About Wire Rope

Definitions,Designation and Classification
The new European Rope Staedards EN 12385-2(with the above title), EN 12385-5(Stranded Ropes for Lifts) and EN 12385-1(General Requirements) show some new requirements,we have to learn to come along with.
F.i. in the certificate,which has to accompany the rope delivery,it is required,to comply for the rope delivery,it is required to comply for the rope designation with the symbols,laid down in EN12385-2. These symbols-derived from English words are the same for all European deliveries.

Symbols for rope cores
FC=   fibre core
NFC=  natural fibre core
SFC=  synthetic fibre core
IWRC= independant wire rope core
PWRC= parallel laid full steel rope

Symbols for strand construction
S=   strand construction Seale
W=   strand construction Warrington
F=   strand construction Filler or Filler Wire
WS=  strand construction Warrington-Seale
M=   strand construction Crosslay
You can order as accustomed. Especially our Special Ropes are to be ordered as in the past by their name.

Rope class
So far each rope construction is governed by rope standards. In the new rope standards similar rope constructions in so-called rope class are aummarised,e.g. the rope constructions 6x19 Seale, 6x19 Warrington and 6x19 Filler in the rope grade 6x19. The rope standards contain tables with the technical data of the common rope grade.

Rope tensile strenth grade
For ropes acc.to EN12385-5 the rope grade adresses the nominal tensile strength grades of the outer and inner wires of the rope. Additionaly, the rope grade defines the minimum breaking strength of this rope. Rope grade 1570(without the unitN/MM2) means,that all wires of this rope are of the nominal tensile strength grade 1570N/mm2. Rope grade 1370/1770 means, that this is dual tensile rope(term of ISO4344)and the inner wires of the rope are of 1770N/mm2 nominal tensile strength grade.

Symbols for wire finish
U= bright(from uncoated)
B= galvanized acc.class B

Symbols for type of lay
sZ= right hand ordinary(or regular) lay
zS= left hand ordinary(or regular) lay
zZ= right hand lang lay
sS= left hand lang lay

Offshore Mooring Steel Wire Ropes(Extract)

1 Introduction

Steel wire rope constructions

Steel wire rope segments of mooring lines could be of various constructions as shown in Figure 1-1.

Other type of constructions may also be used if relevant experience can be documented.

The stranded rope constructions include a number of strands wound in the same rotational direction around a centre core to form the wire rope. The number of strands and wires in each strand (e.g. 6 ´ 19, 6 ´ 36, 6 ´ 61) are governed by required strength and bending fatigue considerations for the wire rope. This construction generates torque as tension increases.

The torque balanced spiral rope constructions (spiral strand, half locked and full locked coils) do not generate significant torque with tension changes. These constructions use layers of wires (or bundles of wires) wound in opposing directions to obtain the torque balanced characteristics. The half locked and full locked coil constructions consist of one or more layers of shaped wires over the basic spiral rope construction resulting in a design more resistant to the ingress of corrosion media. The shaped layer(s) of wires will also prevent any outer wire fracture from unwinding. These constructions will normally give higher load capacity related to nominal diameter due to the increased metallic area, compared to other constructions.

Figure 1-1

Steel wire rope constructions

2 Corrosion protection measures

A common design requirement is that wire rope segments in mooring lines are to be protected against corrosion attacks throughout the design life. The wire rope is therefore assumed to be fully protected such that its fatigue life approaches that in air. This is normally ensured by the following measures or combinations thereof:

— Sacrificial coating of wires.

— Application of a blocking compound on each layer of the strand during stranding. The compound should fill all crevices in the wire rope, strongly adhere to wire surfaces and have good lubricating properties.

— Surface sheathing of the wire rope by an extruded plastic jacket in order to prevent ingress of sea water and

flushing out of blocking compound.

The ends of each wire rope segment are normally to be terminated with sockets. Resin shall be used for pouring the sockets. For long term mooring the sockets should be provided with bend stiffeners (bend limiting devices). This is to protect the wire ropes from bending during installation operations when the bending radiuses are close to the minimum allowed value. To prevent water ingress in the socket a sealing system may be incorporated in the device.

Guidance for choice of wire rope construction

For long term mooring spiral ropes are normally used. These ropes maximise the available steel area and provide high strength to size ratio, high axial stiffness and limited rotation under load (i.e. torque balanced as mentioned above). Further, these constructions are considered to have high corrosion resistance since a lower proportion of steel wire area is exposed and the ingress of water to the centre of the rope is more difficult than with stranded ropes. Also, the closed and compact design of these ropes are very suitable to jacketing for added corrosion protection. Within this type of ropes half locked and full locked coil constructions have a higher wear

resistance than spiral strands because of the compact, near cylindrical surface. However, these are stiffer constructions and may, depending on the number of shaped wire layers, require more care during handling and installation. Locked coil ropes also require a larger bending radius than other constructions.

