Wire Rope Integrity for Winch-Assisted Forestry Equipment

Wire Rope Integrity for Winch-AssistedForestry EquipmentJune 2017 – Technical Report 36Brian Boswell, Senior Scientist – Fibre SupplySam Field, Researcher – Roads and Infrastructure

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30101442: Cable Integrity

Technical Report 36

REVIEWERSWoodam Chung, Oregon State University

Jean-Francois Gingras, Manager, Fibre Supply

Tyson Lambert, T-Mar Industries

Hunter Harrill, University of Canterbury

Brian Tuor, Cable Logging Specialist

Rien Visser, University of Canterbury

Jeffrey Wimer, Oregon State University

CONTACTBrian Boswell, R.P.F.Senior ScientistFibre [email protected]

FPInnovations Page i

Table of contents

1. Introduction..................................................................................................................................... 1

2. Basics of Wire Rope ....................................................................................................................... 1

Steel grades and finishes ................................................................................................................... 1

Construction....................................................................................................................................... 2

3. End connectors............................................................................................................................... 5

4. Failure mechanisms........................................................................................................................ 8

Bending Fatigue................................................................................................................................. 8

Abrasion........................................................................................................................................... 10

Corrosion ......................................................................................................................................... 10

Tensile overload............................................................................................................................... 10

Shear breaks.................................................................................................................................... 10

5. Wire rope comparisons................................................................................................................. 10

6. Inspections and preventative care ................................................................................................ 12

Frequency of inspections ................................................................................................................. 12

Visual inspection .............................................................................................................................. 12

Electromagnetic inspection............................................................................................................... 15

7. Overloading: exceeding the safe working load, endurance limit, or elastic limit............................. 17

8. Temperature damage ................................................................................................................... 18

Heat ................................................................................................................................................. 18

Cold ................................................................................................................................................. 18

Fittings and Chains .......................................................................................................................... 19

Detecting and preventing heat damage............................................................................................ 19

9. Rope replacement criteria............................................................................................................. 20

10. Service life ................................................................................................................................ 20

11. Winch-assist manufacturer specifications.................................................................................. 22

12. Learnings from winch-cat operations in the ski industry............................................................. 23

13. WorkSafeBC regulations ........................................................................................................... 27

14. Worksafe New Zealand ............................................................................................................. 30

15. Wire Rope Storage and Handling .............................................................................................. 31

15. References Cited ...................................................................................................................... 33

16. Appendix: Wire rope specifications and discard information...................................................... 36

FPInnovations Page ii

List of figures

Figure 1. Construction types .................................................................................................................. 2

Figure 2. Core types .............................................................................................................................. 2

Figure 3. Compacted rope ..................................................................................................................... 4

Figure 4. Triangular wire rope strand ..................................................................................................... 5

Figure 5. X-Chart for wire rope............................................................................................................. 12

Figure 6. Crown and valley wires ......................................................................................................... 14

Figure 7. Example of birdcaging damage to wire rope ......................................................................... 15

Figure 8. Example of raw data from EM scanning................................................................................ 16

Figure 9. Example of sensor head and console for electromagnetic wire rope inspection system........ 16

Figure 10. Service life curve versus D/d ratio....................................................................................... 21

Figure 11. Relative service life curve ................................................................................................... 22

Figure 12. Winch-cat pushing snow uphill ............................................................................................ 23

Figure 13. Testing winch-assist for forestry with a winch-cat and a forwarder ...................................... 23

Figure 14. Construction of Fatzer rope................................................................................................. 24

Figure 15. Wire rope spooler................................................................................................................ 26

Figure 16. Examples of rock anchors used for winch-cats ................................................................... 27

Figure 17. Correct and incorrect spooling ............................................................................................ 31

List of tables

Table 1. Wire rope grades ..................................................................................................................... 1

Table 2. Wire rope core types ................................................................................................................ 2

Table 3. Lay types ................................................................................................................................. 3

Table 4. End connectors and efficiency ................................................................................................. 7

Table 5. Effect of bending on strength ................................................................................................... 9

Table 6. Minimum factors of safety for wire rope.................................................................................. 17

Table 7. Example of temperature derating for steel wire rope .............................................................. 18

Table 8. Temperature range and deratings for rope terminations......................................................... 19

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1. INTRODUCTION

Innovations in forest harvesting methods have allowed ground-based harvesting machines andextraction machines to operate safely on steep terrain that was previously inaccessible. This has beenaccomplished by connecting the machine to an anchor using wire rope, referred to as winch-assist. Thepractice, while relatively new to North America, is gaining acceptance in British Columbia. There is ademand for information on all aspects of these new harvesting systems to ensure safe operations. Thisreport focuses on the wire rope component of winch-assist systems. The first sections of the reportcover wire rope basics that are common to all applications while the later sections provide some winch-assist specific information where it is available.

2. BASICS OF WIRE ROPE

The first wire rope was invented around 1830 in Germany by mining engineer Wilhelm Albert. It was 18mm in diameter and consisted of three strands of four wires each. One of wire rope’s biggestadvantages over the chains which it replaced was that its imminent failure is indicated in advance bysingle broken wires while chains gave little warning before failure (Verreet, 2002).

The structure of wire rope consists of three components: wires, strands, and a core (Wire RopeTechnical Board, 2005). Wire rope nomenclature often uses abbreviations to represent the varioustypes and grades of each component. It is important for the user to identify what type of rope is neededfor their application.

See Appendix for typical wire rope specifications for ropes commonly used in cable logging.

Steel grades and finishesThe wire is typically constructed from high carbon steel and can come in a number of grades. (Table 1)

Table 1. Wire rope grades

Wire grade Typical abbreviationMinimal Tensile

Strength(N/mm2)

Plow steel PS 1570Improved plow steel IPS 1770Extra improved plow steel EIPS or XIS or XIP 1960Extra extra improved plow steel EEIPS 2160

The higher grade steels have higher carbon content so are stronger but are less flexible and canfatigue faster. EIPS is the most commonly used grade today. IPS and EIPS are both commonly used inlogging. While EIPS has higher strength IPS is often preferred as EIPS is more susceptible to burningand can fatigue faster. Another advantage is the IPS rope looks worn out when it is worn out but EIPSstill looks good when it is worn out. EIPS isn’t desirable for chokers and strawlines because it kinksmore easily than IPS (US Department of Agriculture, 1978). EIPS and higher grades offer theopportunity to design machines that provide higher load rating using smaller diameter ropes.


Wires come in a variety of finishes. The most common wire rope is uncoated or “bright”, but it can begalvanized with zinc or zinc/aluminum alloy to improve corrosion resistance. Normal galvanized ropehas 10% less strength than bright rope of the same size and type. There is also drawn galvanized ropewith a thinner coating and strength equal to an equivalent bright rope. Stainless steel rope is veryresistant to corrosion so is used in very harsh conditions such as salt water and acidic environments.

