Current through September 2, 2024
01.
General Characteristics. Wire rope comes in many grades and dimensions, and every rope has its own characteristics with regard to strength and resistance to crushing and fatigue. A larger rope will outlast a smaller rope of the same materials and construction, used in the same conditions, because wear occurs over a larger surface. Similarly, a stronger rope will outlast a weaker rope, because it performs at a lower percentage of its breaking strength, with reduced stress.
02.
Wire Rope Terms. Common grades of wire rope include extra improved plow steel (EIPS) and swaged powerflex, among others. The following terms are commonly used for wire rope:
a. Abrasion Resistance. Ability of outer wires to resist wear. Abrasion resistance is greater with larger wires.
b. Core. The foundation of a wire rope which is made of materials that will provide support for the strands under normal bending and loading conditions. A fiber core (FC) can be natural or synthetic. If the core is steel, it can be a wire strand core (WSC) or an independent wire rope core (IWRC).
c. Crushing Resistance. Ability of the rope to resist being deformed. A rope with an independent wire core is more resistant to crushing than one with a fiber core.
d. Die-form Line. Made from strands that are first compacted by drawing them through a drawing die to reduce their diameter. The finished rope is then swaged or further compressed.
e. Fatigue Resistance. Ability of the rope to withstand repeated bending without failure (the ease of bending a rope in an arc is called its "bendability"). Fatigue resistance is greater with more wires.
f. Strength. Referred to as breaking strength, usually measured as a force in pounds or tons. The breaking strength is not the same as the load limit, which is calculated as a fraction of the breaking strength to ensure safety.
g. Swaged Line. Manufactured by running a nominal-sized line through a drawing die to flatten the outer crown and thus reduce the rope diameter. This compacted rope allows for increased drum capacity and increased line strength.
03.
Typical Wire Rope Specifications. The table below lists a few examples of wire-rope breaking strengths.
|
TABLE 454.03 - Typical Wire Rope Specifications |
|
6x26 Improved Plow Steel |
6x26 Swaged |
Swaged Compact-Strand |
|
Diameter (inches) |
Weight (lbs/ft) |
Breaking Strength (tons) |
Weight (lbs/ft) |
Breaking Strength (tons) |
Weight (lbs/ft) |
Breaking Strength (tons) |
|
1/2 |
0.46 |
11.5 |
0.6 |
15.2 |
0.63 |
18.6 |
|
9/16 |
0.59 |
14.5 |
0.75 |
19 |
0.78 |
23.7 |
|
5/8 |
0.72 |
17.9 |
0.93 |
23.6 |
1.01 |
28.5 |
|
11/16 | | |
1.10 |
28.8 |
1.18 |
35.3 |
|
3/4 |
1.04 |
25.6 |
1.37 |
34.6 |
1.41 |
42.2 |
|
13/16 | | |
1.56 |
39.6 |
1.63 |
49.3 |
|
7/8 |
1.42 |
34.6 |
1.83 |
46.5 |
1.91 |
56.0 |
|
15/16 | | |
1.95 |
53.3 |
2.20 |
66.1 |
|
1 |
1.85 |
44.9 |
2.42 |
60.6 |
2.53 |
73.7 |
|
1-1/8 |
2.34 |
56.5 |
2.93 |
75.1 |
2.97 |
92.9 |
|
1-1/4 |
2.89 |
69.3 |
3.52 |
92.8 |
3.83 |
112.1 |
|
1-3/8 |
3.5 |
83.5 |
4.28 |
108.2 |
4.62 |
128.6 |
Source: Cable Yarding Systems Handbook. 2006. Worksafe BC. Table lists typical breaking strengths. See manufacturer's specifications for specific lines.
04.
Synthetic Rope. High-tensile strength synthetic lines are considerably lighter than standard wire rope; however, some lines are dimensionally as strong as standard wire rope. Accordingly, high-tensile strength synthetic lines are permitted to be used in appropriate logging applications, including as substitutes for brush straps, tree straps, tail and intermediate support guylines, guyline extensions, skyline extensions, and haywire. Manufacturers' standards and recommendations for determining usable life or criteria for retirement of such lines shall be followed. Personnel shall examine the lines for broken or abraded strands, discoloration, inconsistent diameter, glossy or glazed areas caused by compression and heat, and other inconsistencies. Rope life is affected by load history, bending, abrasion, and chemical exposure. Most petroleum products do not affect synthetic ropes.
05.
