Rigging Fundamentals and Hardware Flashcards

A wire rope sling has a rated capacity of 10 tons in a straight vertical hitch. When used in a basket hitch with the two legs forming a 120° included angle between them, what is the effective working load limit?

Answer: 10 tons

A basket hitch doubles the vertical-hitch capacity to 20 tons. However, a 120° included angle means each leg is 60° from vertical, giving a sling angle factor of cos(60°) = 0.5. Multiplying: 20 tons × 0.5 = 10 tons — exactly the original rated capacity. The basket hitch benefit is completely cancelled by the severe angle penalty, a classic trap on advanced rigging assessments.

A two-leg bridle sling lifts a 6,000 lb load. Each leg is 10 ft long and the horizontal spread between the two upper attachment points is 12 ft. What is the approximate tension in each leg?

Answer: 3,750 lb

Half the horizontal spread = 6 ft. Vertical height H = √(10²−6²) = √64 = 8 ft. Each leg carries half the load adjusted for angle: T = (6,000/2) ÷ (H/L) = 3,000 ÷ (8/10) = 3,000 ÷ 0.8 = 3,750 lb. The sling angle factor (0.8) increases tension above the simple half-load value of 3,000 lb, which is a common calculation mistake.

According to ASME B30.9, which condition requires a synthetic web sling to be immediately removed from service?

Answer: Any acid or caustic burns anywhere on the sling body

ASME B30.9 mandates immediate removal for any acid or caustic burns on synthetic web slings. Chemical attack degrades the entire fiber matrix, including load-bearing fibers not visible on the surface, making the sling unreliable even if damage appears localized. A single broken surface yarn, dirt discoloration, and cold-temperature stiffness alone do not meet the standard's removal criteria.

A rigger notices that a screw-pin shackle pin can be rotated by hand under no load, but the threads and bow are undamaged. What is the correct action per rigging best practice?

Answer: Mouse (seize) the pin with wire through the pin hole and around the bow, then use as normal

Screw-pin shackles are intended to be tightened finger-tight and then secured (moused) with seizing wire through the cotter hole and looped around the bow. This prevents the pin from backing out due to vibration or load shifting during a lift. The pin being turnable by hand before mousing is normal and expected — mousing is the designed prevention method. Replacing an otherwise sound shackle is unnecessary. Thread-locking compound is not an approved rigging field fix.

When inspecting wire rope, a rigger finds 8 broken wires in one rope lay in a 6×19 IWRC wire rope. What is the correct action?

Answer: Remove from service immediately — 8 broken wires exceeds the ASME B30.9 removal threshold for this construction

Per ASME B30.9, the removal criterion for a 6×19 classification wire rope is 12 broken wires in one rope lay length for running ropes, but only 6 broken wires per rope lay for standing ropes — and crucially, for 6×19 ropes, the criterion is 12 broken wires distributed across the rope OR 6 broken wires in a single strand. With 8 broken wires in one lay, further analysis of strand distribution is required, and if any single strand contains 6 or more, immediate removal is required. In practice, 8 broken wires in one lay on a 6×19 rope meets removal criteria. Derated use is never permitted for rope exceeding removal criteria.

Which of the following BEST describes the purpose of the D/d ratio in wire rope rigging, and what happens when it is too low?

Answer: D/d governs bending fatigue; a low ratio forces individual wires through a tight arc each cycle, accelerating fatigue failure

The D/d ratio (sheave or drum diameter D divided by rope diameter d) governs how sharply individual wires must bend each time the rope passes over a sheave or wraps a drum. A low D/d forces wires through a tight radius on every cycle, creating high bending stresses that cause fatigue cracking and accelerated wire breakage even when tensile loads are well within rated limits. Industry standards specify minimum D/d ratios (typically 18:1 to 34:1 depending on rope construction) to preserve service life. The catalog breaking strength is a tensile property not directly affected by D/d.