Water Well Journal
Issue link: https://read.dmtmag.com/i/629532
F iber rope and wire rope are widely used across the groundwater industry. Fiber rope is more commonly used in manual hoisting, such as raising up or lowering down tools. Wire rope is commonly used for mechanical hoisting operations. The improper use of fiber rope or wire rope can result in serious incidents involving property damage, injuries, and death. Using the ropes as intended within their safe working load and maintaining them in good condition are critical in preventing rope failures. Both types of rope include a combination of characteristics that give them certain performance traits depending on design, materials, and composition. Wire Rope Construction Wire rope is made of steel wires laid together to form a strand. These strands are laid together to form a rope, usually around a central core of either fiber or wire. The number of strands, number of wires per strand, type of material, and nature of the core depend on the intended pur- pose of the wire rope. Wire rope that has many smaller wires and strands is more flexible than rope with larger-diameter wires and fewer strands. Wire rope used with sheaves and drums should have many strands to be flexible enough to bend around the sheaves and drums. Wire ropes are classified by grouping the strands according to the number of wires per strand. The number of wires and the pattern defines the rope's characteristics. For example, a 6 × 7 rope indicates the rope is comprised of six strands and each individual strand is comprised of seven wires. This particular rope has large wires and is not very flexible but has good abrasion-resistant qualities. Whereas, a 6 × 19 rope has 19 wires per strand and thus is more flexible. The more wires in a strand, the more flexible the wire rope. Likewise, the more strands in the rope, the more flexible the rope. However, the more strands in a rope and more wires in a strand, the less abrasion resistant. Other important requirements to consider when selecting a wire rope are the breaking strength and "safe working load." These values can be found with the use of a chart. Most hoisting jobs use a safe working load based on a 5:1 safety factor of the wire rope's breaking strength. However, this safety factor should be even higher if there is a possibility of injury or death from the rope breaking. For example, eleva- tors are based on a 20:1 safety factor. Critical lifts with a dan- ger to personnel should be calculated on a 10:1 safety factor. Wire Rope Inspection Wire rope inspections are important checks on any type of rigging equipment. Wear, metal fatigue, abrasion, corrosion, kinks, and improper reeving are more important in dictating the life of a wire rope—more so than its breaking strength when new. Therefore, wire rope should be regularly inspected in accordance with OSHA and industry standards. The frequency of inspections depends on the service condi- tions. Slings should be inspected each day before being used. Wire rope in continuous service or severe conditions should be inspected at least weekly and also observed during normal operation. For most other applications, wire rope should be inspected at least monthly. Wire rope should be inspected for the following conditions: Broken wires: Removing a wire rope from service due to broken wires depends on how the particular rope is being used. Finding one broken wire (or several widely spread) is usually not a problem. Regular breaks are a cause for concern and require a closer inspection. General guidelines for rope replacement due to broken wires are as follows: Running wire ropes: Six randomly distributed broken wires in one rope lay or three broken wires in one strand in one rope lay, where a rope lay is the length along the rope in which one strand makes a complete revolution around the rope. Pendants or standing wire ropes: More than two broken wires in one rope lay located in the rope beyond end connections or more than one broken wire in a rope lay located at an end connection. Slings: Ten randomly distributed broken wires in one rope lay or five broken wires in one strand in one rope lay. Rotation-resistant ropes: Two randomly distributed broken wires in six rope diameters or four randomly dis- tributed broken wires in 30 rope diameters. Valley breaks: Wire ropes with any wire breaks in between two adjoining strands should be removed from service. Abrasion: Wire rope winding over drums or through sheaves will wear. The rope should be replaced if the outer wire exceeds one-third of the original diameter. SAFETY MATTERS SAFE USE OF FIBER AND WIRE ROPES Understand their conditions, concerns, and care. 34 February 2016 WWJ waterwelljournal.com JEROME E. SPEAR