FIELD

The present invention relates to industrial wire rope and a system for detecting wear of the wire rope and predicting remaining service life of the wire rope.

BACKGROUND

Wire ropes have been used for many decades in industrial applications. They are widely used in mooring, towing and lifting applications in the offshore industry. In the most heavy-duty applications, very expensive steel wire ropes are designed to operate at depths of 3,000-4,000 meters water depth and lifting a weight in excess of 900,000 kilograms. Typically, such wire ropes are replaced every two to five years.

Wire ropes can be generally categorised into standard and non-rotating wire ropes (commonly also called rotation resistant wire rope). Standard wire ropes can have a tendency to develop torque in use due to the twisted configuration of the strands that make up the rope, and are therefore prone to rotation. Non-rotating wire ropes are designed so that any rotational force is balanced by a counter rotation force, usually created by wrapping strands in the opposite direction as will be explained further later.

Wire ropes normally consist of three components - wires that form a strand, strands that are wrapped around a core and a core. A strand is formed by a minimum of three wires that are arranged in a geometric pattern. There are myriad geometric patterns available and in use today. The quantity, size and material from which the individual wires are made affects the overall performance of the wire rope. For example, fewer thicker wires creates greater abrasion resistance compared with a greater number of thinner wires which creates greater flexibility. Steel is often used as the preferred material for the wires. However, wires can be made from fibre (natural or man-made) or a combination of fibre and steel. In some less common applications, other materials are used for the wires.

The core has a function of supporting and retaining the strands in their positions while the wire rope is in use. The core is typically made of steel, fibre or a combination of steel and fibre.

The prior art comprises myriad designs of steel wire rope depending on the application and physical requirements and environment in which the rope will operate. Typically, standard wire rope is used for applications such as mooring and towing, whereas rotation resistant wire rope is used in subsea lifting applications and heave compensation systems.

Inspection of such wire ropes is important to determine the condition and ensure that the wire rope is safe for lifting such great loads.

A challenge with such wire ropes is that it is generally difficult to predict wear and remaining lifetime of the rope. The frequency of inspection of the rope and the method used depends on many factors. Typically, in heavy lifting operations, wire ropes are inspected at least once every twelve months. Statutory requirements in various countries demand particular inspection periods and methods. Additionally, the type of application and/or the design of the system within which the wire rope is being used has a great impact on the required frequency of inspections. Further, the operational environment and the method and frequency of operation has a major impact on the service life of the wire rope, and therefore inspection should be conducted more frequently if the wire rope is subject to harsh loading and operational environments.

The main types of deterioration of a wire rope in marine applications are fatigue, corrosion, abrasion and mechanical damage. Particular handling or incorrect use of wire ropes can also cause significant damage in a short period of time. For example, incorrect spooling of a wire rope on to a drum or badly aligned or inappropriate sheaves can cause serious damage to the rope in a short period of time.

Fatigue in wire rope is usually the result of repeated bending of the rope under tensile load. For example, a rope under tensile load may be run over sheaves and rollers, around drums and, commonly in subsea operations, through heave compensation systems. Problematically, fatigue breaks may not be visible in some forms of wire rope construction and in certain cases the breaks may only occur in internal (i.e. non-visible) wires. This may cause the wire rope to fail before there is any external indication of the wire breaks.

Subsea wire ropes are highly prone to corrosion, which is the main cause of wire rope deterioration and failure in service. Corrosion will reduce the strength of the wire rope by reducing the metallic cross-sectional area.

Abrasion occurs mostly in the outer wires of a wire rope. Wire ropes with fewer but larger outer wires give a longer working life under abrasive conditions than those with many smaller outer wires. Characterisation of condition has typically been based on visual inspection and/or magnetic rope testing (MRT). In visual inspection, the condition of the rope is inspected visually by a technician counting the number of wires that are broken and then judging whether the wire is to be discarded. The technician may also factor in the diameter of the wire rope with respect to the original or expected diameter for the service period. Different standards set some discard criteria for discarding wire ropes with a certain number of broken wires, a concentration of broken wires or breaks at certain locations. International standards ISO 4301 2017 and ISO 4309 2017 give further details.

