Rigging, Hoisting, and Lifting Equipment

Rigging, Lifting, and Lifting Equipment

Introduction to Industrial Lifting

Rigging and lifting are essential parts of the industrial mechanic (millwright) trade. In Canada, federal and provincial standards require that all lifting work be planned, executed, and verified according to strict rules. This chapter covers the fundamental principles, load calculations, types of slings, lifting accessories, mandatory inspections, and safe procedures you must master for the Red Seal exam.

Learning Objective: By the end of this chapter, you will be able to calculate the effective capacity of a lifting system, select the appropriate equipment, interpret relevant CSA standards, and identify hazardous conditions.

Fundamental Principles of Lifting

Gravity and Load

Any suspended load exerts a downward vertical force equal to its mass multiplied by gravitational acceleration (g = 9.81 m/s²). In industrial practice, the relationship used is:

Force (N) = Mass (kg) × 9.81 m/s²

However, in the lifting field, you typically work in kilograms (kg) or metric tonnes (t) for mass, and in newtons (N) or kilonewtons (kN) for forces. The common conversion: 1 kg = 9.81 N ≈ 10 N (practical rounding).

Centre of Gravity

The centre of gravity (CG) is the point where all of an object's mass is considered to be concentrated. For a safe lift, the CG must be located directly below the main attachment point (the hook of the overhead crane or hoist). If the CG is offset, the load will tip or pivot.

Rule of thumb: The rigging point must be above the CG. The greater the horizontal distance between the attachment point and the CG, the higher the risk of tipping.

Sling Angles and Tension

The sling angle is the angle formed between the sling leg and the horizontal. This angle determines the tension in each leg. The smaller (more acute) the angle, the greater the tension.

Tension formula per leg:

T = (Total weight ÷ Number of legs) ÷ sin(θ)

Where θ (theta) is the angle between the leg and the horizontal.

Example: A 1000 kg load suspended by 2 legs at a 45° angle:

Table of tension factors (multiplier)

Golden rule: Never use an angle less than 30° with the horizontal. Below 30°, tension increases exponentially and the risk of failure is major.

Rated Load and Effective Capacity

The rated load (or safe working load — SWL) is the maximum load that equipment can support under ideal conditions, as specified by the manufacturer. The effective capacity is the rated load adjusted for actual conditions: sling angle, mode of attachment, temperature, wear, etc.

General formula:

Effective capacity = Rated capacity × Angle factor × Mode factor × Temperature factor

Types of Slings

Chain Slings

Chain slings are made of alloy steel (typically Grade 80 or 100) and are used for heavy loads, high temperatures, and sharp edges.

Advantages:

Disadvantages:

Applicable standards: CSA B167 (Safety of overhead cranes and monorails) and ASME B30.9 (chain slings).

Inspection: Check each link for deformation, cracks, corrosion, and wear. Measure link diameter with a caliper. A link worn more than 10% of its original diameter must be removed from service.

Wire Rope Slings

Wire rope slings consist of strands twisted around a core. They are used for heavy loads and general applications.

Rejection criteria (according to CSA and OSHA):

Safety factor: The standard safety factor for wire rope is 5:1 (the breaking load is 5 times the rated load).

Synthetic Fibre Slings (nylon, polyester, polypropylene)

Textile slings are lightweight, flexible, and do not damage finished surfaces. They are available in two types: webbing (flat) and rope.

Important limitations:

Colour codes (according to ASME B30.9 and Canadian manufacturers):

Inspection: Look for cuts, tears, open seams, burns, UV discolouration, and illegible labels. Any sling with a missing label must be removed from service.

Rope Slings (manila, polyester)

Synthetic fibre ropes are used for light loads and temporary applications. Their capacity is generally lower than that of webbing slings.

Lifting Accessories

Shackles

Shackles connect the sling to the attachment point. They are available in two main types:

Identification: Shackles are marked with their capacity in tonnes (e.g., 2 t, 5 t). The capacity is valid for an in-line load (axial tension). Any side loading significantly reduces capacity.

Rule: Never replace the original pin with an ordinary bolt. The pin must be of the same quality as the shackle.

Hooks

Lifting hooks are made of forged steel and carry the stamped rated capacity. Rejection criteria include:

The safety latch (hook latch) must be present and functional to prevent the sling from slipping off.

Rings and Swivels

Rings (or ring shackles) allow multiple legs to be connected. Swivels allow the load to rotate without twisting the sling. They must be lubricated and inspected for bearing wear.

Spreader Beams

A spreader beam is a rigid bar that keeps sling legs at a more favourable (more vertical) angle. It reduces tension in the legs and protects the load from lateral compression.

