Millwright Certification Rigging Techniques 2 — Questions and Answers

Question 1: What is the purpose of a tag line when performing a crane lift?

To identify the load's weight
To control the load's rotation and prevent it from spinning or swinging during the lift (Correct answer)
To increase the crane's lifting capacity
To measure the height of the lift

Correct answer: To control the load's rotation and prevent it from spinning or swinging during the lift

Tag lines are ropes attached to the load that riggers hold to control the load's orientation, preventing it from spinning, swinging, or contacting structures during lifting and travel.

Tag lines are essential safety tools in crane operations. They allow ground personnel to: control load rotation, guide loads around obstacles during travel, position loads precisely for setting, and keep the load from contacting structures or personnel. Rules include: use non-conductive tag lines near electrical hazards, never wrap tag lines around hands or body, maintain at least two tag lines on large or awkward loads, and never stand under a suspended load while managing a tag line.

Question 2: What is the safe working load (SWL) of a sling, and how does it relate to the breaking strength?

SWL and breaking strength are the same value
SWL is the maximum load a sling can safely lift, calculated by dividing the breaking strength by a safety factor (typically 5:1 for wire rope slings) (Correct answer)
SWL is always double the breaking strength
SWL is determined by the sling color

Correct answer: SWL is the maximum load a sling can safely lift, calculated by dividing the breaking strength by a safety factor (typically 5:1 for wire rope slings)

Safe Working Load (SWL) or Working Load Limit (WLL) is the maximum load a sling is rated to lift in normal service. It equals the breaking strength divided by the design safety factor (typically 5:1 for wire rope, 5:1 for chain).

SWL/WLL represents the maximum allowed working load including all dynamic factors. Safety factors provide a margin for: dynamic loading, wear and degradation, load distribution uncertainties, and D/d ratio effects. Standard safety factors: wire rope slings 5:1, alloy chain slings 4:1 or 5:1, synthetic web slings 5:1, and synthetic round slings 5:1. NEVER exceed the rated SWL/WLL. Slings must be inspected before each use and removed from service if damaged.

Question 3: How does the sling angle affect the load on each leg of a multi-leg sling arrangement?

Angle has no effect on sling loading
As the sling angle from vertical decreases (spreads wider), the load on each sling leg increases due to the horizontal force component (Correct answer)
Wider angles reduce the load on each sling leg
Sling angle only affects balance, not load

Correct answer: As the sling angle from vertical decreases (spreads wider), the load on each sling leg increases due to the horizontal force component

As sling legs spread wider from vertical, each leg must carry more load to produce the same vertical lifting force. At 60 degrees from vertical, each leg carries the full load weight; at 45 degrees, each carries 1.41 times its share.

The sling angle factor is based on trigonometry. Each sling leg must provide a vertical force component equal to its share of the load, but the total tension in the leg equals that vertical component divided by the cosine of the angle from vertical. At 0 degrees (straight vertical): tension = 100%. At 30 degrees: 115%. At 45 degrees: 141%. At 60 degrees: 200%. The industry minimum sling angle is typically 45 degrees from horizontal. Always consider the actual sling angles when calculating rigging requirements.

Question 4: What is a basket hitch, and when is it appropriate to use?

A hitch used only for lifting baskets
A sling passed under the load with both ends attached to the hook, doubling the sling capacity for loads that are stable and balanced (Correct answer)
A decorative knot for lifting
A basket hitch is the same as a choker hitch

Correct answer: A sling passed under the load with both ends attached to the hook, doubling the sling capacity for loads that are stable and balanced

A basket hitch passes the sling under the load and attaches both end fittings to the crane hook, effectively creating a U-shaped cradle. This configuration doubles the sling's rated capacity because the load is shared between two legs.

In a basket hitch, the sling passes under the load and both ends connect to the hook, creating two vertical legs sharing the load. Requirements: the load must be stable and balanced, the contact points must be able to bear the concentrated sling load, both legs must seat in the hook properly, and the D/d ratio must be adequate. The basket hitch is NOT appropriate for: loads that could roll or shift, bundles that could spread apart, single items that could slide out the sides, or loads with sharp edges that could cut a synthetic sling.

Question 5: Before performing any lift, what is the first thing a rigger must determine?

The color of the crane
The weight of the load, including the weight of rigging hardware attached to it (Correct answer)
The time of day
The names of all personnel in the area

Correct answer: The weight of the load, including the weight of rigging hardware attached to it

Knowing the exact weight of the load (plus rigging hardware) is the fundamental first step in any lift plan because all rigging selections (crane capacity, sling ratings, shackle sizes, and rigging configuration) depend on the load weight.

Load weight determination is the foundation of safe rigging. Methods include: shipping documents or manufacturer data plates, engineering drawings with material specifications, calculations from dimensions and material density, and certified scales for critical lifts. Always add the weight of all rigging hardware (slings, shackles, spreader bars, headache ball, hook block) to the load weight: this combined weight must not exceed the crane's rated capacity at the working radius.

Question 6: What is the danger of using a damaged or kinked wire rope sling?

It may change color
Damage concentrates stress at the defect, drastically reducing the sling's capacity below its rating and creating an unpredictable failure point (Correct answer)
Damaged slings are stronger because they have been work-hardened
Kinked slings just look bad but work fine

Correct answer: Damage concentrates stress at the defect, drastically reducing the sling's capacity below its rating and creating an unpredictable failure point

Kinks, broken wires, crushed sections, and corrosion all reduce the wire rope's cross-sectional area and create stress concentrations where failure can occur suddenly at loads well below the rated capacity.

Wire rope slings must be inspected before each use and permanently removed from service when defects are found. Removal criteria include: 10 or more broken wires in one rope lay, 5 or more broken wires in one strand, any broken wires at end fittings, kinks, crushing or birdcaging, core protrusion, heat damage, corrosion, reduction in rope diameter exceeding 5%, and damaged or deformed end fittings. A kinked wire rope has zero structural integrity at the kink. Tagged-out slings must be destroyed to prevent re-use.

Millwright Certification Rigging Techniques 2

What is the purpose of a tag line when performing a crane lift?