associated with the following:

1) Reduction in rope diameter; 2) Elongation of the rope lay length; 3) Lack of clearance between individual wires and between strands, caused by the compression of the component parts against each other; 4) Appearance of fine, brown powder between or within the strands; 5) Increased stiffness.

While no wire breaks may be visible, the wire rope will be noticeably stiffer to handle and will certainly have a reduction in diameter greater than that related purely to wear of individual wires. This condition can lead to abrupt failure under dynamic loading and is sufficient justification for immediate discard.

External and internal wear
Abrasion of the crown wires of outer strands in the rope results from rubbing contact, under pressure, with the grooves in the sheaves and drums. The condition is particularly evident on moving ropes at points of sheave contact when the load is being accelerated or decelerated, and is revealed by flat surfaces on the outer wires. Wear is promoted by lack of lubrication, or incorrect lubrication, and also by the presence of dust and grit.Wear reduces the strength of ropes by reducing the cross-sectional area of the steel strands. If, due to external wear, the actual rope diameter has decreased by 7 % or more of the nominal rope diameter, the rope shall be discarded even if no wire breaks are visible.

External and internal corrosion
Corrosion of the outer wires can often be detected visually.Wire slackness due to corrosion attack/steel loss is justification for immediate rope discard. The internal corrosion is more difficult to detect than the external corrosion which frequently accompanies it, but the following indications can be recognized:

1) Variation in rope diameter - In locations where the rope bends around sheaves a reduction in diameter usually occurs. However, in stationary ropes it is not uncommon for an increase in diameter to occur due to the build-up of rust under the outer layer of strands. 2) Loss of clearance between the strands in the outer layer of the rope, frequently combined with wire breaks between or within the strands

Waviness
Waviness is a deformation in which the longitudinal axis of the wire rope takes the shape of a helix under either a loaded or unloaded condition. While not necessarily resulting in any loss of strength, such a deformation, if severe,can transmit a pulsation resulting in irregular rope drive. After prolonged working, this will give rise to wear and wire breaks. In the case of waviness the wire rope shall be discarded if, under any load condition on a straight portion of rope that does not bend around a sheave or drum, the following condition is met: d1&gt;4d/3

or, on a portion of rope that bends around a sheave or drum, the following condition is met:

d1&gt;1,1d

where d is the nominal diameter of the rope and d1 is the diameter corresponding to the envelope of the deformed rope.

Basket or lantern deformation
Basket or lantern deformation, also called “birdcage”, is a result of a difference in length between the rope core and the outer layer of strands. Different mechanisms can produce this deformation. If, for example, a rope is running over a sheave or onto the drum under a great fleet angle, it will touch the flange of the sheave or the drum groove first and then roll down into the bottom of the groove. This characteristic will unlay the outer layer of strands to a greater extent than the rope core, producing a difference in length between these rope elements. When running over a “tight sheave”, i.e. a sheave with a groove radius that is too small, the wire rope will be compressed. This reduction in diameter will at the same time result in an increase in rope length. As the outer layer of strands will be compressed and lengthened to a greater extent than the rope core, this mechanism again will produce a difference in length between these rope elements. In both cases, the sheaves and the drum will then be able to displace the loose outer strands and bring the length difference to one location in the reeving system where it will appear as a basket or lantern deformation. Ropes with a basket or lantern deformation shall be immediately discarded.

Core or strand protrusion/distortion
This feature is a special type of basket or lantern deformation in which the rope imbalance is indicated by protrusion of the core (or centre of the rope, in the case of a rotation-resistant rope) between the outer strands, or protrusion of an outer strand of the rope or strand from the core. Rope with core or strand protrusion/distortion shall be immediately discarded.

Wire protrusion
In wire protrusion, certain wires or groups of wires rise up, on the side of the rope opposite to the sheave groove,in the form of loops. Rope with wire protrusion shall be immediatly discarded.

Local increase in diameter of rope
A local increase in rope diameter can occur and might affect a relatively long length of the rope. This condition usually relates to a deformation of the core (in particular environments, a fibre core can swell up owing to the effect of moisture) and consequently creates imbalance in the outer strands, which become incorrectly oriented. If this condition causes the actual rope diameter to increase by 5 % or more, the rope shall be immediately discarded.

Flattened portions
Flattened portions of rope which pass through a sheave will quickly deteriorate, exhibiting broken wires and may damage the sheave. In such cases the rope shall be discarded immediately. Flattened portions of rope in standing rigging can be exposed to accelerated corrosion, and shall be subject to inspection at a prescribed shortened frequency if retained in service.

Kinks or tightened loops
A kink or tightened loop is a deformation created by a loop in the rope which has been tightened without allowing for rotation about its axis. Imbalance of lay length occurs, which will cause excessive wear, and in severe cases the rope will be so distorted that it will have only a small proportion of its strength remaining. Rope with a kink or tightened loop shall be immediately discarded.

Bends
Bends are angular deformations of the rope caused by external influence. Rope with a severe bend will suffer similarly to flattened portions of rope and should be treated as mentioned above

Damage due to heat or electric arcing
Ropes that have been subjected to exceptional thermal effects, externally recognized by the colours produced in the rope, shall be immediately discarded.

All examinations shall take into account the above individual factors, recognizing the particular criteria. However, deterioration frequently results from a combination of factors, giving a cumulative effect which should be recognized by the master / Ch.officer which reflects the decision to discard the rope or to allow it to remain in service. In all cases, the person examining shall investigate whether the deterioration has been caused by an abnormality in the crane; if so, then the crane problem shall be addressed first before installing a new rope. The cumulative degree of deterioration at any given position is determined by adding together the individual values that are recorded at that position in the rope. When the cumulative value at any position reaches 100 %, the rope should be discarded. Guidance for identification of recognising the particular criteria is given below which shall be used by the master and ch.officer. In case of any clarification they should contact their respective team superintendent.