ConstructionRopes are groups of strands arranged around a core. Strands are groups of wire arranged in ageometric pattern (Wire Rope Technical Board, 2005). The wire ropes typically used in logging havestrands that are formed from wires grouped in a helical shape. Strand constructions are defined by theircombination and arrangement of wire sizes. The common strand constructions are: ordinary or singlelayer, seale (S), warrington (W), and filler wire (FW). (Figure 1) There are also combined patterns likewarrington seale (WS).

Figure 1. Construction types(Suwan, n.d.)

Core

The core of the wire rope supports the strands as they are subjected to bending and loading. It can beconstructed from steel, natural fibres, or synthetic fibres. Each core type has a commonly usedabbreviation. The core types described in Table 2 are the three most frequently used and are illustratedin Figure 2.

Table 2. Wire rope core types

Core type Description Typicalabbreviation

Wire strand core Single strand with 7 or 19 steel wires WSCIndependent wire rope core Steel wire rope w 7x7 construction IWRCFibre Core i.e. Hemp, sisal, manila, polypropylene FC

Figure 2. Core types(Shah, n.d.)


Steel cores provide 7 to 12% more strength, are more heat resistant and more resistant to crushingcompared to a fibre core. Weight is increased by about 10% with steel cores. A fibre core providesmore flexibility and cushioning to shock loading and can store more lubricant compared to a steel core.

Lay

Lay has three meanings in wire rope. 1) It is the length of wire rope for one strand to completely spiralaround the rope. 2) It indicates the direction the strands rotate or lay in the rope. 3) It describes how thestrands are assembled in the rope relative to the wires.

Strands can be laid in two directions about the core: left or right lay. Additionally, the direction of thewire laid within the strand relative to the direction of the strand lay of the rope is specified as eitherregular lay or lang lay. Regular lay ropes have the direction of the strand opposite to direction of theindividual wires. Whereas, lang lay ropes have the wires and strand lays going in the same direction.Regular lay ropes do not kink or untwist easily and are easy to handle. Lang lay ropes are moreresistant to abrasion and fatigue but are more likely to kink and untwist.

Ropes which have alternating regular lay and lang lay strands are called alternate lay ropes. Each ofthe different lay types have an abbreviation commonly used to differentiate it. (Table 3)

Table 3. Lay typesLay type Typical abbreviation

Right regular lay RRLRight lang lay RLLLeft regular lay LRLLeft lang lay LLLRight alternate lay R-ALTLeft alternate lay L-ALT

Ropes constructed with regular or lang lay have different advantages and disadvantages. Regular laycan resist rotation better than lang lay, with lang lay requiring both rope ends to be fixed while underload. Regular lay has better resistance to crushing, while lang lay is susceptible to crushing whenoperated on smaller than optimally sized sheaves. Lang lay has better fatigue resistance than regularlay. Lang lay’s longer exposed wires and lower axial bending of outer wires gives it 15% to 20% betterfatigue resistance compared to regular lay. Lang lay also has better abrasion resistance compared toregular lay because of the higher pressure experienced by regular lay rope when it is under load.

Nomenclature

Wire rope nomenclature can seem complex. When referring to a specific construction of wire rope, fourattributes are given: number of strands, number of wires per strand, core type, and construction type.The construction type is the geometric arrangement of the wires. An example of specific constructionswould be 6 x 41 Warrington Seale IWRC, which has 6 strands, 41 wires per strand, a Warrington Sealeconstruction type, and has an independent wire rope core. Lay type may also be given.


One source of confusion is the similarity of wire rope classification and specific construction names.Classifications can have specifications that seem to indicate a certain number of strands and number ofwires per strand, yet actually do not. As stated in the Wire Rope Users Manual (2005), “ropes in aclassification have the same minimum breaking force and approximate weight per foot”. In comparison,specific constructions usually have names which better describe their properties.

Sometimes a supplier will omit some of the details of a specific construction. This regularly happensand is considered common knowledge in the industry. If there is no stated lay direction or type, the ropeis assumed to right regular lay. If there is no finish stated, the rope is assumed to be uncoated. If thereis no indication if the rope was preformed, the rope is assumed to be preformed.

6 X 19 class (6 strands with 16 to 26 individual wires per strand) ropes in a 6 x 26 IWRC configurationare commonly-used ropes in cable logging because they provide a compromise of resistance tobending fatigue (optimized by many smaller wires) and resistance to abrasive wear (optimized by fewerbigger wires).

Special constructions

There are a number of special wire rope constructions which are modified to have characteristics thatare different than standard constructions. For example, rotation resistant ropes are designed to notrotate. They require special handling and their internal components wear faster than standard rope.

Compacted rope

Compacted wire ropes have part of their construction flattened to increase their densities. Thisincreases their breaking strength for a given diameter. Compacted ropes also have better abrasion andcrushing resistance however they have worse bending fatigue resistance. There are two types ofcompacted ropes: strand compaction and swage compaction. (Figure 3) In strand compaction, eachstrand is compacted, flattening the outer wires before the rope is formed. This results in a smoothersurface on the rope. In swage compaction or swaged rope, the rope is formed first and thencompacted. Swaged ropes may develop broken wires internally before they develop externallycomplicating inspection. There is also double compacted rope where the individual strands arecompacted and the whole rope is compacted.

Figure 3. Compacted rope(Shah, n.d.)

Triangular rope


Triangular wire rope (also referred to as flattened wire rope) is a construction where each strand’s wireswrap around a triangular shaped centre, which imparts a triangular shape to the strand. (Figure 4) Theresulting structure has about 15% more steel in the cross-section and a smoother, relatively flat ropesurface. This form gives the wire rope more surface contact with sheaves and higher strength,crushing resistance, and abrasion resistance compared to standard rope. They perform especially wellon applications with heavy loads and slow speeds and are used as haul ropes in the mining industry.

Figure 4. Triangular wire rope strand(Shah, n.d.)

Plastic filled rope

Plastic filled wire ropes have their voids filled with plastic, which extends to the outer circumference.The process improves the ropes resistance to corrosion and bending fatigue. Their breaking force issimilar to non-plastic filled rope. Plastic filled ropes have been tried in NZ and the PNW and arecurrently used in Europe for some logging applications.

3. END CONNECTORS

While special consideration is given to wire rope integrity in this guide, it should be noted that a riggingsystem is only as strong as the weakest link. In fact, the most vulnerable part of a winch-assist riggingsystem may be the termination of the rope where it transitions to a connection point. As such, thebreaking strength of the system should be downrated according to the efficiency of the weakestconnector. See Table 4 for a list of end connectors and their efficiency.

Efficiency

An 80 percent efficient end connector means that only 80 percent of the wire rope’s breaking force isavailable. The design factor or factor of safety must be applied to this reduced breaking strength todetermine the actual working load that can be used on the end connector.