There are many drawbacks to the visual inspection of the wires and the diameter in this way. Firstly, in terms of visual inspection, it is only possible to investigate the upper/outer wires and wire strands of the rope. Typically, these are covered in grease and are difficult to see during use. In terms of assessing the diameter, rust and wear counteract each other and can create a false impression of the diameter of the rope.

MRT is used to give an indication of loss of metallic area. Loss of metallic area effectively provides an indication of how many defects affect a rope metallic section. The assessing technician will read a percentage value, of for example, 2%, 5%, 10%, corresponding to the loss of metallic section at a defined point in the rope. In this connection, MRT provides an indication of degradation of the rope in inner and non- visible parts of the rope. The actual loss of metallic area within the rope may be due to broken, weakened and/or corroded strands within the rope. All of which may reduce the remaining service life of the rope.

Although each is useful, neither visual testing nor MRT can predict the remaining lifetime of a wire rope. Instead, visual testing and MRT will give a quantitative indication of the current status of the rope. Erring on the side of caution, since the effects of failure of industrial ropes can be catastrophic when carrying large loads, the ropes tested may be unnecessarily replaced early in their service life. Alternatively, if the inspection has not been thorough, or the assessment has been compromised by lack of clear visual assessment for example due to grease or rust, the wire ropes may be continued in service near to their fatigue limits, with potentially disastrous consequences if the wire rope is to fail in service.

In Japanese Patent Application JP 2010254394A, a steel wire is encased in resin and provided at the centre of a wire rope. During an inspection of the wire rope, a current signal is sent through the centre wire. If the centre wire is broken, this can be easily detected by the signal and this is a sign that the wire rope has reached its fatigue life and should be discarded.

The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to the prior art.

The object is achieved through features, which are specified in the description below and in the claims that follow.

SUMMARY

According to a first aspect of the invention, there is provided a strand for a wire rope for marine lifting operations, the strand comprising: a plurality of wires arranged together in a twisted configuration and comprising at least a first weakened wire and a plurality of stronger wires; such that in use when the strand is loaded in a first loading condition the first weakened wire will break and the plurality of stronger wires will not break.

The first weakened wire may be made of a different material or a different grade of material from the plurality of stronger wires.

The first weakened wire may comprise a mechanical weakness configured to cause failure of the first weakened wire at the first loading condition.

The first weakened wire may be at least partially located on the outside of the strand such that in use the failure of the first weakened wire can be visually detected.

The first weakened wire may be at least partially located on the inside of the strand such that in use the failure of the first weakened wire can be magnetically detected.

The strand may further comprise a second weakened wire such that in use when the strand is loaded in the first loading condition the second weakened wire will break.

The first weakened wire and second weakened wire may be made of a first material and the plurality of stronger wires are made of a second material, wherein the first material is a different material or different grade of material from the second material.

The first weakened wire and second weakened wire may each comprise a mechanical weakness configured to cause failure of the first weakened wire and the second weakened wire at the first loading condition.

The strand may further comprise a second weakened wire such that in use when the strand is loaded in the first loading condition the second weakened wire will not break, and when the wire rope is loaded in a second loading condition the second weakened wire will break and the plurality of stronger wires will not break.

The first weakened wire may be made of a first material, the second weakened wire is made of a second material, and the plurality of stronger wires are made of a third material, wherein the first material, second material and third material are different materials from eachother or different grades of materials from eachother.

The first weakened wire may comprise a first mechanical weakness configured to cause failure of the first weakened wire at the first loading condition and the second weakened wire comprises a second mechanical weakness configured to cause failure of the second weakened wire at a second loading condition.

The second weakened wire may be at least partially located on the outside of the strand such that in use the failure of the second weakened wire can be visually detected.

The second weakened wire may be at least partially located on the outside of the strand such that in use the failure of the second weakened wire can be magnetically detected.

The first loading condition may be a bending load.

The second loading condition may be a bending load.

The first weakened wire may be configured such that a signal can be transmitted therein, such that in use the breaking of the first weakened wire can be detected at an end of the first weakened wire.

According to a second aspect of the invention, there is provided a wire rope for marine lifting operations, the wire rope comprising: a core; and a plurality of strands wrapped around the core; wherein each strand comprises a plurality of wires arranged together in a twisted configuration; wherein at least a first strand of the plurality of strands is according to the first aspect of the invention.

