1. Care in Use
3. Inspection & Retirement
4. Lifetime Factors
Care in Use
Ropes should be stored in a suitable clean, dry place out of direct sunlight and away from extreme temperature. Do not store ropes on dirty floors or drag over rough ground – dirt and grit can work between the fibres and cause abrasion damage. Keep ropes away from chemicals and in cases of long term storage, hose down with fresh water to reduce dirt and salt that can affect the life and efficiency.
3 Strand ropes may become damaged if they are taken from a coil the wrong way. If this happens turn the coil over and withdraw the rope from the centre – the rope should run correctly without kinking
Braided ropes can have excessive twist imparted into them by incorrect handling. Ideally these ropes should be “hanked” in a figure of 8 fashion avoids putting twist in and will ensure free running when deployed.
If supplied on a reel, this must be allowed to rotate freely on a central pin so that the rope may be drawn off from the top layer. Never take the rope from a reel lying on its side unless placed onto a turntable.
Sheaves, pulleys and rollers
When any rope is used around a sheave there will be a reduction in its strength and life. For most non-specialised applications a sheave diameter 8-10 times the rope diameter will suffice, however certain materials such as Aramids may require a sheave size of up to 20 times diameter
The profile of the groove in a sheave should support the entire rope. Normally a semicircle of 10% greater diameter than that of the rope is appropriate. ‘V’ groove sheaves should be avoided since they compress the rope and have points of local friction reducing the life of the rope. Sheaves should be maintained so that they rotate freely in use.
Winches and capstans
When a rope is wound onto a winch it is important that the wraps are neat and tightly wound. This can be achieved by winding the rope on whilst under tension. If the rope is wound on slack then it will be more prone to burying between the turns of the previous layer.
When using ropes on winches or capstans the friction between the rope and the barrel is vitally important since this will determine the amount of slip and the number of turns needed. This friction is dependent on the rope material and construction as well as the surface finish in contact with the rope. Since the rope’s geometry will change depending on load the friction can also change slightly.
The materials used in the construction of synthetic fibre ropes can be affected by exposure to chemicals, often this will reduce the strength of the rope - see physical properties section for more information. Each of the materials is affected differently by different chemicals, if chemical exposure is expected contact Marlow ropes for more details. If a rope has been exposed to a chemical that may have caused damage it should be retired from use. Chemical damage often appears as discoloured or powdery / dusty yarns however the rope can be significantly weakened with no visible effects.
Exposure to elevated temperatures can change the properties of a rope. In some cases these changes can be beneficial e.g. Pre stretching and heat setting. More often the effects of heat will be to reduce the strength and damage the rope. It is important to avoid exposing a rope to localised heat sources or elevated temperatures. This must be ensured both in use and when the rope is stored.
Friction generated heat
When a rope is used on a winch or capstan it is possible to generate enough heat through friction to melt or fuse the fibres of the rope resulting in a reduction in performance. To avoid this care should be taken to avoid excessive slipping or surging. Many ropes are designed specifically to withstand friction generated heat - please contact our technical department for more details.
All the materials used in the construction of synthetic fibre ropes are to a greater or lesser extent effected by exposure to UV radiation. Wherever possible try to limit the exposure of the rope to sunlight. Smaller ropes are effected more than large ropes since they have a larger exposed surface area in proportion to their volume. The effect of UV radiation on a rope is directly linked to the inherent UV properties of the yarn used in design and manufacture - see physical properties section for more information.
All ropes can be damaged if they are exposed to abrasive surfaces or sharp edges. Care should be taken to try and avoid running a rope over any non-moving surface. If the rope is run over sheaves or rollers they should be kept in good order with a smooth surface and they must be free to rotate.
Abrasion can also be caused by the ingress of particles into the rope. Conditions where a rope will come into contact with sand, dirt, grit and other abrasive particles should be avoided. Damage caused by this type of abrasion may not be visible on the outside of a rope yet the strength may be severely reduced.