Common end connectors

The most common end connectors used in winch-assist operations are:

Spelter socket: Molten zinc or an epoxy compound is poured into the socket to bond the wire rope intothe fitting. Spelter sockets are the strongest end connection currently available. However, they can onlybe installed at a workshop, making them impractical for field replacements. Installation with resin can


be done in the field by a trained technician; however the process is time consuming: it may take hoursfor the resin to set.

Wedge sockets: In wedge sockets, the cable is looped around a wedge which is inserted into a socketand held in place by tension. They are common in winch-assist operations due to their fast and easyfield installation. Incorrect installation can result in uneven loading and a significant reduction instrength.

Flemish eye: Also called farmer’s eye, has a high efficiency when fitted with a ferrule (92-95%), but thiscan only be done in a workshop. Without the ferrule, it serves as a quick temporary splice. Thimblesadd strength and prevent rope damage.

Soft eye with pressed ferrule: A soft eye is often fitted on the wire rope by the supplier. It provides astrong connection (90-95%) however it must be fitted at a workshop so it is not a practical option whenreplacements are needed in the field. Ferrules also tend to fail more frequently if dragged on the grounddue to their material composition. As with spliced eyes, thimbles add strength and prevent ropedamage.

Spliced eye: Also called logger’s splice, although there are several other types of splices possible, it’sthe most common end connector in winch-assist harvesting operations due to its ease of installation inthe field and popularity in cable logging operations. It is also easy to pull through a block and is easy toinspect. However, it is not the strongest connector (~80% efficiency) available. Note that using athimble adds strength and prevents eye deformation.

Split wedge ferrules: Also commonly used in winch-assist operations due to their fast installation time(can be done in minutes) and their popularity in cable logging operations (most loggers are familiar withthis connector). They are lightweight and easy to handle, however there is limited knowledge of theirstrength. If not fitted correctly, they can cause overloading on one strand and frequent wire breaks orrope failure. Note that split wedge ferrules should not be used with swaged ropes.


Table 4. End connectors and efficiency

Attachment or splice Efficiency (% of ropestrength)

Spelter and swaged socket

100

Wedged socket

70-90

Cable clips

80

Flemish eye (no thimble) with pressed ferrule

Flemish eye (with thimble) with pressed ferrule92-95

(+6 with thimble)

Soft eye (no thimble) with pressed ferrule

Hard eye (with thimble) with pressed ferrule90-95

(+6 with thimble)


Attachment or splice Efficiency (% of ropestrength)

Spliced eye and thimble

80-88

Spliced eye without thimble

<80

Swaged ferrule

80-90

Split wedge ferrule

unknown

4. FAILURE MECHANISMS

Wire rope has many routes to failure according to Canadian Centre for Occupational Health and Safety(2013). The most common are overloading, fatigue, abrasion, distortion, kinking, heat, and corrosion.However, there are a number of methods to prevent or mitigate the damage caused by these failureroutes.

As a wire rope is worked it undergoes normal and expected wear that will eventually lead to failure.Under load, the rope will stretch causing it to rub against the drum, sheaves and any other point ofcontact. The internal structure of the rope will also experience rubbing. There are five mechanismswhich will eventually cause a wire rope to fail: bending fatigue, abrasion or mechanical wear, corrosion,tensile overload, and shear breaks. (Verreet & Ridge, 2006a)

Bending FatigueAny bending of the rope will cause wear and eventually result in broken wires. The most frequentsource of bending is where a rope passes over a sheave or drum. The difference in diameters of theinside and outside of a rope passing over a sheave results in stretching. Wear from bending fatigue canworsen significantly if the rope is used inappropriately. The diameter of the sheave used is an importantfactor. As the ratio of sheave diameter to rope diameter decreases, wear caused by the bending


increases exponentially. Keeping the rope sufficiently lubricated is important as it can mitigate internalwear from wires and strands bending and adjusting. Bending direction should be kept consistent. Oncethe rope has been cycled, the bending direction is set. If the rope is reinstalled and the original bendingdirection is changed, subsequent use will increase its wear rate.

The sheave itself can damage the rope it supports if the sheave is damaged or does not have acompatible groove shape. A damaged groove which has become corrugated will damage a rope. If thegroove is too narrow it can pinch the rope as it passes and cause damage. A groove that is too narrowalso prevents the rope’s internal structure from adjusting which imparts wear to the rope. Also, asheave with a groove that is too wide will not fully support the rope as it passes and will hasten wearand fatigue.

Fatigue resistance is increased in wire rope design by more wires, smaller wires, fibre cores, and langlay.

Loss of strength due to bending

Any curved surface that a wire rope travels around will affect the rope’s strength. The angle of benddoes not have to be large to have a significant impact. For example, a curve diameter to wire ropediameter ratio of 1:1 will decrease the strength of the rope by 50%.

When considering the use of a steel wire rope around a minimum D:d ratio (sheave diameter to ropediameter ratio), it is generally accepted that at below 4:1 the effect on the strength of the rope needs tobe considered. Permanent distortions within the rope will occur when using ratios of 10:1 and less anda minimum ratio of 16:1 is recommended for a rope operating around sheaves. However less thanoptimal sheave sizes are generally used in cable logging to reduce their weight because a worker mustbe able to carry and install the sheaves (blocks) in the forest.

The effect of different sheave to rope diameter ratios on rope strength is also illustrated in Table 5.

Table 5. Effect of bending on strength(Harrill, 2016)

Sheave/Rope Diameter Ratio Efficiency of Rope

10 times 79%

12 times 83%

14 times 86%

16 times 88%

18 times 90%

20 times 91%

24 times 93%

30 times 95%


There is also a strong relationship between wire rope life and a rope’s contact pressure on a sheave.The higher the contact pressure ratio the lower the number of bending cycles until rope failure.Increasing sheave diameter can increase rope life by reducing the bearing pressure ratio.

AbrasionAbrasion occurs when the wire rope rubs against an external source (Verreet & Ridge, 2006a). Thesource could be a different section of the same rope, a component of the rigging, or somethingunrelated to the machine such as the ground, a rock outcrop, or sand/silt that gets deposited betweenthe strands or wires. In some cases, abrasion can be mitigated with proper lubrication and using theappropriate rope design. New rope will experience a higher abrasion rate than rope that has been inservice for long enough to wear down prominent material. The abrasion rate subsides when the rope’sbearing surface has increased (Verreet & Ridge, 2006a). If abrasion is occurring at a sufficient rate, itcan prevent fatigue cracks, because the diameter of the rope decreases too quickly for cracks to form.

Abrasion resistance is increased in wire rope design by fewer and larger outer wires, higher carboncontent in the metal, and lang lay.

CorrosionCorrosion on wire ropes occurs because of reaction with oxygen (Verreet & Ridge, 2006a). Surface rustor deep pitting can occur. This results in a loss of rope strength and flexibility, which can lead to fatiguecracks forming more quickly. This can be minimized by employing a galvanized or plastic coated rope,and lubrication.