At least a second strand of the plurality of strands may be according to the first aspect of the invention.

According to a third aspect of the invention, there is provided a system for detecting wear in a wire rope, the system comprising: a wire rope according to the second aspect of the invention; a magnetic sensing member for sensing a magnetic field generated in the wire rope; and a control unit for receiving data from the magnetic sensing member and for calculating a lost magnetic area of the wire rope.

The control unit may be adapted to predict a remaining service life of the wire rope based on the calculated lost magnetic area and use. According to a fourth aspect of the invention, there is provided a system for detecting wear in a wire rope, the system comprising: a wire rope according to the second aspect of the invention; and an electrical signalling device for attaching to an end of the first weakened wire and for sending and receiving an electrical signal on the first weakened wire to detect breakage of the first weakened wire.

According to a fifth aspect of the invention, there is provided a method of manufacturing a strand according to the first aspect of the invention, comprising the steps of: providing a plurality of wires comprising at least a first weakened wire and a plurality of stronger wires; and twisting the plurality of wires together; thereby forming a strand such that when subjected to a first loading condition the first weakened wire will break and the plurality of stronger wires will not break.

According to a sixth aspect of the invention, there is provided a method of manufacturing a wire rope according to the second aspect of the invention, comprising the steps of: providing a plurality of strands, at least one strand of the plurality of strands being according to the first aspect of the invention; providing a core; and wrapping the plurality of strands wrapped around the core; thereby forming a wire rope such that when subject to a first loading condition the first weakened wire will break and the plurality of stronger wires will not break.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described with reference to the following drawings, in which:

Figure 1 shows a perspective view of a prior art standard wire rope;

Figure 2 shows a cross-sectional view of the prior art wire rope of Figure 1 ;

Figure 3 shows a wire rope comprising a strand with a single wire of different material;

Figure 4 shows a wire rope comprising a strand with a single wire comprising a weakened portion;

Figure 5 shows a wire rope comprising a strand with a single wire comprising a notched portion;

Figure 6 shows a wire rope comprising a strand with two wires of different material;

Figure 7 shows a wire rope comprising a strand with two wires each comprising a weakened portion; Figure 8 shows a wire rope comprising a strand with two wires each comprising a notched portion;

Figure 9 shows a wire rope within a magnetic rope testing machine;

Figure 10 shows a graph of breaking data of an example wire rope;

Figure 11 shows a rotation resistant wire rope; and

Figure 12 shows an alternative rotation resistant wire rope.

For clarity reasons, some elements may in some of the figures be without reference numerals. A person skilled in the art will understand that the figures are just principal drawings. The relative proportions of individual elements may also be distorted.

DETAILED DESCRIPTION OF THE DRAWINGS

Figures 1 and 2 show perspective and cross-sectional views respectively of a prior art standard wire rope 100 comprising a core 110 and a plurality of strands 120, wherein each strand of the plurality of strands 120 is formed of a plurality of steel wires 130 arranged in a twisted configuration.

More specifically, the wire rope 100 comprises a single core 110 and a plurality of strands comprising a first strand 121 , a second strand 122, a third strand 123, a fourth strand 124, a fifth strand 125 and a sixth strand 126.

The first strand 121 comprises a plurality of steel wires comprising a first steel wire 131, a second steel wire 132, a third steel wire 133, a fourth steel wire 134 and so on.

The core 110 functions to support and retain the strands 130 in position while the wire rope 100 is in use.

The wire rope 100 may be visually inspected to determine wear on the wire rope 100 and to try to predict the remaining service life. As can be seen from the external view shown in Figure 1 , it is only possible to visually inspect the outer wires of the plurality of wires in the wire rope. Furthermore, when the rope is in use in a lifting application, it may only be possible to access a portion of the wire rope 100, such as an upper portion in the presently described example where the wire rope 100 is put into service in a subsea lifting operation.