Inspection and Care.
a. Wire rope shall be inspected daily by a qualified individual and repaired or taken out of service when there is evidence of any of the following conditions:
i. Twelve and five tenths percent (12.5%) of the wires are broken within a distance of one (1) lay.
ii. Evidence of chafing, sawing, crushing, kinking, crystallization, bird-caging, corrosion, heat damage, or other damage that has weakened the rope structure.
b. Qualified personnel shall closely inspect those points subject to the most wear, including the knob ends of lines, eye splices, and those sections of line that most often run through blocks or carriages. If there is doubt about the integrity of the line, it is far safer to replace a suspect line, or cut out and resplice a defective area, than risk a failure during operation. Evaluation of the load-bearing yarder lines shall be stringent. A qualified person shall also inspect all other lines used on site and remove any that are unsafe.
06.
Additional Precautions. The following precautions shall also be observed:
a. Ensure the working load limit for any line is adequate for the intended use.
b. The manufacturer's specifications with regard to assigned breaking strength shall be followed. Such specifications as determined by engineering test results should factor the grade of the wire, number of strands, number of wires per strand, filler wire construction, lay pattern of the wires, and the diameter of the line.
07.
Safety Factor. Operators shall follow the manufacturer's specifications in determining load limits. The working load limit is a fraction of a line's breaking strength - a factor of three (3), or one-third (1/3) the breaking strength, is commonly used as a safety factor for running and standing lines, when workers are not exposed to breaking lines or loads passing overhead. A safety factor of three (3) is commonly used to determine the working load limit for a standing or running line. A standard six (6) x twenty-six (26) IWRC wire rope with a diameter of one (1) inch has a breaking strength of approximately forty-five (45) tons - divide by three (3) - equals fifteen (15) tons working load limit.
08.
Wire Labeling.
a. The elements of a typical wire rope are labeled, for example, six (6) x twenty-five (25) FW PRF RL EIPS IWRC. The label indicates a six (6)-strand rope with twenty-five (25) wires per strand (six (6) x twenty-five (25)), filler-wire construction (FW), strands pre-formed in a helical pattern (PRF), laid in a right-hand lay pattern (RL), using an extra-improved plow steel (EIPS) grade of wire, and strands laid around an independent wire rope core (IWRC). See figure 013.08-A for proper labeling of wire rope.
FIGURE 454.08.a.
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b. Out of Service Standard Example. A six (6) x twenty-five (25) IWRC wire rope = six (6) strands in one (1) lay with twenty-five (25) wires per strand = one hundred fifty (150) wires. The rope must be taken out of service when twelve and five tenths percent (12.5%), or one-eighth (1/8), of the wires are broken within the distance of one (1) lay = one hundred fifty (150) divided by eight (8) = eighteen and seventy-five one hundredths (18.75), or nineteen (19) broken wires.
09.
Wire Line Life. Table 454.09 provides the allowable life of a line in million board feet in accordance with line size and use. Figure 454.09.a. illustrates both the correct and incorrect manner in which to measure line size (diameter).
|
TABLE 454.09
LINE LIFE BY WOOD HAULED |
|
System |
Use |
Line Size (inches) |
Line Life (million board feet) |
|
Standing Sky-line |
Skyline |
1-3/4 |
20-25 |
|
1-1/2 |
15-25 |
|
1-3/8 |
8-15 |
|
Mainline |
1 to 1-1/8 |
15-20 |
|
1 |
10-15 |
|
Haulback |
3/4 to 7/8 |
8-12 |
|
Live Skyline |
Skyline |
1-1/2 |
10-20 |
|
1-3/8 |
8-15 |
|
1 |
6-10 |
|
Mainline |
1 |
10-15 |
|
3/4 |
8-12 |
|
5/8 |
8 |
|
Haulback |
3/4 to 7/8 |
8-12 |
|
1/2 |
6-10 |
|
Dropline |
7/16 |
5-8 |
|
High Lead |
Mainline |
1-3/8 |
8-15 |
|
1-1/8 |
6-12 |
Source: Willamette Logging Specialist's Reference by Keith L McGonagill. 1976. Portland, OR: Willamette National Forest. Calculations of line life refer to EIPS 6x21 wire rope for the skyline, and EIPS 6x26 for other lines. Figures will be different for other classes of wire rope.
FIGURE 454.09.a.
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10.