Tensile overloadWhen the rope experiences an axial load that overwhelms its strength, it undergoes tensile overload(Verreet & Ridge, 2006a). All wire rope failures will be in part due to tensile overload.

Shear breaksA shear break will occur if a wire rope undergoes compression at the same time as it undergoes a largetensile load (Verreet & Ridge, 2006a). The compression of the rope lowers its strength. In other words,a shear break will occur under lower loading conditions than those required to cause tensile overload ina similar rope.

5. WIRE ROPE COMPARISONS

When choosing a wire rope for a given task, the five failure mechanisms above should be taken intoconsideration.

1. Tensile overload (minimum breaking force)a. Static load is determined by: Dead load + accelerate/decelerate loads + shock loads +

sheave bearing efficiency loss from bendingb. Static load is multiplied by the design factor to determine the minimum breaking force

that is required2. Bending fatigue

a. The more acute the bend, the greater the fatigue


b. As rope speed increases, so does fatiguec. Resistance is improved with

i. More outer wires per strandii. Smaller wiresiii. Fibre coresiv. Lang lay

3. Vibrational fatigue resistancea. Fatigue caused by vibrations along rope lengthb. Energy is transmitted to the rope at end fitting or contact points

4. Abrasion resistancea. External from rubbing the outside of the rope against surfaces or objectsb. Internal from rubbing as adjustments to loading or bending occurc. Reduces strength because it degrades the wiresd. Resistance is improved by lang lay, fewer larger outer wires, and higher carbon content

steel5. Crushing resistance

a. Usually occurs because of improper winding on drumb. Resistance is improved with

i. Fewer outer strandsii. Larger outer wires in strandsiii. IWRCiv. Regular layv. Compaction of strandsvi. Compaction of ropevii. Higher carbon contentviii. Six strand ropes have greater lateral stability than 8 strand ropes

Of the five, bending fatigue and abrasion are often the biggest concern. There is an inverse relationshipbetween bending fatigue resistance and abrasion resistance. This leads to a compromise betweenthese two attributes in every application as illustrated in Figure 5.


Figure 5. X-Chart for wire rope(Harrill, 2016)

6. INSPECTIONS AND PREVENTATIVE CARE

Inspection is essential to maintain wire rope. The objectives are to 1) observe normal deterioration so arope can be retired before it becomes a hazard and 2) detect unexpected damage or corrosion. Twotypes of inspection are available: visual and electromagnetic. A rope must not be under load duringinspection. It should be “relaxed”.

Frequency of inspectionsThe longer a rope has been in use and the more severe its use, the more thoroughly and the morefrequently it should be inspected. Wire rope in continuous service should be inspected during operationand at least once a week (Infrastructure Health and Safety Association, 2012).

Visual inspectionDetailed guides for visual wire rope inspection are available in Tech Report No. 107 by Union WireRope (Union Wire Rope, 2009) and ISO 4309 (ISO, 2010).

Visual and tactile inspections only provide information on the outer wires and only on the visible portionof outer wires which is only about 20% of the cross sectional area (Verreet & Ridge, 2006b). If the mainsource of wear is internal rather than from an external source, such as a sheave, the visual inspectionprovides little benefit.


Figure 6. Crown and valley wires(Wirerope Works Inc., n.d.)

Wires on the outer perimeter of the rope must be checked for wear and abrasion. If a rope’s outer wiresshow abrasion of more than 33% of their diameter, the rope must be retired (Workplace Safety North,2011).

Stretching from its original length is normal for wire rope when it is first put into service. The effect ispermanent and is due to strands adjusting and fitting into their designed position as a load is applied(Workplace Safety North, 2011). Rope with 6-strand constructions can be expected to stretchapproximately 6 inches per 100 feet. Ropes with 8-strand constructions are expected to stretch 10inches per 100 feet. However, if a rope is found to have stretched beyond these lengths, it should beretired.

Measure the rope diameter and compare to its original diameter. Measure and record a new rope’sdiameter then keep records of subsequent inspections.

It is possible to visually inspect the rope interior by using a marlin spike. Insert the spike under twostrands and rotate it to open the rope and expose the interior. While this may not be practicaleverywhere it can aid in the inspection of a suspect section.

Just like any iron based product, wire rope can be subject to corrosion. Proper lubrication can help withprevention. However, if signs of corrosion, such as pitting or rust near connections are found on therope, the user should consider retiring it (Workplace Safety North, 2011) or the section affected shouldbe removed immediately.

If the rope is not properly supported, crushing can occur. If the user can see any visibly crushed,flattened, or jammed strands, the rope need to be replaced (Workplace Safety North, 2011).

In addition to the 5 areas listed above to focus on during an inspection, there are a number of specialcase defects that the inspector should be watching for: bird-caging, kinking, and core protrusion.

When a wire rope shows outer strands protruding out from their usual position adjacent to the core, thisdefect is known as bird caging. Bird caging is caused by a sudden release of tension and the resultingrebound. The rope’s outer strands become longer than its core over a short section (Verreet & Ridge,


2006c). The lengthening of the outer strands is usually due to twist unwinding the rope. Thelengthening of the outer strands is usually slight and happens over a long section of rope. However,through the constraining action of a sheave, the extra strand length is collected and brought to a shortsection, causing the strands to noticeably stand-out from the core. (Figure 7) Rotation resistant rope ismore susceptible to bird caging because the opposite lay direction of the rope’s strands and core causetwist to lengthen the strands while simultaneously shortening the core. If bird caging is observed, therope should be retired or the section affected should be removed immediately.

Figure 7. Example of birdcaging damage to wire rope(Convergence Training, n.d.)

If a load is applied to a rope containing a loop, the loop will collapse and cause a kink (WorkplaceSafety North, 2011). The section of the rope containing the kink must be removed or the rope must bereplaced.

A wire rope’s core will protrude from the between the strands if the rope has been subjected to shockloading or torsional imbalance (Workplace Safety North, 2011). The rope must be retired if this defecthas been found.

Electromagnetic inspectionWire rope can also be inspected with electromagnetic (EM) scanning technology. This method candetect internal rope defects unseen in visual inspections such as broken internal wires and internalcorrosion. (Figure 8) It is used for testing of cables used for ski lifts and other industries. It has beenused experimentally in the forest industry to inspect skyline cables (Macey, 1998). Adapting thistechnology to winch assist systems could improve rope replacement decisions.

The technology functions by monitoring magnetic flux leakage using three parameters: LMA (loss ofmetallic cross section), WRR (wire rope roughness), and LF (localized faults). The LMA signalmeasures loss typically caused by corrosion and abrasive wear for the entire cable length. Ropes aretypically retired when LMA exceeds 10%. WRR is an additional software analysis of the LMA signalthat computes the total surface roughness of all wires in the rope to quantify single and clustered


broken wires and corrosion pitting. The LF signal provides data on localized flaws for qualitativelylocating single broken wires and corrosion pitting.