Furthermore, although not shown in Figures 1 and 2, the wire rope 100 is typically covered in grease during operation to reduce friction on the wire rope 100, therefore visual assessment of the wire rope 100 is hindered. Referring now to Figure 3, there is provided a wire rope 200. It is intended that the wire rope 200 is suitable for applications such as towing and mooring of offshore structures. However, it will be understood that the presently described wire rope 200 has myriad applications in myriad industries. The wire rope 200 has some similarities to the prior art wire rope 100 shown in Figure 1, and therefore like reference numerals are used to indicate like parts. For example, the wire rope 200 comprises a core 210 and a plurality of strands 220, wherein each strand of the plurality of strands 220 is formed of a plurality of steel wires arranged in a twisted configuration. In the presently described examples steel wires are used, however it will be understood that in other examples any other suitable material may be used.

More specifically, the wire rope 200 comprises a single core 210 and a plurality of strands comprising a first strand 221, a second strand 222, a third strand 223, a fourth strand 224, a fifth strand 225 and a sixth strand 226. It will be understood that although in the presently described example, the plurality of strands 220 comprises six strands, any number of strands may be provided in other examples.

The first strand 221 comprises a plurality of steel wires comprising a first steel wire 231, a second steel wire 232, a third steel wire 233, a fourth steel wire 234 and so on.

The core 210 functions to support and retain the strands 220 in position while the wire rope 200 is in use.

The first wire 231 is configured to be weaker than the second wire 232, the third wire 233, the fourth wire 234 and the other remaining wires making up the first strand 221 , such that when the first strand 221 is loaded in a first loading condition the first wire 231 will break and the remaining wires, i.e. the second wire 232, third wire 233, fourth wire 234 and the rest of the wires making up the first strand 221 will not break.

In the presently described example, the first wire 231 is made of a different material from the second wire 232, third wire 233, fourth wire 234 and the rest of the wires making up the first strand 221. In this connection, the material of the first wire 231 is selected to be weaker than the material of the second wire 232, third wire 233, fourth wire 234 and the rest of the wires making up the first strand 221.

It will be understood that in other examples, the material of the first wire 231 may be the same material as the material of the second wire 232, third wire 233, fourth wire 234 and the rest of the wires making up the first strand 221, but the grade of the material of the first wire 231 may be different from the grade of the material of the second wire 232, third wire 233, fourth wire 234 and the rest of the wires making up the first strand 221. For example, all of the wires in the first strand 221 may be made of steel, but the first wire 231 may be made of a different grade of steel, selected such that the first wire 231 is weaker than the remaining wires.

The first loading condition is a load placed on the first strand 221. The first loading condition may a tensile load and/or a bending load. In this connection, the wire rope 200 may be under a tensile load (for example if it is performing a heavy lifting operation) and be subject to a bending load at the same time (for example if the wire rope 200 is run over sheaves and rollers or around drums in a heave compensation system). Furthermore, the loading may be of relatively low magnitude, but the wire rope 200 may have already experienced fatigue from previous loading, therefore the wire rope may be weakened. It will be understood by a person skilled in the art that the first loading condition may be any type of load on the rope, and may be reached as a result of tension and/or bending and/or twisting and/or fatigue and/or another type of loading.

As previously explained, at the first loading condition, the first wire 231 will break and the remaining wires, i.e. the second wire 232, third wire 233, fourth wire 234 and the rest of the wires making up the first strand 221 will not break. The first loading condition is predetermined to be a loading condition at which the wire rope 200 as a whole will not fail.

In the presently described example, the first wire 231 is configured to break at a first loading condition which corresponds to a remaining service life of 10% of the total service life of the wire rope 200. Said another way, when 90% of the service life of the wire rope 200 has been consumed, the first wire 231 will break but the wire rope 200 as a whole will still function, i.e. it will not break. This allows an indication of when the wire rope 200 as a whole is nearing the end of its service life, and should be taken out of service, maintained or replaced, as appropriate.

It will be understood that the exact remaining service life is difficult to predict, because although the estimated service life is typically provided by the manufacturer of industrial ropes, and the actual rope provided may have even been tested in an attempt to determine the exact service life of that particular cut of rope, it is impossible to accurately predict the remaining service life when the wire rope is exposed to varying loads and environments during service. For example, the fatigue on the rope may vary dramatically depending on the loading conditions over the lifetime of the rope. As another example, if the rope is exposed to an extreme tensile load, for example if an object which is being lifted drops and is saved by the rope, then the service life of the rope may be significantly shorted, compared to the expected service life of the rope at manufacture.

