Many people think of a machine as a device with gears, shafts, belts, and assorted moving parts. Yet a wire rope is a machine—a complicated machine. A typical 6x36 construction rope has 180 individual wires in the outer strands. These wires move independently in a precise pattern around the rope’s core when it bends. Despite their durability and strength, all machines—including wire rope—wear out and need to be maintained.
Inspection of wire rope and equipment provides at least three benefits: It reveals the rope’s condition and indicates the need for retirement and replacement, provides information to help determine if the best rope construction for a particular application is being used, and assists in the discovery and correction of problems in equipment or operation that can cause costly accelerated rope wear.
Inspection and recordkeeping
Obviously, the more a crane’s wire rope is used, the more often it needs to be inspected. According to typical ASME crane standards, operators or other designated persons are required to visually inspect all wire ropes at least once each shift when in use. A qualified person is required to periodically inspect all wire ropes and keep a written record, noting any damage and recording when ropes are replaced.
Good recordkeeping helps a maintenance program do what it’s supposed to do: Keep downtime and operating costs to a minimum and promote good operating practices. By keeping accurate, up-to-date records, a complete history of the wire rope’s performance is available. Changes in service can indicate the existence of a problem—either with the machine, operators, or the rope itself. Be sure to record any unusual events that occur in the rope’s service life, which will provide a basis for judging normal rope life. However, regular inspections must still be performed to detect damage, abuse, or unusual conditions.
Focus on the key points
While completing the required inspection of the entire rope length, pay particular attention to the critical points of a wire rope. These are the points that are subject to greater internal stresses, greater external forces, or are more susceptible to wear and deterioration. Conditions leading to rope retirement normally occur more quickly at these points, so it pays to expand inspection in these important areas.
Pick-up points: These are sections of ropes contacting the sheaves or the drum when the initial load of each lift is applied.
End attachments: Rope end attachments can cause localized fatigue where the rope transitions from the operating system to the end attachment. Use an awl or ice pick to probe this area for broken wires. If more than one broken wire is found, replace the rope or cut off the affected area and reinstall the end attachment. Inspection of rope ends should include the condition of the actual end fitting. Another problem frequently encountered at end fittings is corrosion or rust. Corrosion can conceal broken wires, and if left to accumulate, can erode the surface of wires. It also will accelerate fatigue.
Drums: Check for signs of wear that could damage wire rope. For grooved drums, inspect the grooves with a sheave gauge for proper contour and look for corrugation. For smooth drums, check for wire rope corrugation. It’s also important to verify that the required minimum number of dead wraps remains on the drum and check the condition of the drum flanges.
To read this article in its entirety, check out the July/August digital issue of Lift and Access.