Figure 8. Example of raw data from EM scanning(Macey, 1998)

EM wire rope inspection systems consist of a sensor head and a signal processing and recordingconsole. The sensor heads come in a range of sizes for testing ropes up 165 mm in diameter, weighingup to 75 kg. A unit suitable for testing the largest ropes used in winch assist systems weights about 8kg. (Figure 9)

Figure 9. Example of sensor head and console for electromagnetic wire rope inspection system(NDT Technologies, 2012)

EM wire rope inspection is available in BC from Inter-Mtn Testing located in Kelowna, telephone: 250-491-4250. The cost is $150/h for testing equipment and labour plus any travel expenses. For example,a 6 h day to complete a test would be $900. A very rough estimate for onsite testing, report, and travelcosts could be about $2000. However Inter-Mtn normally schedules one or two week long trips to


various areas of the province to service multiple clients to reduce travel expenses for individual clients.(Muirhead, 2017)

7. OVERLOADING: EXCEEDING THE SAFE WORKING LOAD, ENDURANCELIMIT, OR ELASTIC LIMIT

The elastic limit for a wire rope is the load limit where the rope will return to its original length after theload is removed. If it is exceeded the rope is damaged immediately with a permanent reduction intensile strength and should be taken out of service. The rope now has the potential to fail at smallerloads, even at loads less than its rated safe working load (SWL). The elastic limit varies by rope typebut occurs at about 60 to 65% of a rope’s rated breaking strength in the ropes commonly used forlogging. The endurance limit of wire rope occurs at 50% of the rope’s rated breaking load. If theendurance limit is exceeded the rope’s lifespan will be reduced.

A rope’s safe working load (SWL) depends on its design factor or factor of safety (FS) for its applicationand is determined by the design engineer or an applicable standard. Table 6 shows the wire rope FSfor a range of applications and rope speeds in feet per minute (fpm). Currently there is no establishedFS standard for wire ropes used in winch-assist systems. In cable logging planning, a 3:1 FS iscommonly used for skyline payload analysis. Yarders in BC are not required to be rated for a maximumload however their cable sizes must be specified by the manufacturer. Workers should always keepwell clear of the moving lines and payloads.

Table 6. Minimum factors of safety for wire rope(Shingley & Mitchell, 1983)


An operator should always operate a cable system within the design’s SWL. Load monitoring isavailable on most winch assist systems and recording of overloading incidents is available on somesystems. Regular checking of any overload records should be part of the rope maintenance. If the SWLis exceeded regularly then the operating procedures and/or rope specification should be re-evaluated.

Research on several different winch assist systems showed that the SWL was exceeded up to 2% ofthe time during normal operations. Loading sometimes exceeded the SWL by over 25% (Visser, 2016).Research also showed that high shock loading occurred most often during machine movement. Careshould be taken to keep all machine movements as smooth as possible and avoid shock loading. Somewinch-assist manufacturers have developed software for their equipment to help alleviate shock loadingby facilitating a more gradual application of the winch brakes.

In winch-assist systems the capacity of the entire system should be considered as the rigging system orfittings can be the weakest link.

8. TEMPERATURE DAMAGE

HeatWire rope can be damaged by exposure to extreme temperatures. Rubbing against trees and stumps,for example, can produce high temperatures and potential rope damage. Fibre core ropes will dry outand break and should not be used if temperatures exceed 82°C. IWRC ropes have a higher operatingtemperature range up to 204°C. IWRC Rope will require derating of its minimum breaking strength attemperatures above 93°C (Table 7) however it is not recommended to use steel core ropes attemperatures above 204°C. Ropes should also not be used above the drop (melting) point of itslubricant. For example, Jetlube specifies a maximum operating temperature of 175°C for its “WRL” wirerope lubricant.

Table 7. Example of temperature derating for steel wire rope(Bridon, n.d.)

Operating temperature range(°C)

Derating(% of minimum breaking strength)

0 - 93 093 - 204 10

204 - 316 25316 - 427 35

>427 Do not use

ColdExtreme cold also affects wire ropes. Rope lubricants and synthetic filling or coverings may becomeineffective. Literature from manufacturers set minimum operating temperatures for IWRC wire ropefrom -40°C to - 51°C. Jetlube’s WRL’s minimum operating temperature is -32°C.


Fittings and ChainsRope end terminations also have temperature operating limits which may be more limiting than those ofwire rope. Limits depend on the type of end termination, the fitting’s material, and the type of rope core.Ferrules and splices can be used from -40°C to 100°C before it is necessary to derate their workingload. Sockets can be used from low temperatures of -40 or -50 °C to high temperatures of 80 or 120°C(depending on the material) without derating (Table 8).

Table 8. Temperature range and deratings for rope terminations(Certex, n.d.)

Chains are an integrated component of many winch-assist systems and also have temperatureoperating limits. At extremely low temperatures, the steel becomes brittle and may fracture. Suddenloading should be avoided at temperatures below -18°C (-0°F). The highest temperature that chainshould be exposed to is 260°C (500°F).

Detecting and preventing heat damageRubbing against trees and stumps can produce high temperatures and potential rope damage. Look forburn marks or changes in colour on the rope and charring on wood. Charring of wood on trees andstumps where rope has rubbed is an indication of possible heat damage to a rope. Wood chars at 120to 150°C depending on species and ignites at 190 to 260°C with decayed wood igniting at 150°C.(Cafe, n.d.) Heat guns and infrared cameras can also be used to instantaneously detect wire ropetemperature and potential damage. Heat damage to the wire rope from winch assist operation has notbeen verified however and would likely be confined to a very minimum depth. Research is needed toconfirm. However the outside layer of steel in the outside wires may experience rapid heating andcooling causing the wires to become hard and brittle (martensite) which will lead to premature crackingand fatigue failures.

Winch-assist systems should be rigged and positioned to avoid rope contact with objects or the ropeitself. Anchor-machine mounted winch systems have a moving line under tension and will incur linedamage from friction contact and abrasion from the moving line(s). Static line systems will also receive


diameters, reverse bends, lubrication, the system’s design factor, and the number of strands in therope.

As mentioned earlier, service life is greatly influenced by the D/d ratio (bending diameter(D) to ropediameter(d) ratio). A rope’s fatigue resistance is reduced more with smaller diameter bends. Oneshould consider the smallest bend in the system when determining its D/d ratio including drums,sheaves, and fairlead rollers. If stumps, trees, or blocks are used to redirect the rope, their diametersshould also be considered. The effect is illustrated in Figure 10 where service life is reduced from 100%to 76% (only a 26% reduction) if the D/d ratio is 55, but is reduced from 100% to 25% for a 75%reduction in service life when the D/d ratio is 30, for example. In cable logging, manufacturersrecommend a ratio of 30:1 (sheave size to line diameter) but the industry standard is 20:1(WorkSafeBC, 2006). Additionally, a rope’s breaking strength is also greatly reduced by a small D/dratio as shown above in Table 5.