In this connection, in the presently described example, breaking of the first wire 231 provides an indication that 90% of the service life of the wire rope 200 has been consumed.

In an illustrative example, a wire rope 200 with an expected service life of two years may be provided in an offshore lifting application. The expected service life may be calculated based on normal operation of the wire rope 200 to perform lifting and running of the wire rope 200 through a heave compensation system when required. If the heave compensation system is run for a greater period of time than was expected or if the wire rope 200 is exposed to extremely high tensile load or if the wire rope 200 is not used as advised by the manufacturer, for example it is bent at too high an angle, the service life of the wire rope 200 may be dramatically reduced to ten months for example. When the wire rope 200 reaches 90% of its actual service life, at around 9 months, the first wire 231 will break, providing an indication that the total service life of the wire rope 200 has almost been consumed and the wire rope 200 should be maintained or replaced. In this case, if the wire rope 200 did not comprise a means of informing the operator of the wire rope 200 that the service life was almost entirely consumed, the wire rope 200 may have continued to be run until it failed in operation, which may have catastrophic consequences. Alternatively, knowing that the wire rope 200 was exposed to excessive bending or tensile load, the wire rope 200 may have been taken out of service after three or four months, as a safety precaution to ensure that the wire rope 200 does not fail. Taking equipment out of operation well before it is required to is expensive and time consuming.

Referring now to Figure 4, there is provided an alternative wire rope 300. The alternative wire rope 300 comprises the same major components as the wire rope 200 shown in Figure 3. That is to say, the wire rope 300 comprises a core 310 and a plurality of strands 320 each comprising a plurality of wires. In this connection, a first strand 321 comprises a plurality of steel wires comprising a first steel wire 331, a second steel wire 332, a third steel wire 333, a fourth steel wire 334 and so on. The first wire 331 is made mostly of a first material, except for a relatively small weakened portion 33T which is made of a second material. The second wire 332, a third wire 333, a fourth wire 334 and remaining wires within the first strand 321 are made of the first material. That is to say, all of the wires within the first strand 321 are made of the same first material, except for the small weakened portion 33T of the first wire 331 , which is made of a different second material. The second material is selected such that the small weakened portion 33T of the first wire 331 is weaker than the remainder of the first wire 331 and weaker than the second wire 332, third wire 333, fourth wire 334 and remaining wires within the first strand 321.

In this connection, similarly to the previous wire rope 200 shown in Figure 3, the first wire 331 of the wire rope 300 shown in Figure 4 will break before the remaining wires within the first strand 321.

It will be understood that the small weakened portion 33T may be provided by using a different grade of material in this portion 33T to provide the weakness, as previously explained mutatis mutandis with reference to the previous example.

Referring now to Figure 5, there is provided an alternative wire rope 400. The alternative wire rope 400 comprises the same major components as the wire rope 200 shown in Figure 3 and the wire rope 300 shown in Figure 4.

That is to say, the wire rope 400 comprises a core 410 and a plurality of strands

420 each comprising a plurality of wires. In this connection, a first strand 421 comprises a plurality of steel wires comprising a first steel wire 431, a second steel wire 432, a third steel wire 433, a fourth steel wire 434 and so on.

The first wire 431 comprises a mechanical weakness in the form of a notched portion 431”. The notched portion 431” has a reduced diameter compared with the remainder of the first wire 431 and the diameter of the second wire 432, third wire 433, fourth wire 434 and remaining wires in the first strand 421. The notched portion 431” is configured such that the first wire 431 will break before the remaining wires in the first strand 421.

It will be understood that the notched portion 431” is merely an example of a mechanical weakness provided such that the first wire 431 breaks before the remaining wires in the first strand 421. In other examples another type of mechanical weakness may be provided.

Referring collectively to Figures 3 to 5, it can be seen that the weakened wires 231, 331, 431 are shown in the Figures detached from the respective strands 221, 321,

421 for illustrative purposes only. It will be understood that the weakened wires 231, 331, 431 are twisted with the other wires within the strands.

