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    Samson Rope Information Sheet

    Samson Rope Information Sheet

    ROPE SELECTION, USE AND INSPECTION

    Rope Selection, Use and Inspection

    The use of rope for any purpose results in friction, bending and tension. All rope, hardware, sheaves rollers, capstans, cleats, as well as knots are, in varying degrees, damaging to ropes. It’s important to understand that rope is a moving, working, strength member and even under the most ideal conditions will lose strength due to use in any application. Maximizing the safety of rope performance is directly related to how strength loss is managed and making sure ropes are retired from service before a dangerous situation is created. Ropes are serious working tools and used properly will give consistent and reliable service. The cost of rope replacement is extremely small when compared to the physical damage or personnel injury that can result from using a worn out rope.


    There are basically three steps to consider in providing the longest possible service life for ropes, the safest conditions and long range economy: Selection, Usage and Inspection.

     

    Rope Selection

    Selecting a rope involves evaluating a combination of factors. Some of these factors are straight forward, like comparing rope specifications. Others are less qualitative, like color preference or how a rope feels while handling. Cutting corners, reducing design factors, sizes or strengths on an initial purchase creates unnecessary replacements, potentially dangerous conditions and increased long term costs. Fiber and construction being equal, a larger rope will outlast a smaller rope, because of greater surface wear distribution. By the same token, a stronger rope will outlast a weaker one, because it will be used at a lower percentage of its break strength and corresponding Work Load Limit with less chance of overstressing. The following factors should be considered in your rope selection: Strength, Elongation, Firmness, Construction and Abrasion.

     

    Strength

    When given a choice between ropes, select the strongest of any given size. A load of 200 pounds represents 2% of the strength of a rope with a 10,000 Lbs. breaking strength. The same load represents 4% of the strength of a rope that has a 5,000 Lbs. breaking strength. The weaker rope will work harder and as a result will have to be retired sooner. Braided ropes are stronger than twisted ropes that are the same size and fiber type.


    Please note that the listed break strengths are average break strengths and do not consider conditions such as sustained loads or shock loading. Listed break strengths are attained under laboratory conditions. Remember also that break strength is not the same as the Work Load Limit.

     

    Elongation

    It is well accepted that ropes with lower elongation under load will give you better control. However, ropes with lower elongation that are shock loaded, like a lowering line, can fail without warning even though the rope appears to be in good shape. Low elongating ropes should be selected with the highest possible strength. Both twisted ropes and braided ropes are suitable for rigging. Size for size, braided rope has higher strength and lower stretch than a twisted rope of similar fiber. See page 390 for additional information on rope elongation.

     

    Firmness

    Select ropes that are firm and hold their shape during use. Soft or mushy ropes will snag easily and abrade quickly causing accelerated strength loss.

     

    Construction and Abrasion

    Rope construction plays an important role in resistance to normal wear and abrasion. Braided ropes have a basically round, smooth construction that tends to flatten out somewhat over the bearing surface. Flattening distributes wear over a much greater area, as opposed to the crowns of a three strand or to a lesser degree, an eight strand rope.


    All rope will be severely damaged if subjected to rough surfaces or damaging edges. All rope must be protected against damaging or abrasive surfaces. Wire rope will score and gouge chocks and bitts creating cutting edges that can damage synthetic ropes. Chocks, bitts, drums and other surfaces must be kept in good condition and free of burrs and rust. Weld beads on repaired capstans, fairleads, etc., are equally damaging, unless dressed down smoothly. Pulleys must be free to rotate and should be of proper size to avoid
    excessive wear.

     

    Rope Inspection

    Avoid using a rope that shows signs of aging and wear. If in doubt, do not use the rope. Damaged rope must be destroyed to prevent any future use. No visual inspection can be guaranteed to accurately and precisely determine the residual strength of the rope. When fibers show wear in any area, the damaged area must be removed and the rope should be re-spliced or replaced. Check regularly for frayed or broken strands. Pulled strands should be rethreaded into the rope if possible. A pulled strand can snag on a foreign object during usage. Both outer and inner rope fibers may contribute to the strength of the rope. When either is worn the rope is naturally weakened. Open the strand of the rope and inspect for powdered fiber, which is one sign of internal wear. A heavily used rope will often become compacted or hard, which indicates reduced strength. The rope should be discarded and made unusable if this condition is detected. See pages 395 and 396 for additional inspection information.

     

    New Rope Tensile Strength

    New rope tensile strength is based upon tests of new and unused spliced rope of standard construction in accordance with Samson testing methods, which conform to Cordage Institute, ASTM and OCIMF test procedures. It can be expected that strengths will decrease as soon as a rope is put into use. Because of the wide range of rope use, changes in rope conditions, exposure to the many factors affecting rope behavior and the possibility of risk to life and property, it is impossible to cover all aspects of proper rope applications or to make generalized statements as to Work Load Limits.