Dynamic Loads. Operators shall consider high dynamic loads when calculating safe working limits of wire ropes. Wire ropes are often subjected to high dynamic loads, which greatly multiply the force on a line and may exceed the safe working limit. Even a split second of time over the limit can lead to premature failure of a line. Typical dynamic loads occur when a turn hits a stump, a turn comes down off of the back hillside to full suspension, or when excessive force is applied to pulling a turnout of its bed. A high dynamic load or a sudden shock load that exceeds the working limit may not result in immediate failure, but rope strands may stretch and weaken, and may fail at a later time.
11.
Other Common Wire Rope Considerations.
a. Wire Rope Stretching and Line Diameter. A stretched wire rope has a reduced diameter. Operators shall check for stretched lines by measuring the diameter, particularly on older lines and any line used in stressful situations.
b. Older Wire Rope. Standing lines and guylines are often kept in service for multiple years (four (4) to five (5), and as long as ten (10) years in some instances) without exhibiting any obvious signs of excessive wear other than rust. Operators shall check date stamps of wire rope and evaluate line life. Operators shall also inspect the core of older lines periodically for a fractured or dry core, which could indicate other deficiencies such as broken wires, excessive wear, or line deformation.
c. Hard Use. The life of a wire rope is also affected by hard use. Line life can be measured by the volume of wood hauled (see Table 459.09). Line life is reduced when a line exceeds its elastic limits, is heavily shocked, or rubbed against rocks or other lines. As a line wears, the safe working load limit shall be lower and the payload adjusted appropriately.
d. Wire Rope endurance and elastic limits. Working within the endurance and elastic limits of lines can help preserve line life. The following principles shall be observed when evaluating the integrity and safe use of wire rope:
i. The "endurance limit" for all lines is fifty percent (50%) of the breaking strength. If wire rope tensioning regularly exceeds the endurance limit, the life of the line is reduced through fatigue.
ii. The "elastic limit" for all lines is sixty to sixty-five percent (60-65%) of the breaking strength. When a wire rope is loaded to its normal safe working limit, the line stretches, but then returns to its original size when the load is released. If a load increases past the elastic limit through prolonged exertion or repeated stress, the line will stretch and stay stretched, resulting in a permanent reduction in the breaking strength.
e. Lubrication and Abrasion. Wire rope is lubricated in the factory to reduce internal friction and corrosion, and prolong the life of the rope. Heat from friction causes the internal lubricant to deteriorate. Friction occurs when the rope stretches under load, particularly in places where it bends around sheaves or other objects. An improperly lubricated line can pick up particles of dirt and sand that will increase abrasion. Accordingly, operators shall:
i. Check for and ensure the proper lubrication of all lines and wire rope, following the manufacturer's instructions. Commercial wire rope lubricants are available.
ii. Carefully inspect lines for faults in areas where dust and sand may collect.
iii. Store all wire rope and lines off the ground.
12.
Line Connections.
a. Inspection. Operators shall regularly inspect shackles, hooks, splices, and other connecting equipment for damage and wear, as well as ensure the connectors are the correct type and size for the line and intended use.
b. Wire Splicing. Splices are used to form an eye at the end of a line, extend the length of a line, or repair a broken or damaged line. The splicing of wire rope requires special skill and shall only be performed under the supervision of a competent person with using the proper tools. Reference materials are available with detailed instructions for numerous types of splices. Individuals splicing wire shall always wear appropriate eye protection while splicing or assisting with a splicing procedure.
c. The logger's eye splice and three (3)-pressed eye are the most common methods to form an eye for use as a skyline terminal. See Figure 454.12.c. The spliced eye is approximately eighty percent (80%) efficient. A three (3)-pressed eye can reach ninety percent (90%) line strength. The pressed eye is typically performed at the rigging shop. Spliced eyes may be placed in the field, but may require additional time to install.
FIGURE 454.12.C.
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d. When Flemish (Farmers, Rolled) eye splices are used on load-bearing lines, the strand ends must be secured by:
i. Hand tucking each strand three (3) times; or
ii. Applying a compression (pressed-eye) fitting.
e. Guyline Care. Guylines are a vital link in holding up a tower. Guyline extensions shall not be excessively moved around by dragging on the ground, or left on the ground for long periods of time as they will deteriorate faster.
f. Guyline extensions must be connected by:
i. A bell shackle using a safety pin to connect spliced eyes or pressed eyes; or
ii. Poured nubbins (buttons) and a double-ended hook.
g. Line Deformity. A line may deform where it loops around a shackle or pin, producing weakness that may result in line failure. A thimble in the loop protects the line. Thimbles may be used on standing lines, but not on running lines. Examples of the appearance of deformed lines and the use of thimbles in shackles are illustrated in Figure 454.12.g.
