NCCCO Wire Rope Inspection and Replacement Criteria 2 — Questions and Answers
Question 1: What is the discard criterion for wire rope based on broken wires in one lay length?
- Any broken wire requires immediate replacement
- Six randomly distributed broken wires in one lay length, or three broken wires in one strand (Correct answer)
- Ten or more broken wires at any location in the rope
- Broken wires are only a concern if visible from the operator's position
Correct answer: Six randomly distributed broken wires in one lay length, or three broken wires in one strand
ASME B30.2 and most standards specify that wire rope must be removed from service when six randomly distributed broken wires appear in one rope lay length, or when three broken wires are found in a single strand.
The broken wire discard criteria are: six randomly distributed broken wires in one rope lay length, OR three broken wires in one strand in one lay length. A lay length is one complete helical wrap of the outer strands around the core. These criteria balance the need to remove deteriorating rope before catastrophic failure against premature discard of serviceable rope. Broken wires concentrated in one area or strand indicate localized fatigue or damage and trigger the lower threshold of three wires in one strand.
Question 2: What amount of diameter reduction from nominal size indicates a wire rope must be removed from service?
- 2% reduction from nominal diameter
- Reduction beyond specified ASME limits based on rope diameter (e.g., 3/64 inch for 9/16 to 3/4 inch rope) (Correct answer)
- Any measurable reduction from nominal diameter
- 10% reduction from original diameter
Correct answer: Reduction beyond specified ASME limits based on rope diameter (e.g., 3/64 inch for 9/16 to 3/4 inch rope)
Wire rope must be removed from service when diameter has been reduced beyond specified ASME limits for each rope diameter range, indicating loss of metallic cross-section.
Diameter reduction indicates internal wire breaks, core deterioration, or crushing that has reduced the metallic cross-section supporting the load. ASME B30.2 specifies graduated limits: 1/64 inch reduction for rope up to 5/16 inch nominal diameter; 1/32 inch for 3/8 to 1/2 inch; 3/64 inch for 9/16 to 3/4 inch; and 1/16 inch for 7/8 to 1-1/8 inch diameter ropes. Operators must use calipers to measure actual rope diameter and compare against nominal size, discarding rope that has reduced beyond these limits regardless of visible wire break count.
Question 3: What is the primary purpose of wire rope lubrication during crane operations?
- To make the rope visible against dark backgrounds
- To reduce internal friction between wires and strands and protect against corrosion (Correct answer)
- To increase the rope's coefficient of friction on drum grooves
- To change the rope's load rating
Correct answer: To reduce internal friction between wires and strands and protect against corrosion
Wire rope lubrication reduces internal friction between individual wires as the rope bends around sheaves and drums, dramatically reducing fatigue wire breaks, while also providing corrosion protection.
Wire ropes are composed of many individual wires that slide against each other as the rope bends. Without lubrication, this internal friction creates heat, wear, and micro-cracking that leads to fatigue wire breaks. Lubrication also protects wire surfaces from moisture and oxygen that cause corrosion. Most ropes are factory-lubricated during manufacturing, but field lubrication is required throughout rope life. Lubricant should penetrate into the rope interior, not just coat the surface, to be effective in reducing internal friction.
Question 4: Where on a crane wire rope are fatigue breaks most commonly found and why?
- In the center of the longest rope span
- At areas of maximum bending, especially the first sheave from the drum (Correct answer)
- At the end terminations where the rope is attached
- Uniformly distributed throughout the rope length
Correct answer: At areas of maximum bending, especially the first sheave from the drum
Fatigue wire breaks concentrate at sheave contact points, especially the first sheave from the drum, because this is where the rope experiences the greatest bending cycle frequency and bending stress concentration.
Every time rope passes over a sheave, individual wires undergo a bending cycle. The first sheave from the drum experiences the most cycles because all hoisting and lowering movements pass that point. Combined with the bending stress from wrapping around a relatively small-radius sheave, this creates ideal fatigue conditions. Inspectors must pay special attention to the rope sections at all sheave contact points and should mark rope position relative to contact zones during inspection to ensure adequate coverage.
Question 5: What is fleet angle in wire rope operations and why must it be controlled?
- Fleet angle is the angle of the rope relative to the ground
- Fleet angle is the angle between the rope path and the plane of the drum groove; excessive fleet angle causes uneven winding and rope damage (Correct answer)
- Fleet angle describes the angle of the boom relative to the mast
- Fleet angle is the rate at which new rope is added to the drum
Correct answer: Fleet angle is the angle between the rope path and the plane of the drum groove; excessive fleet angle causes uneven winding and rope damage
Fleet angle is the angle between the wire rope and the centerline of the drum groove; excessive fleet angle causes the rope to wind over itself or pile up on one end, damaging the rope and drum groove.
As the crane travels and the rope winds from side to side across the drum, the angle of the rope relative to the drum groove changes, which is the fleet angle. Maximum acceptable fleet angle is typically 1.5 degrees for smooth drums and 2 degrees for grooved drums. Exceeding these limits causes the rope to cross-wind, riding over itself and being crushed between windings, damaging both the rope and the drum. Proper sheave and anchor placement to limit fleet angle is part of crane design and must be respected during installation and operation.
Question 6: What is a wire rope core and why is it important for rope performance?
- The core is a decorative element with no structural function
- The core provides internal support to maintain strand geometry and carries part of the load; its condition affects rope performance and diameter stability (Correct answer)
- The core is only present in ropes designed for marine applications
- The core prevents the rope from rotating under load
Correct answer: The core provides internal support to maintain strand geometry and carries part of the load; its condition affects rope performance and diameter stability
The wire rope core, whether fiber core (FC) or independent wire rope core (IWRC), supports the outer strands to maintain their geometry, provides lubrication retention, and in the case of IWRC, contributes to the rope's load-carrying capacity.
Wire rope cores serve as internal support preventing the outer strands from collapsing inward under load and bending stress. Fiber cores (hemp or synthetic) are more flexible and retain lubricant well but crush more easily. Independent wire rope cores (IWRC) provide better resistance to crushing, higher metallic cross-section (greater strength), and better diameter maintenance under load, at the cost of reduced flexibility. Core deterioration from crushing, corrosion, or internal wire breaks reduces overall rope strength and is evidenced by diameter reduction and flattening of the rope section.
NCCCO Wire Rope Inspection and Replacement Criteria 2
What is the discard criterion for wire rope based on broken wires in one lay length?