Figure 10. Service life curve versus D/d ratio(Wirerope Works Inc., n.d.)

Reverse bends greatly reduce rope life and should be avoided. A reverse bend will fatigue a rope 2 to 7times as much as a simple bend. (Verreet, n.d.)

Proper lubrication will increase rope life while poorly lubricated rope has less fatigue resistance and willwear internally as the wires move against each over. However lubricating a rope externally can bedetrimental if the rope is normally in contact with soil during use. This is because particles will adhere tothe lubricant and cause abrasion to the rope and sheaves. Rope lubrication is discussed in more detailin Section 15 Wire Rope Storage and Handling.

The design factor also affects rope life. (Figure 11) This is because the rope with a lower design factorwill be operating at a higher tension relative to its breaking strength. Figure 11 illustrates that droppingthe design factor from 5 to 3 will reduce a ropes service life from 100% to 60%


night in the dark. Also they generally work on smoother and slipperier surfaces (snow and ice)compared to feller-bunchers in BC.

And some similarities: They are mainly used as one machine systems with the winch mounted on themachine like the Climbmax, Herzog, or Haas systems. Occasionally two winch-cats will be joinedtogether to extend the system`s range. This arrangement is closer to the two machine systems used inforestry where a machine up the hill serves as an anchor. They sometimes anchor to trees and theysometimes used other trees to redirect the rope (siwash) as is done in forestry operations. Their winchcan be capstan type (like a Herzog or Twinch) or direct drum type (like a Climbmax or T-Mar).

A winch-cat’s main job is using their blade to push snow up the hill to replenish the snow that skierspush down the hill as they ski. They then use their tiller to smooth out the snow surface on their finalpass.

The winch-cat’s rope travels in and out through a movable boom. The winch and boom are mounted ona continuous rotation turret so the machine can travel in any direction while the rope maintains a directpull but does not interfere with the machine’s tracks while it is driving. Rope tension is maintainedautomatically similar to most forestry systems. The machine is designed so it can’t outrun the winch.The tracks will automatically slow down if necessary. This keeps the cable in the air and not on theground or snow surface and prevents shock loading.

Cable

The capstan winch machines require a special wire rope, like the one made by Fatzer in Switzerland(Figure 14). It is a complex, multi-layered, galvanized, compacted rope. The outer layer is wound in theopposite direction of the inner layer. It is also made of varying sizes of wires and composed of 253wires in 19 strands for a very flexible construction.

Figure 14. Construction of Fatzer rope(Fatzer, n.d.)

The rope’s diameter is 11 mm and its breaking strength is 115 kN (12 tonnes). With a working load of45 kN (4.6 tonnes), the factor of safety is 2.6. The capstan winches at Whistler/Blackcomb use 1050


Figure 15. Wire rope spoolerLine twist

Line twist is a big concern because of the patterns that the winch-cats drive. It is necessary to regularlyrelease twist that builds up in the line as a swivel is not permitted with this type of rope. After every 100hours of winch operation a “cable relax” is performed. The entire line is unspooled and taken off thedrum. The end is left connected to the anchor and the tension works its way out of the cable. It is alsomanually untwisted by hand if necessary. It is then checked in three places. If it remains twisted theoperator will repeat the process, spooling it and releasing it a few more times until it is neutral again.

Line life

While some literature indicated that the lifespan for wire rope on winch-cats was up to 1,200 h and10,000 capstan passes, Whistler/Blackcomb has found their normal wire rope life is 600 hours of winchtime.

Line twist can substantially shorten the rope’s life. When a rope is twisted, it doesn’t spool onto thedrum properly. There will be high wraps and it will tend to jump off the capstan. A neutral cable spoolswell and lasts longer.

The design of winch-cat capstans have evolved over time and their diameters are now larger on thenewest models. This has increased rope life by reducing the amount the rope must bend.

Anchors

Most of the permanent anchor points are rock bolts. (Figure 16) The bolts are connected to anextension cable that can be reached in deep snow. Some have been raised up with a tower support sothe cable does not rub on a terrain point that breaks over sharply.


Figure 16. Examples of rock anchors used for winch-cats

Line Breaks

The winch-cats do experience wire rope failures sometimes. The machine will slide and the operatorwill usually get the blade lowered which digs into the snow and stops the slide. Sometimes the machinewill slide further until it reaches a less steep area and stops. Sliding did not seem to be a big safetyconcern as the ski runs where the machines generally work are located where there is some runout andno cliffs below. The machine manual specified that “operation is prohibited on slopes without sufficientflat runout at bottom”. The bigger concern in a slide seemed to be the potential for machine damage.

When a line breaks it usually starts with abrasion, from sawing across a rock, for example. Breakshappens quite quickly when this occurs. They have also experienced breaks when an operator hashooked to an anchor and then driven away without activating the winch.

13. WORKSAFEBC REGULATIONS

WorksafeBC has no regulations specific for wire rope use on winch assist systems but does haverigging regulations that may serve as helpful guidelines and may be enforceable in somecircumstances. Below is some of the applicable information. For more details see Section 15 of theregulations (WorkSafeBC, n.d.). Examples of wire rope and rigging regulations include:


15.6 Design factors

Component Minimum design factor

Alloy steel chain sling 4

Wire rope sling 5

Synthetic web sling 5

Chain fittings 4

Wire rope sling fittings 5

Other fittings as specified by manufacturer

Non-rotating wire rope as specified by manufacturer but not less than 5

Conventional wire rope 5

The design factor for any rigging assembly used to support workers must be at least 10.

15.25 Wire rope rejection criteria

Wire rope must be permanently removed from service if:(a) in running wire ropes, there are 6 or more randomly distributed wires broken in one rope lay or 3 ormore wires are broken in one strand in one lay,(b) in stationary wire ropes, such as guylines, there are 3 or more broken wires in one lay in sectionsbetween end connections, or more than one broken wire within one lay of an end connection,(c) wear, or the effects of corrosion, exceed 1/3 of the original diameter of outside individual wires,(d) there is evidence of kinking, bird-caging or any other damage resulting in distortion of the ropestructure,(e) there is evidence of heat or arc damage, or(f) there are reductions of normal rope diameter, from any cause, in excess of

(i) 0.4 mm (1/64 in) for diameters up to and including 8 mm (5/16 in),(ii) 1 mm (3/64 in) for diameters greater than 8 mm (5/16 in) up to and including 19 mm (3/4 in),(iii) 2 mm (1/16 in) for diameters greater than 19 mm (3/4 in) up to and including 29 mm (1 1/8in), or(iv) 3 mm (3/32 in) for diameters greater than 29 mm (1 1/8 in).

15.26 Nonrotating wire rope

Wire rope with nonrotating construction must be removed from service if:(a) the rejection criteria in section 15.25 are met,(b) there are 2 randomly distributed broken wires in 6 rope diameters, or(c) there are 4 randomly distributed broken wires in 30 rope diameters.


