Lifting Appliances and Rigging
This domain splits into two halves: which machines fall inside the regulation and how often they are inspected, and the rigging arithmetic and discard criteria that decide whether a lift is safe today.
Scope thresholds
Lifting appliances cover: hoists with rated capacity ≥0.5 t; cranes with rated capacity ≥3 t (or tower cranes with rated load moment ≥40 t·m, or ship loaders/unloaders with productivity ≥300 t/h) where lifting height ≥2 m; and mechanical parking installations of ≥2 levels.
Periodic inspection
Tower cranes, builder's hoists, cable cranes, mast cranes and mechanical parking equipment: every year. Other lifting appliances: every 2 years. Supervisory inspection applies on installation, alteration and major repair.
Rigging
- Wire-rope discard considers broken-wire count in a lay, diameter reduction (about 7%), kinking, cage distortion, corrosion and termination condition.
- Hook discard: wear at the critical section about 10%, opening increase about 15%, twist about 10°, cracks, or plastic deformation of the shank.
- Sling tension: for n legs each at angle α to the vertical, T = Q / (n·cos α). Keep the included angle between legs at or below 60° where practical.
Worked example
A 20 t load is lifted on two symmetrical legs, each at 60° to the vertical. Reasoning: T = 20 / (2 × cos 60°) = 20 / (2 × 0.5) = 20 t per leg. Each leg carries the full load - this is why a 120° included angle is prohibited in most procedures. Then select the sling: with a factor of safety of 6 for wire rope, required minimum breaking force per leg is 120 t; check the hook and shackle ratings too, since the weak link is frequently the end fitting rather than the rope.
Traps that cost marks
Using the 2-year cycle for tower cranes or builder's hoists; computing tension with the sine of the horizontal half-angle instead of cosine to the vertical; judging a hook by eye rather than by the 10/15/10° criteria; ignoring the rated capacity of shackles and swivels.