- Splices: Most Marlow ropes can be spliced, this is normally the preferred method of termination. A good splice using the recommended method should not reduce the strength of a rope by more than 10%.
- Knots: A knot will reduce the strength of the rope, sometimes very significantly. This loss is caused by the tight bends and compression found in any knot. The amount a rope will be weakened will depend on the knot, type of rope and the material from which it is made but can be up to 60%
- Eye Sizes: Wherever possible the angle formed at the throat of a splice when it is loaded should be 30 degrees or less. This means that the length of the eye when flat must be at least 2.7 times the diameter of the object over which the eye is to be used and the distance from the bearing point to the throat when in use should be at least 2.4 times the diameter.
Some materials like Aramids and HMPEs will require a larger eye with an angle at the throat of 15 degrees or less.
Inspection and Retirement
It is important that a rope is regularly inspected to ensure that it is undamaged and is still fit for service. The entire length of rope should be examined. The following are some of the points that should be checked. The degree to which any of the following may be allowed before the rope is retired will be dependant on the assumptions made when the rope and safety factors were determined.
- External abrasion: When a multifilament rope is subjected to abrasion then the outer filaments will quickly become broken and a furry finish will develop. This furry layer will protect the yarns underneath preventing further abrasion. If this condition does not stabilise and continues to develop then there may be excessive abrasion that could lead to significant strength loss.
- Internal Abrasion: The rope should be opened up so that the condition of the internal yarns can be assessed. If they show signs of abrasion then there could be some exposure to abrasive particles or there may be inter yarn abrasion.
- Glazing: If a rope has been subjected to excessive heat then there may be glazed or glossy areas of rope. The glazing is caused when the yarns melt, if this has happened then the nearby yarns will also have been exposed to elevated temperatures and will have been affected. This type of damage is often seen if ropes slip on winch barrels or capstans.
- Discoloration: This could indicate the presence of dirt that may cause internal abrasion or could be an indication of chemical damage. If chemical damage is suspected then the amount that the rope has been weakened is very difficult to asses and the rope should be retired.
- Inconsistencies: If any section of the rope is found to contain lumps, flat areas or thin bits then this could indicate that the rope has been damaged internally. This type of damage is often caused by overloading or shock loads.
No rope will last forever and it is important to ensure that if there are any risks if a rope fails then it should be retired after an appropriate period.
- Tension-Tension Fatigue: Tension fatigue will occur any time a rope is loaded. It is related to the loads that the rope is subjected to. It is possible to improve the ropes resistance to this type of fatigue by applying marine finishes to the yarn. The life of a rope can be improved by using at a lower load. Rope constructions with low ‘construction’ have good resistance to this type of fatigue.
- Bending Fatigue: Bending fatigue occurs any time a rope is flexed. It is important to allow for this if a rope is used on sheaves or rollers. This form of fatigue is related to the load and can still occur at very low tensions. Rope constructions with high ‘construction’ have good resistance to this type of fatigue.
- Compression fatigue: This is a rare form of fatigue that only occurs if a rope or components of a rope go into compression. In this situation ‘kink bands’ can form in the individual filaments reducing their strength. Compression fatigue can be avoided by maintaining the tension in the rope, using a rope with more ‘construction’ and ensuring that any sheaves and rollers are large enough to prevent any component of the rope from going into compression. Most fibres are resilient to compression but care needs to be taken when Aramids are used.
- Creep: Creep is a permanent extension due to molecular slippage, it occurs when a load is held on a rope for a period of time. Most materials will exhibit creep to some degree. Creep rate will increase at higher temperatures or higher loads. The fibres most effected by creep are polypropylene and polyethylene.
- Exposure to Water: The properties of nylon are changed slightly when it becomes wet. The fibre shrinks, the strength is reduced by up to 15% and the extension increases. The other materials used in rope making are largely unaffected by even prolonged exposure to water.