Modes of Attachment and Mode Factors

The mode of attachment describes how the sling is secured to the load. Each mode has a mode factor that modifies the rated capacity.

Choke Hitch

The sling is wrapped around the load and passes through its own eye. The mode factor is 0.75 (capacity is reduced by 25%).

Basket Hitch

The sling passes under the load and both ends are attached to the hook. The mode factor is 2.0 (two legs carry the load, but the angle at the hook must be considered).

Vertical Hitch

The sling is attached directly to the lifting point. The mode factor is 1.0 per leg.

Summary table of mode factors

Caution: The mode factor applies in addition to the angle factor. For example, a choke hitch sling at 45° will have an effective capacity = Rated capacity × 0.75 × sin(45°).

Lifting Calculations: Methods and Examples

Method for Calculating Total Load

The total load includes the weight of the equipment to be lifted, plus the weight of the accessories (slings, shackles, spreader beam, etc.), plus any additional forces (wind, suction, freezing, etc.).

Formula:

Total load = Weight of the load + Weight of accessories + Additional forces

Example: A 1500 kg pump is to be lifted with a 50 kg spreader beam and 4 slings weighing 5 kg each. Total load = 1500 + 50 + (4 × 5) = 1570 kg.

Calculating the Required Sling Capacity

Step 1: Determine the total load (weight + accessories).

Step 2: Determine the number of load-bearing legs.

Step 3: Calculate the tension per leg based on the angle.

Step 4: Apply the mode factor.

Step 5: Choose a sling whose rated capacity is greater than or equal to the calculated tension.

Complete example:

Calculating the Percentage of Capacity Used

Percentage = (Effective load ÷ Rated capacity) × 100

If the result exceeds 100%, the system is overloaded. A good lifting system should never exceed 80% of the rated capacity to allow for a safety margin.

Rule for Number of Legs and Load Distribution

When multiple legs are used, the load is not always distributed equally. If the legs are of unequal lengths or if the CG is not centred, some legs will carry more than their share. Always assume that 2 out of 4 legs carry the entire load (conservative rule).

Canadian Standards and Regulations

Canadian Electrical Code, Part I

The Canadian Electrical Code, Part I (C22.1-21) applies to electrical installations, including overhead cranes and electric hoists. Rule 8-200 requires that power supply conductors for overhead cranes be protected against mechanical damage and that control devices comply with safety requirements.

CSA B167 — Safety of Overhead Cranes and Monorails

The CSA B167 standard establishes requirements for the design, construction, installation, inspection, maintenance, and operation of overhead cranes and monorails. It requires:

CSA Z150 — Safety of Mobile Cranes

The CSA Z150 standard covers mobile cranes, including truck-mounted cranes, crawler cranes, and telescopic cranes. It specifies safety factors, testing procedures, and operator training requirements.

CSA B354 — Elevating Work Platforms

The CSA B354 standard applies to mobile elevating work platforms (boom lifts, scissor lifts). It requires operator training and daily inspection before use.

Canada Occupational Health and Safety Regulations

The Canada Occupational Health and Safety Regulations (SOR/86-304) apply to workplaces under federal jurisdiction. Part XIV deals with lifting devices and requires:

ASME B30 Standards

Although American in origin, the ASME B30 standards are widely adopted in Canada as technical references:

Inspection and Verification

Daily Inspection (before use)

Each day, before any use, the operator must check:

Periodic Inspection (monthly or quarterly)

A competent person must perform a more detailed inspection:

Annual Inspection and Load Testing

The annual inspection must be performed by a qualified person and may include:

Documentation: All inspections must be recorded in writing, including the date, inspector's name, results, and corrective actions.

Safe Lifting Procedures

Lifting Planning

Before any lift, the industrial mechanic must:

Standardized Lifting Signals

Hand signals must conform to CSA Z150 or ASME B30.5. Basic signals include:

Essential Safety Rules

Lifting Special Loads

Long loads: Use a spreader beam or two spaced attachment points to prevent tipping.

Cylindrical loads: Use cradles or choke hitch slings with protection.

Loads with suction or freezing: Allow for additional force to break suction before completing the lift.

Submerged loads: Consider buoyancy (the load appears lighter in water but becomes heavier as it emerges from the water).

Common Pitfalls to Avoid

Here are the most frequent errors on the Red Seal exam and in practice:

Summary

Review Questions (Self-Assessment)

Answers:

Normative References

This chapter prepares you for the Red Seal exam questions on rigging, lifting, and lifting equipment. Master the calculations, know the standards, and always apply the safety rules. Happy studying.