Still referring collectively to Figures 3 to 5, it can be seen that the weakened wires 231 , 331 , 431 are located partially on the outside of the respective strands 221 , 321, 421 such that breakage of the weakened wires 231, 331, 431 can be easily identified by visual inspection of the wire ropes 200, 300, 400.

In some examples (not shown in the Figures) the weakened wires may be located within the respective strand on the inside of the strand. That is to say, the weakened wire may not be visible from the outside of the wire rope. In such cases, the failure of the weakened wire may be detected using magnetic rope testing techniques to identify the breakage within the strand.

For simplicity, the wire ropes described above with reference to Figures 3 to 5 have been described with a single weakened wire, i.e. the first wire 231 in Figure 3, the first wire 331 in Figure 4 and the first wire 431 in Figure 5.

However, in some examples multiple wires within the first strand 231 in the wire rope 200 may be of the same first material which is different from a second material which the remainder of the wire ropes within the first strand 231 are made of. In this connection, the first material is weaker than the second material, and so the wires made of the first material will break before the wires of the second material. This provides redundancy and also allows for a breakage to be spotted easier upon visual inspection.

Similarly, although only the first wire 331 is shown with a weakened portion 33T in the example described in Figure 4, it will be understood that in some examples multiple wires within the first strand 321 in the wire rope 300 may comprise a weakened portion 33T such that the wires comprising the weakened portion 33T will all break at the same time when the first loading condition is reached.

Similarly, although only the first wire 431 is shown with a notched portion 431” in the example described in Figure 5, it will be understood that in some examples multiple wires within the first strand 421 in the wire rope 400 may comprise a notched portion 431” such that the wires comprising the notched portion 43 T will all break at the same time when the first loading condition is reached.

Referring now to Figure 6, there is provided a wire rope 500. The wire rope 500 comprises the same major components as the wire rope 200 shown in Figure 3. That is to say, the wire rope 500 comprises a core 510 and a plurality of strands 520 each comprising a plurality of wires. In this connection, a first strand 521 comprises a plurality of steel wires comprising a first steel wire 531, a second steel wire 532 and so on.

The first wire 531 is configured to be weaker than the second wire 532 and the remaining wires in the first strand 521. The second wire 532 is configured to be stronger than the first wire 531 but weaker than the remaining wires in the first strand 521.

That is to say, the first wire 531 is the weakest in the strand 521 and the second wire 532 is stronger than the first wire 531 but is weaker than the remaining wires in the strand 521.

In this example, it can be detected when the wire rope 500 has reached a first loading condition (i.e. when the first wire 531 fails) and then when the wire rope 500 has reached a second loading condition (i.e. when the second wire 532 fails). In this connection, the wire rope 500 may be able to identify to the operator that 90% of the service life has been reached with failure of the first wire 531 and that 95% of the service life has been reached with failure of the second wire 532, for example.

This information may be useful such that the rope can be monitored closely after 90% of the service life has been reached, or the rope may be taken out of service for particular tasks which may push the rope beyond 95% of the service life. Ultimately, when the rope reaches the point where it should be taken out of service, in this case say 95%, the failure of the second wire 532 will indicate this to the operator, and the rope can then be retired, before catastrophic failure of the entire rope 500.

To achieve the desired weaknesses of the first wire 531 and second wire 532, the first and second wires may be made of a different material from each other and from the remaining wires in the strand 520. That is to say, the first wire 531 may be made of a first material, the second wire 532 may be made of the second material and the third wire 533 may be made of a third material, wherein the first, second and third materials are different. Alternatively, different grades of material may be used to achieve the desired strengths.

Referring now to Figure 7, there is provided a wire rope 600 similar to the wire rope 300 shown in Figure 4, with like reference numerals indicating like parts. The wire rope 600 comprises a core 610 and a plurality of strands 620 each comprising a plurality of wires. In this connection, a first strand 621 comprises a plurality of steel wires comprising a first steel wire 631 , a second steel wire 632 and so on. Similarly to the previously described example shown in Figure 4, the first wire 631 comprises a relatively small weakened portion 63T of a first different material or a different grade of material. Additionally, the second wire 632 comprises a relatively small weakened portion 632’ of another different material or a different grade of material.