     

    Work Load Limits

    Work Load Limits are the load that a rope in good condition with appropriate splices in non-critical applications is subjected to during normal activity. They are normally expressed as a percentage of new rope strength and should not exceed 20% of the stated break strength. Thus, your maximum Work Load Limit would be 1/5 or 20% of the stated break strength.


    A point to remember is that a rope may be severely overloaded or shock loaded in use without breaking. Damage and strength loss may have occurred without any visible indication. The next time the rope is used under normal Work Loads and conditions, the acquired weakness can cause it to break.

    Normal Work Load Limits do not cover dynamic conditions such as shock loads or sustained loads, nor do they apply where life, limb or property are involved. In these cases a stronger rope must be used and/or a higher design factor applied.

     

    Normal Work Load Limits

    Normal Work Load Limits are not applicable when rope is subjected to dynamic loading. Whenever a load is picked up, stopped, moved or swung there is increased force due to dynamic loading. The more rapidly or suddenly such actions occur, the greater the increase in the dynamic loading. In extreme cases, the force put on the rope may be two, three or many more times the normal Work Load involved. Examples of dynamic loading would be: towing applications, picking up a load on a slack line or using a rope to stop a falling object. Dynamic loading affects low elongation ropes like polyester to a greater degree than higher elongation, nylon ropes. Dynamic loading is also magnified on shorter length ropes when compared to longer rope lengths. Therefore, in all such applications, normal Work Load Limits do not apply.

     

    Work Load Limits

    Construction Type

    Work Load Limit
    (% of Break Strength)

    3 Strand

    20%

    8 Strand

    20%

    12 Strand

    20%

    IMPORTANT NOTE: Many industries are subject to state and federal regulations for Work Load Limits that supersede those of the manufacturer. It is the responsibility of the user to be aware of and adhere to those laws and regulations.

     

    Shock Loads

    Work Load Limits as described do not apply when ropes have been subjected to shock loading. Whenever a load is picked up, stopped, moved or swung, there is an increased force due to dynamic loading. The more rapidly or suddenly such actions occur, the greater this increase in force will be. The load must be handled slowly and smoothly to minimize dynamic effects. In extreme cases, the force put on the rope may be two, three or even more times the normal Work Load involved. Examples of shock loading are picking up a tow on a slack line or using a rope to stop a falling object. Therefore, in all applications such as towing lines, life lines, safety lines, climbing ropes, etc., design factors must reflect the added risks involved. Users should be aware that dynamic effects are greater on a low elongation rope such as manila than on a high-elongation rope such as nylon and greater on a shorter rope than on a longer one.


    The shock load that occurs on a winch line when a 5,000 Lbs. object is lifted vertically with a sudden jerk may translate the 5,000 Lbs. of weight into 30,000 Lbs. of dynamic force, which could cause the line to break. Where shock loads, sustained loads or where life, limb or valuable property is involved, it is recommended that a much higher design factor than 5 be used.

    Remember, shock loads are simply a sudden change in tension, from a state of relaxation or low load to one of high load. The further an object falls, the greater the impact. Synthetic fibers have a memory and retain the effects of being overloaded or shock loaded. Ropes that have been shock loaded can fail at a later time, when used within Work Load Limits.

     

    Stength Degradation from UltraViolet Light

    Prolonged exposure of synthetic ropes to ultraviolet (UV) degradation from any source causes varying degrees of strength loss.
    Polyester fibers are least affected by UV exposure, while Nylon is more susceptible. With both nylon or polyester, the degree of susceptibility to UV damage is dependent on the type of fiber, length of exposure and the protection afforded by various treatments and inhibitors, i.e., Samthane coating.

    Polyolefin and PRO fibers are severely affected by ultraviolet exposure, especially in their natural, undyed, non-treated and/or uncovered states.

    Danger to Personnel

    Persons should be warned against the serious danger of standing in line or under a rope while the rope is under tension. Should the rope part, it may recoil with considerable force. In all cases where any such risk is present or where there is any question about the load involved or the condition of use, the Work Load Limit should be substantially reduced and the rope properly inspected before every use..

     

    Bending Radius

    Any sharp bend in a rope under load decreases its strength substantially and may cause premature damage and failure. In sizing the radius of bitts, fairleads and chocks the following guidelines are offered:
    Where a rope bends more than 10 degrees around bitts, chocks or across any surface, the diameter of the contact surface should not be less than 3 times the rope diameter. A ratio of 4 to 1 (or larger) would be better because the rope durability increases as the diameter of the surface over which it is worked increases.


    The ratio of the length of an eye to the diameter of the object over which it is being placed should be a minimum of 3 to 1 and preferably 5 to 1. In other words, if you have a 2 Ft. diameter bollard, the eye length should be a minimum of 6 Ft. and preferably 10 Ft. By using this ratio, the base of the eye will be spared from tearing or parting. Thimbles are normally designed for use at a 3 to 1 ratio.

     

     

    Sheave diameters on rotating sheave blocks should be 10 times the rope diameter for twisted ropes and 8 times the rope diameter for braided ropes. Diameters on fixed pin terminations should be at least 3 times the rope diameter, i.e., the bending radius for 1/2” diameter rope should be 1-1/2 inches.