FIGURE 454.12.g.
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13.
Shackles and Hooks.
a. Hooks. Hooks shall be inspected to ensure that they have not sprung open. Ensure that shackles are positioned correctly to bear the load. Haywire swivels shall be inspected frequently, due to their susceptibility to wear rapidly.
b. Shackle Safety. Proper bells or shackles shall be used to connect the guylines to the stumps, and the guyline lead blocks to the ring at the top of the tower. Connections shall have at least one and a half (1-1/2) times the strength of the guyline. The pins of the shackles must be secured to protect against dislodgement, and a nut and cotter key, or a nut and molly may be used for that purpose. The use of loops or mollies to attach guylines is prohibited. Examples of the appearance of some shackle equipment is illustrated in Figure 454.13.b.
FIGURE 454.13.b.
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c. The following practices shall be observed in order to ensure the safe use of shackles:
i. A shackle must have a rated breaking strength greater than the rated breaking strength of the lines attached to it, and the manufacturer's rated strengths to determine oversized requirements shall be used. Accepted industry standards shall be utilized and adhered to when determining the correct shackle size based on the type and nature of the logging operation being performed. Examples of the appearance of some shackle equipment for the purposes of proper selection is illustrated in Figure 454.13.c.i
ii. Shackles with pins, and securing nuts with mollies or a cotter key shall be used on standing or overhead rigging.
iii. Screw shackle pins shall not be used in any standing or overhead rigging.
iv. Screw shackle pins, where allowed to be used, shall be tightened securely.
v. Shackle pin mollies shall be rolled sufficiently and fit the pin hole fully. Mollies shall be tucked a minimum of three (3) times.
vi. The shackle shall always be placed with the pin nearest to the yarder, so that in the event the shackle fails the least amount of hardware may be thrown at the yarder.
vii. Replace shackles that are bent, broken, or show excess wear on the inner surfaces. Examples of the appearance of some damaged or non-conforming shackles are illustrated in Figure 454.13.c.vii.
FIGURE 454.13.c.vii.
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viii. Sleeve shackles or choker bells must be used when choked lines are permitted.
FIGURE 454.13.c.i.
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14.
Knobs, Ferrules, and Eyes.
a. Poured nubbins and a double-end hook are acceptable connectors in place of shackles in some instances. The use of quick nubbins (wedge buttons) as guylines and skyline end fittings is prohibited unless attaching guy lines to guy line drums. Operators shall follow the manufacturer's recommendations when attaching sockets and similar end fastenings.
b. Poured nubbins achieve ninety-nine percent (99%) of line strength and may be used. Quick nubbins only achieve a maximum of sixty-five percent (65%) under ideal conditions, and accordingly operators shall consider whether they are appropriate for safe use in any given application. Pressed ferrule are not certifiable for strength, and shall not be used. Examples of the appearance of some knob, ferrule, and nubbin equipment are illustrated in Figure 454.14.
c. Operators shall inspect knobs, ferrules, and eyes at cable ends for loose or broken wires, and corroded, damaged, or improperly applied end connections. Poured nubbins shall be date stamped.
FIGURE 454.14
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15.
Brush Blocks. Brush blocks shall be thoroughly inspected for cracks, wear, or deterioration.
Operators shall closely examine the areas subject to the most wear, including bearings, sheave, frame, yoke, and pins. Defective parts shall be replaced immediately. Blocks shall be greased every time before each use.
FIGURE 454.15
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16.
Chains and Straps. Chains or straps shall always be sized and used correctly for the intended purpose. Determining which size to use may depend on various factors. Oversized trailer lift straps, for example, shall have a breaking strength equal to five (5) times the load to be lifted. Towing chains shall have a tensile strength equivalent to the gross weight of the towed vehicle. The manufacturer's specifications or other appropriate reference materials shall always be consulted to ensure the right chain or strap is used for a task.
a. Operators shall periodically inspect chains for damaged, worn, or stretched links. Chains with more than ten percent (10%) wear at the bearing surface shall be replaced. Operators shall periodically inspect straps, and examine them for broken wires or wear. Examples of the appearance of damaged and safe chains are illustrated in Figure 454.16.a.
FIGURE 454.16.a.
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Effective March 31, 2022