In this way, the first wire 631 is configured to be weaker than the second wire 632 and the remaining wires in the first strand 621. The second wire 632 is configured to be stronger than the first wire 631 but weaker than the remaining wires in the first strand 621.

That is to say, the first wire 631 is the weakest in the strand 621 and the second wire 632 is stronger than the first wire 631 but is weaker than the remaining wires in the strand 621.

Referring now to Figure 8, there is provided a wire rope 700 similar to the wire rope 400 shown in Figure 5. The wire rope 700 comprises a first strand 721 comprising a plurality of steel wires comprising a first steel wire 731, a second steel wire 732 and so on.

Similarly to the previously described example shown in Figure 5, the first wire

731 comprises a first notched portion 731”. Additionally, the second wire 732 comprises second notched portion 732”.

In this way, the first wire 731 is configured to be weaker than the second wire

732 and the remaining wires in the first strand 721. The second wire 732 is configured to be stronger than the first wire 731 but weaker than the remaining wires in the first strand 621.

That is to say, the first wire 731 is the weakest in the strand 721 and the second wire 732 is stronger than the first wire 731 but is weaker than the remaining wires in the strand 721.

Referring now to Figure 10, there is provided a graph 900 showing breaking data for an example wire rope (not shown). The wire rope associated with the graph 900 comprises three weakened strands (a first weakened strand 901, a second weakened strand 902 and a third weakened strand 903). The first weakened strand 901 is 10% weaker than the remaining non-weakened strands in the rope. The second weakened strand 902 is 15% weaker than the remaining non-weakened strands in the rope. The third weakened strand 903 is 20% weaker than the remaining non-weakened strands in the rope. In this connection, as previously explained, the exemplary rope is designed such that the first strand 901 will break first, then the second strand 902 then the third strand 901, and finally, if loading of the rope is continued, the unweakened strands of the rope will fail and the rope as a whole will fail. On graph 900 an unweakened strand is marked as item 904. The x-axis shows an increasing number of bends of the wire rope and the y-axis shows an increasing number of wire breaks.

Referring now to Figure 11, there is provided a wire rope 200’. It is intended that the wire rope 200’ is suitable for applications such as subsea lifting and/or lifting using active heave compensation. However, it will be understood that the presently described wire rope 200’ has myriad applications in myriad industries. The wire rope 200' has some similarities to the wire rope 200 shown in Figure 3, and therefore like reference numerals are used to indicate like parts. For example, the wire rope 200’ comprises a core 210’ and a plurality of strands 220’, wherein each strand of the plurality of strands 220’ is formed of a plurality of steel wires arranged in a twisted configuration.

More specifically, the wire rope 200’ comprises a single core 210’ and a plurality of strands 220’ comprising a first strand 22T, a second strand 222’, a third strand 223’, a fourth strand 224’, a fifth strand 225’, a sixth strand 226’ and so on. It will be understood that the number of strands is not critical and that in other examples any number of strands may be provided. In the presently described example shown in Figure 11 , the core 210’ is not a solid core, and is instead formed of a plurality of strands. It can also be seen in Figure 11 that the plurality of strands 220’ wrapped around the core 210’ are provided in multiple layers. In this connection, each layer can be wrapped in a direction opposite to the adjacent layer, such that the rotational force created by one layer is countered by the rotational force created by the adjacent layer. It will be therefore understood that the wire rope 200’ shown in Figure 11 is a rotation resistant wire rope.

The first strand 22 T comprises a plurality of steel wires comprising a first steel wire 23T, a second steel wire 232’, a third steel wire 233’, a fourth steel wire 234’ and so on.

The core 210’ functions to support and retain the strands 220’ in position while the wire rope 200’ is in use.

The first wire 23T is configured to be weaker than the second wire 232’, the third wire 233’, the fourth wire 234’ and the other remaining wires making up the first strand 22T, such that when the first strand 22T is loaded in a first loading condition the first wire 23T will break and the remaining wires, i.e. the second wire 232’, third wire 233’, fourth wire 234’ and the rest of the wires making up the first strand 22T will not break.