     

    Knots

    While it is true that a knot reduces rope strength, it is also true that a knot is a convenient way to accomplish rope attachment. The strength loss is a result of the tight bends that occurs in the knot. With some knots, ropes can lose 50% of their strength. It is vital that the reduction in strength by the use of knots be taken into account when selecting rope size and strength for any application. To avoid knot strength reduction, it is recommended that a rope be spliced according to the manufacturer’s instructions.

     

    Rope Storage

    All rope should be stored in a clean and dry location, away from direct sunlight and extreme heat. It should be kept off the floor and
    placed on racks to provide ventilation. Never store rope on concrete or dirt floors and under no circumstance should rope be kept in the same vicinity with acids or alkalis. Some synthetic rope (in particular polypropylene and polyethylene) may be severely weakened by prolonged exposure to ultraviolet light (UV) rays unless specifically stabilized and/or pigmented to increase UV resistance. UV degradation is indicated by discoloration and the presence of splinters and slivers on the surface of the rope.

     

    Avoid Chemical Exposure

    Rope is subject to damage by chemicals. Sulfuric acids and alkalis are to be avoided. Chlorinated hydrocarbons at temperatures in excess of 160 degrees, strong cleaning agents and bleaches are harmful. Consult the manufacturer for specific chemical exposure and recommendations. The user must be aware of any situation where damaging chemicals would directly contact the rope or the rope be exposed to fumes, vapors or mists of damaging chemical agents.

     

    Avoid Overheating

    Heat can seriously affect the strength of synthetic ropes. The temperatures at which 50% strength loss can occur are: polypropylene at 250º F and nylon or polyester at 325º F. When using rope where temperatures exceed these levels (the rope is too hot to hold) consult the manufacturer for recommendations as to the size and type of rope for the proposed situation. When using ropes on a capstan or winch, care should be exercised to avoid surging while the capstan or winch head is rotating. The friction from the slippage causes localized overheating which can melt or fuse synthetic fibers, resulting in severe loss of tensile strength.

     

    Dielectric Properties

    Based on rope industry practices, dielectric property testing is conducted on clean, dry, new rope samples and holds true only under these ideal, laboratory conditions. Dirt, grease, other foreign matter, moisture and humidity will alter the non-conductivity or conductivity of any synthetic material. No rope manufacturer can attest to dielectric properties under actual operating conditions.

     

    Removing Rope from Reel or Coil

    Synthetic fiber ropes are normally shipped on reels for maximum protection during transit. The rope should be removed from the reel by pulling it off the top while the reel is free to rotate. This can be done by passing a pipe through the center of the reel and jacking it up until the reel is free to rotate. Rope should never be taken from a reel lying on its side. If the rope is supplied on a coil, it should always be uncoiled from the inside so that the first turn comes off the bottom in a counter-clockwise direction.


    Rope Storage: Coiling & Flaking

    Great care must be taken in the storage and proper coiling of 3-strand ropes to prevent the natural built in rope twist from developing kinks and hockles. Braided ropes on the other hand have no built in twist and are far more resistant to kinking. Even if kinks develop in braided ropes, they cannot develop further into hockles . Three strand and braided ropes should be coiled in a clockwise direction, or in the direction of the lay of the rope. These ropes should be uncoiled in a counter-clockwise direction to avoid kinks. An alternate and perhaps better method is to flake out the line in a Figure 8. This avoids putting twist in the line in either direction and lessens the risk of kinking.

    The best method for deck stowage of braided rope is a Figure 8, whether placed flat on the deck or vertically around bulkhead or cleats. Braided ropes should not be hand coiled in either direction as this puts twist into the line which may develop into kinks when paying out. Remember, originally there is no twist in braided ropes, so do not produce it by coiling.

     

     

    Fatigue

    Synthetic fibers have a memory. They function similar to metal in that fibers remember and retain the effects of being overloaded and shock loaded. This is an important reason to stress winch line procedures which reduce the danger of shock loading for safety and increased service life. If there is any reason to suspect that a line has been shock loaded beyond the Work Load Limit, the incident should be recorded and trigger line inspection, rotation and/or replacement.

     

    Knots

    It is widely known that knots significantly reduce rope strength and result in reduced Work Load Limits. Please note that all reductions for knots are approximations. Actual results may vary depending upon: rope diameters, constructions, materials, etc. Commonly used knots and their impact on rope strength are depicted for your consideration:

     

    SHEEP BEND
    The sheep bend is used instead of a square knot to tie two lines of different diameters together. Be sure to slide the smaller line down onto the loop. The sheep bend reduces rope strength by 50%.

    BOWLINE
    The bowline will not slip or jam and is easily tied and untied. The bowline reduces rope strength by 40%.

     

     

    COW HITCH
    The cow hitch provides a suitable method of joining two ropes of similar diameters without the use of thimbles or other hardware. The cow hitch will reduce rope strength by approximately 15%.