15.27 Contact with electric arc

A rigging component or a wire rope that has been contacted by an electric arc must be removed fromservice until certified safe for continued use by a professional engineer.

15.30 Standards

Unless otherwise required by this Regulation, wire rope, alloy steel chain, metal mesh, synthetic fibrerope, synthetic round slings and synthetic fibre web slings must meet the requirements of ASME B30.9-2006 Slings.

15.31 Inspection before use

Slings and attachments must be visually inspected before use on each shift, and defective equipmentmust be immediately removed from service.

15.32 Makeshift fitting prohibition

Makeshift couplers, shorteners, hooks or other load bearing attachments for slings, including thosemade from concrete reinforcing steel, must not be used unless the working load limit has beendetermined and certified by a professional engineer.

15.48 Chain removal criteria

A chain sling must be permanently removed from service or repaired by a qualified person to theoriginal manufacturer's specification or to the specifications of a professional engineer if the chain hasdefects such as stretch or deformation, cracks, nicks or gouges, corrosion pits or burned links.

15.49 Chain wear

(1) A chain sling must be permanently removed from service when the chain link wear is more than themaximum allowed by the manufacturer.(2) If the manufacturer does not specify removal criteria for use in subsection (1), the chain must bepermanently removed from service when the chain size at any point of the link is reduced to the valuesgiven in Table 15-4.

Temperature exposure/operating limits:wire core rope sling 205°C, fibre core wire rope sling 100°C, chain sling 260°C, synthetic fibre webslings 82°C.

Also, select regulations from Section 26, Forestry Operations and Similar Activities:

26.42 Rigging

(6) Rigging must be inspected at regular and frequent intervals by a qualified worker.


26.44 Winches

(1) When properly anchored to a winch, the minimum number of wraps of cable left on a winch drummust be(b) for other types of logging equipment, 3 complete wraps.

26.45 Prohibition of knots

A knot must not be used in any winch line or other rigging, except (a) to effect temporary repair in theevent of line breakage, or (b) for tag lines on grapple log loaders or for hooks on strawline eyes

14. WORKSAFE NEW ZEALAND

Worksafe New Zealand has issued a fact sheet on winch-assisted harvesting which includes applicablesections of Part 6.4 of the New Zealand’s Approved Code of Practice for Safety and Health in ForestOperations plus additional guidance (Worksafe New Zealand, 2016). Part 6.4 of the Code containsrules for winch assist operations. In regard to wire rope the following is relevant.

6.4.2 The tension on the wire rope shall be restricted to 33 percent of its breaking load at all times.

AS 2759 – Steel Wire Rope, Safe use, Operation & Maintenance should also be considered whenusing wire rope.

AS/NZS 1418 – Cranes, Hoists, and Winches clearly defines the specifications required in cranes,hoists, and winches, including safe working load and tension limits.

6.4.3 The maximum operating weight of the mobile plant shall not exceed the rated breaking load of thewire rope. This rule can be reasonably extended to all rigging components. The maximum operatingweight should be the weight when fully loaded.

6.4.4 An emergency back-up system shall be incorporated into the operation to ensure the stability ofthe mobile plant should the winch, wire rope or anchor fail.

6.4.5 All winch-assisted mobile plant operations shall have a documented safe work best practice,including as a minimum… and wire rope inspection and maintenance routines, conducted by competentperson

The guidance section includes additional recommendations:

All mobile plant and winch systems used for steep slope harvesting should have an annual engineeringand mechanical inspection by a competent person

Joining splices should not be used to join broken or damaged winch ropes.

Wire ropes used for winch-assisted harvesting on steep slopes should not be used for log extraction orhauling. They should only ever be used in the winch system.


15. WIRE ROPE STORAGE AND HANDLING

This section includes tips for storing and handling wire rope

Storage

• Store in a clean, ventilated, dry place without exposure to chemical fumes, corrosive agents,acid, or ocean spray. Rope should not contact the ground

• Consider a protective wrap or coat of lubricant to protect the outer layer• Rotated the reel occasionally to distribute the lubricant• Keep away from heat, such as steam or hot water that can thin the lubricant

Installation

• Position the reel correctly so the winding process will spool correctly i.e. over-wind to overwind,or under-wind to under-wind (Figure 17)

• Ensure no twists are introduced into the rope

Figure 17. Correct and incorrect spooling(Herzog Forsttechnik AG, 2013)


Possible causes of improper line spooling include:

• Twist in line or other damage.• Wrong lay of line.• Wire rope wound loose on drum.• Line spooled on too loose.- Always spool line onto drum with a moderate amount of resistive

load.• Line diameter (actual, measured) larger or more than 3% smaller, than pitch of drum

grooves.• Drum damage.• Line rubbing on fairlead components other than sheaves and rollers (T-Mar Industries Ltd.,

2015)Handling

• A swivel should never be used with a flattened strand or lang lay rope• The life of an rope can be extended by “upending” it or switching it end for end by

distributing wear more evenly and using the section of rope that is usually stored on thedrum during use

Lubrication

Recommendations in the literature about lubrication may prove confusing for winch assist operators. Allmanuals emphasize the importance of good lubrication to reduce bending fatigue and increase life.However, there is also advice to never lubricate a rope that normally contacts the soil during operationsas the lubricant will pick up fine particles which will cause abrasion to the rope and sheaves. The bestapproach would be to always rig and operate the systems so there is no soil contact and lubricate therope as recommended by the manufacturer. If it is necessary to operate with soil contact, clean therope regularly and do not apply additional lubrication; replace the rope sooner. A ‘dry” rope unaffectedby corrosion but subject to bend fatigue is likely to achieve only 30% of that normally attained by a‘lubricated’ rope (Herzog Forsttechnik AG, 2013).

Wire rope must be cleaned before applying lubrication. A wire brush can be used to help remove dirt.Lubricants can be applied in several ways: brush, cloth, spray, drip feed, or high pressure lubricatingmachines. Consult your rope manufacturer to determine the method and lubricant that is best for yourrope as some may not be compatible with the rope’s original lubricant.

Removal of broken wires

Broken wires should not be cut off. Instead, the ends should be held with pliers and bend back andforth until the wire breaks in the valley between the strands. If left unattended broken wires maydamage adjacent wires and sheaves.

How to maximize your rope’s life

ISO 4309:2010(E) Chapter 4.4: For optimal performance, the effective sheave groove diameter shouldbe larger than the nominal rope diameter by about 5 % to 10 %, and ideally, at least 1 % greater thanthe actual diameter of the new rope (Herzog Forsttechnik AG, 2013).


15. REFERENCES CITED

Bridon, 2009. Steel Rope Technical Information. [Online]Available at: http://www.bridon.com/china/x/downloads/steel_technical.pdf[Accessed 15 March 2017].

Bridon, n.d. Rope Selection Criteria. [Online]Available at: http://www.bridon.com/us/technical-information/rope-selection-criteria.pdf[Accessed 15 March 2017].