In the presently described example, the first wire 23T is made of a different material from the second wire 232’, third wire 233’, fourth wire 234’ and the rest of the wires making up the first strand 22T. In this connection, the material of the first wire 23T is selected to be weaker than the material of the second wire 232’, third wire 233’, fourth wire 234’ and the rest of the wires making up the first strand 22T.

It will be understood that in other examples, the material of the first wire 23T may be the same material as the material of the second wire 232’, third wire 233’, fourth wire 234’ and the rest of the wires making up the first strand 22T, but the grade of the material of the first wire 23T may be different from the grade of the material of the second wire 232’, third wire 233’, fourth wire 234’ and the rest of the wires making up the first strand 22T. For example, all of the wires in the first strand 220’ may be made of steel, but the first wire 23T may be made of a different grade of steel, selected such that the first wire 23T is weaker than the remaining wires.

The first loading condition is a load placed on the first strand 22T. The first loading condition may a tensile load and/or a bending load. In this connection, the wire rope 200’ may be under a tensile load (for example if it is performing a heavy lifting operation) and be subject to a bending load at the same time (for example if the wire rope 200’ is run over sheaves and rollers or around drums in a heave compensation system). Furthermore, the loading may be of relatively low magnitude, but the wire rope 200’ may have already experienced fatigue from previous loading, therefore the wire rope may be weakened. It will be understood by a person skilled in the art that the first loading condition may be any type of load on the rope, and may be reached as a result of tension and/or bending and/or twisting and/or fatigue and/or another type of loading.

As previously explained, at the first loading condition, the first wire 23T will break and the remaining wires, i.e. the second wire 232’, third wire 233’, fourth wire 234’ and the rest of the wires making up the first strand 22T will not break. The first loading condition is predetermined to be a loading condition at which the wire rope 200 as a whole will not fail. The advantages provided by an early indication that the wire rope 200 is approaching failure are not repeated again for the sake of brevity.

Still referring to Figure 11, it can be seen that the wire rope 200’ comprises seventh 227’ and eighth 228’ strands which in the presently described example are not weakened like the first strand 22T. However, it is shown in Figure 11 that these strands 227’, 228’ may be in some alternative examples each comprise a weakened wire.

Referring now to Figure 12, there is provided a wire rope 200”. It is intended that the wire rope 200’” is suitable for applications such as subsea lifting and/or lifting using active heave compensation. However, it will be understood that the presently described wire rope 200” has myriad applications in myriad industries. The wire rope 200” has some similarities to the wire rope 200 shown in Figure 3, and therefore like reference numerals are used to indicate like parts. For example, the wire rope 200” comprises a core 210” and a first plurality of strands 220”, wherein each strand of the first plurality of strands 220” is formed of a plurality of steel wires arranged in a twisted configuration. As can be seen in Figure 12, there is also provided a rubber sheath 240” around the first plurality of strands 220”. The rubber sheath 240” allows a second plurality of strands 230” to be wrapped around the first plurality of strands 220”. As previously explained, the first plurality of strands 220” may provide a rotational force which is countered by the second plurality of strands 230” wrapped around the first plurality of strands 220” in the opposite direction. For the sake of brevity, the providing of weakened wires within plurality of strands 220” is not described again, however it will be understood that any number of the plurality of strands 220” may be provided with any number of weakened wires provided by any means described herein or a combination of different means described herein. In any of the described examples, the weakened wire may be provided as an electrically conducting wire such that a signal can be transmitted on the wire. In this connection, a signal may be transmitted from a point on the wire rope, such as the start of the wire rope, so that breakage of the weakened wire can be detected.

As previously mentioned, it may be hard to visually identify the weakened wire such that the integrity of the weakened wire can be determined. This may be due to the fact that the weakened wire is located within the wire rope, rather than on the outside of the wire rope, or the wire rope may be used in an environment whereby it is not easy to visually assess the wire rope, for example in subsea lifting operation. Additionally, as previously explained, the wire rope may be covered in grease or another lubricating agent, which may hinder visual assessment of the wire rope. In this connection, as shown in Figure 9 any of the example wire ropes described herein may be run through a magnetic rope testing machine 800 to determine if the weakened wires within the wire ropes have broken.