For mobile mooring stranded ropes are most commonly used. However, due to their flexibility, they may also be used in long term mooring systems as for example the upper short segment which is subject to winching damage, fairlead bending fatigue and splash zone corrosion. In these mooring systems stranded ropes may be considered as a “consumable” item which can be replaced every few years, whereas the lower segments are not intended to be replaced

Type of rope construction and extent of corrosion protection must be a case to case evaluation depending on factors like design life, level of bending stresses, environmental conditions, position of the wire rope segment in the mooring system and possibilities for replacement of the wire rope segment.

In DNV-OS-E301 Sec.4 Table I1 guidelines for choice of wire rope construction as a function of field design life and possibilities for replacement have been given. However, it should be emphasized that this table is a rough guidance and that there are no distinct limits of use for each construction.

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Properties and Choice Wire Rope

To choose wire rope,it should be according to the core requirement dependent on the opetation conditions of wire rope,at same time consider the basic features of the wire rope and then confirm the specification. 

1. Strenth

the breaking force given in the standard is the minimum one,onle applicable to the new and unused wire rope.The wire rope should not work in a condition where the required force is equal or approaching to the Min.breaking force. The actual breaking force of a new rope must be large or equal to the minimum breaking force,during the effective service life,due to the abrasion on the surface and metal fatigue, the strength of the wire rope may decrease gradually.If not beused approriately, the strength of the wire rope may vanish suddenly. For the breaking force of the ropes in same size, the rope with larger tensile strength is bigger than the one with lower tensile strength,rope with IWRC is bigger than the one with FC, linear contact lay rope is bigger than point contact lay rope, compacted wire rope is bigger than linear contact rope, double compacted is the biggest one.

2. Anti-fatigue

Anti-fatigue include the metal fatigue of the steel wire in the wire rope,to poossess a better permance
of anti-fatigue,the steel wire should possess the capability of bending repeatedly under tension. For the same size wire rope, the one which contains more small size steel wire has abetter anti-fatigue performance than that which has relative less small size. To reduce the effect of the fatigue,keep it in mind that don't wound the steel wire on the pulley or spool which has a too small diameter. The anti-fatigue performance of 6x36WS wire rope is better than 6x19 class ones, while 6x19 class is better than 6x7 class.

3.Anti-abrasion(resistant to metal loss and deformation)

Metal loss means the actual abrasion of the outer steel wire of the wire rope, this abrasion can decrease the tensile force of the steel wire; metal deformation means the shape change of the outer wire of wire rope,the change may decrease the anti-fatigue performance,then affect the move of steel wire when wire rope bends,also this may cause additional stress. For the same size wire rope,the ones which contains less outer steel wire and bigger size outer wire has a better abrasion-resistance than that which contains more outer steel wire and small size outer wire.
The compacted wire rope has relative more steel wires in one strand;it can improve the anti-fatigue performance and the anti-abrasion performance.
The anti-abrasion performance of 6x36WS class wire rope is better than 6x19 class ones,while 6x19 class is better than 6x7 class; performance of anti-abrasion of the compacted wire rope is better than that of ordinary round wire rope.

4. Anti-extrusion

Extrusion is caused by outside pressure on the wire rope, the pressure can cause deformation of the cross section, strand and the core,also can damage the wire rope when it is serious. If the wire rope is damaged by the pressure,the steel wires,strand,core can't move easily when in operation,thus additional stress is produced.Wire ropes with IWRC core have better anti-extrusion performance than the ropes with fiber core;regular lay wire ropes have better extrusion-tesistance than lang lay wire ropes. 6 strand wire ropes have better extrusion-resistance than 8 strand and 19 strand wire ropes, compacted wire rope is better than round wire rope ,double compacted wire rope has the best performance of anti-extrusion.

5. Stability

This is to describe the manenverability and the performance. There is no explicit measure method. For example,the wire rope which can be wound and can be paid off on the smooth spool,or there is not twist when being used in a assembly winding system,should be considered as a stable one. The construction of wire rope and construction is important to the stability of wire rope, regular lay wire rope is more stable than lang lay wire rope,wire rope containing 7 wire strands is more stable than these ropes which trands has more steel wires and has more complex construction.

6. Flexibility

Flexibility means the wire rope's capability of bending to arc.
Small size wire rope bends easily than big size wire rope, wire ropes with fiber core bend easily than the ones with IWRC core,bright wire rope bend easily than galvanized wire rope,point contacting wire rope bends easily than line contacting wire rope,line contacting wire rope bends easily than compacted wire rope. As a universal criterion, for same size wire rope,wire ropes compose by more small size steel wire than these composed by less big size steel wire.

7.Rotation-resistance

Wire ropes tends to rotate around the axis under the load,rotation-resistance means the capability of ratation-resistance When ratation of the clog is forbidden during the lifting operation with wire rope,then rotation-resistant wire rope should bu chosen. The rotation-resistance of 35Wx7 wire rope is better that of 18x7 class ones, 18x7 wire rope is better than compacted 4 strand wire ropes is better than 6 strand wire rope.

8. Corrosion-resistance

Corrosion-resistance of galvanized wire rope is better than that of bright wire rope, galvanized steel wire rope with imprenated plastic best corrosion-resistance.