Cafe, T., n.d. Physical Constants for Investigators. [Online]Available at: http://www.tcforensic.com.au/docs/article10.html[Accessed 15 March 2017].

Canadian Centre for Occupational Health and Safety, 2013. Materials Handling - Hoist Wire Rope :OSH Answers. [Online]Available at: http://www.ccohs.ca/oshanswers/safety_haz/materials_handling/hoist.html[Accessed 13 May 2016].

Certex, n.d. Temperature Effect on Working Load Limit. [Online]Available at: http://www.certex.se/en/products/technical-description/steel-wire-ropes/technical-description-slings/temperature-affect-on-working-load-limit__22338[Accessed 15 March 2017].

Convergence Training, n.d. Wire Rope Safety and Operation. [Online]Available at: https://www.convergencetraining.com/wire-rope-safety-and-operation.html[Accessed 15 March 2017].

Dean, M., 2016. Whistler/Blackcomb Fleet Manager [Interview] (22 May 2016).

Fatzer, n.d. [Online]Available at: http://www.fatzer.com/[Accessed 15 March 2017].

Harrill, H., 2016. Steep Terrain and Cable-Assist Workshop. Nanaimo, B.C.: s.n.

Herzog Forsttechnik AG, 2013. HERZOG ALPINE Synchrowinch Universal: Operator's manual, s.l.:s.n.

Infrastructure Health and Safety Association, 2012. Hoisting and Rigging Safety Manual.. [Online]Available at: https://www.ihsa.ca/PDFs/Products/Id/M035.pdf[Accessed 15 March 2017].

ISO, 2010. International Standard 4309 - Cranes — Wire ropes — Care and maintenance, inspectionand discard. [Online]Available at: http://www.wiretech.no/wp-content/uploads/2016/11/ISO_4309_2010.pdf[Accessed 25 May 2017].


Macey, T., 1998. Development of a remote control electromagnetic wire rope inspection systemprotoype, Technical Note TR-276, Vancouver, BC: FERIC.

Muirhead, D., 2017. President, Inter-Mtn Testing [Interview] (29 May 2017).

NDT Technologies, 2012. Electromagnetic Wire Rope Inspection System. Specification Sheet. [Online]Available at: http://www.ndttech.com/docs/Specification_USB_12-29-2012.pdf[Accessed 15 March 2017].

Rheinberger, S. J., 1992. Selecting Wire Rope Design Factors In Cable Yarding. A Review andProposal., s.l.: s.n.

Shah, K. P., n.d. The Hand Book on Mechanical Maintenance. [Online]Available at: http://practicalmaintenance.net/?p=551[Accessed 15 March 2017].

Shingley, J. E. & Mitchell, L. D., 1983. Mechanical Engineering Design. New York: McGraw Hill.

Suwan, K., n.d. Wire Rope Safety Information. [Online]Available at: http://www.numberonesafety.com/Safetytip-Wirecoresling.html[Accessed 15 March 2017].

T-Mar Industries Ltd., 2015. LC150 Steep Slope Traction Assist Machine Operation and MaintenanceManual, s.l.: s.n.

Union Wire Rope, 2009. Tech Report No. 107: Wire Rope Inspection. [Online]Available at: http://www.unionrope.com/Resource_/TechnicalReference/2476/Tech%20Report107-2014.pdf[Accessed 15 March 2017].

Unirope Ltd., n.d. Number of Broken Wire Discard Tables. [Online]Available at: http://unirope.com/number-broken-wire-discard-tables/[Accessed 15 March 2017].

Unirope Ltd., n.d. Relative Service Life, Loss of Strength over Sheaves and Pins, Why Multi-strandWire Rope?. [Online]Available at: http://unirope.com/relative-service-life-loss-strength-pins-why-multistrand-ropes/[Accessed 15 March 2017].

US Department of Agriculture, 1978. Logging Systems Guide, Series No. R10-21. April 1980 ed.Juneau: USDA.

Verreet, D.-I. R., 2002. A short history of wire rope. [Online]Available at: http://www.dep-engineering.fr/pdf/Rope%20history%20by%20RV-court.pdf[Accessed 15 March 2016].

Verreet, R., n.d.. Casar – Special Wire Ropes, Steel Wire Ropes for Cranes, Problems and Solutions.[Online]


Available at: http://www.ropetechnology.com/bro_engl/casar_steel_wire_ropes.pdf[Accessed 26 May 2017].

Verreet, R. & Ridge, I., 2006a. A forensic approach to wire rope defects - Cranes today. [Online]Available at: http://www.cranestodaymagazine.com/features/a-forensic-approach-to-wire-rope-defects/[Accessed 13 May 2016].

Verreet, R. & Ridge, I., 2006b. More causes of wire rope damage - Cranes today. [Online]Available at: http://www.cranestodaymagazine.com/features/more-causes-of-wire-rope-damage/[Accessed 13 May 2016].

Verreet, R. & Ridge, I., 2006c. Tying up the loose ends - Cranes Today. [Online]Available at: http://www.cranestodaymagazine.com/features/tying-up-the-loose-ends/[Accessed 13 May 2016].

Visser, R., 2016. Steep Terrain and Cable-Assist Workshop.. Nanaimo, B.C.: s.n.

Wire Rope Technical Board, 2005. Wire Rope Users Manual. Alexandria: Wire Rope Technical Board.

Wirerope Works Inc., n.d. Technical Bulletin No. 9: Fatigue. [Online]Available at: http://www.wwwrope.com/product_pdfs/el_tb_09.pdf[Accessed 15 March 2017].

Workplace Safety North, 2011. Principles of Rigging, Hoisting and Towing in Logging Operations. NorthBay: Workplace Safety North.

Worksafe New Zealand, 2016. Winch-Assisted Harvesting on Steep Slopes: Fact Sheet. [Online]Available at: http://forestry.worksafe.govt.nz/assets/resources/WSNZ-2266-Winch-Harvesting-Steep-Slopes-FS-v4-0-FA1-LR.pdf[Accessed 15 March 2017].

WorkSafeBC, 2006. Cable Yarding Systems Handbook. [Online]Available at: https://www.worksafebc.com/en/resources/health-safety/books-guides/cable-yarding-systems-handbook?lang=en[Accessed 24 May 2017].

WorkSafeBC, n.d. Occupational Health and Safety Regulations: Rigging. [Online]Available at: https://www.worksafebc.com/en/law-policy/occupational-health-safety/searchable-ohs-regulation/ohs-regulation/part-15-rigging[Accessed 15 March 2017].


16. APPENDIX: WIRE ROPE SPECIFICATIONS AND DISCARDINFORMATION

Typical wire rope specifications (WorkSafeBC, 2006)

Broken wire discard criteria (Unirope Ltd., n.d.)

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Wire Rope Integrity for Winch-Assisted Forestry Equipment

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