Rigging
Rigging is the process of material handling, installing or moving or relocation of structural components by lifting or rolling using hoisting tools like block and tackle, wire ropes, tumbuckles, clevis, jacks used with cranes and other lifting equipment.
Rigging plan
Rigging plan is developed every time a heavy load is being lifted. Basic idea behind a rigging plan is to have control and establish safety precautions. Important planning process that will identify all hazardous situations that might be encountered during lifting.
Types of rigging plan
Three major classification of lifting plans are critical lifts, ordinary lifts and pre engineering lifts. Depending on the type of lift, then the rigging plan will have different concept under evaluation to determine the steps needed to complete a safe rigging and lifting process.
Ordinary lifts
Ordinary lifts are the easiest ones to handle. They will normally require a verbal planning process and preliminary lifting and rigging meetings. Only a minimal documentation and evaluation process is needed, but always being sure that all safety precautions are being taken.
Critical lifts
Critical lifts need a more detailed plan before execution. This process will normally require a written procedure and approval process.
Pre engineering lifts
These are the most challenging ones to deal with. They will require specific rigging points, lifting procedures and identification of components that will probably need to be managed separately, to avoid problems and minimize the potential issues.
Rigging and lifting plan components
Once the evaluation process has determined the type of rigging and lifting plan needed, identify and gather information on the following components.
1) The rigging equipment
2) Shackles, tumbuckles and slings being used
3) The weight being lifted
4) Center of gravity of the load being lifted
5) Crane capacity and crane charts
6) Height, width and length of the lift
7) Atmospheric and environmental conditions when the process is being performed
8) Edges and corners of the load is important to evaluate all the geometry of the item being lifted
9) Sling angles
10) Load angle factor
11) How to rig the load using good rigging practices
12) Flood loading capacity
13) Identify and make sure that the attachment points and load can withstand the forces created by the rigging gear attachment
14) Work zone safety
15) Evaluate hazards to determine consequences resulting from a collision, upset or dropping the load
Execution of rigging plan
Once the plan has been established you will need to follow it closely to reduce the probability of an accident. It is important to
1) Verify all equipment, fixures and accessories before starting
2) Verify that all equipment has been properly inspected and that suck inspections are valid.
3) Identify a load manager or a rigging loader. It can be your safety professional or ordinary lifts, assign a designated leader, for critical lifts, assign a person in charge
4) Conduct a pre use inspection and verify that all the components are in good condition
5) Conduct a dummy rigging process following the pre established rigging plan
6) Be sure to identify and train all workers participating in the process
7) Clear or prepare the areas where the load is being placed or moved
8) Survey the lift site for hazardous or unsafe condition
9) Clear lift path of constructions
10) Identify the crane operator
11) Follow specific instructions or procedures for attachment of the rigging gear to the load. Use proper rigging techniques
12) Stop the job when any potentially unsafe condition is recognized
Rigging components
The following are the components of rigging
1. Ropes, chains, synthetic web slings, metallic mesh sling
2. Slings
3. Hatches
4. Blocks
5. Shackles
6. Lift lugs, eyebolts and swivel eyes
Ropes
Ropes are commonly used tool in hoisting and rigging operation. Rope may be used ad slings for hoisting materials, handlines for lifting light loads, taglines for helping to guide and control loads. The fibres in these ropes are either natural or synthetic.
Chains
Chains are suited for applications requiring flexibility and resistance to abrasion, cutting and high temperatures. Alloy steel chain grade 80 is marked with an 8, 80 or 800 grade 100 is marked with a 10, 100 or 1000. Alloy steel chain is the only type which can be used for overhead lifting. Chain slings must have a design factor of 5.
Synthetic web slings
Nylon slings are available in two materials nylon and polyester. Nylon slings are more common but polyester slings are often recommended where headroom is limited since they stretch only half as much as nylon slings. Relative softness and width create much less tendency to mar or scratch finely machined, highly polished or painted surfaces and less tendency to crush fragile objects than fibre rope, wire rope or chain slings. Because of their flexibility they tend to mold themselves to the shape of the load.
Metal mesh slings
Metal mesh slings also known as wire or chain mesh slings are well adapted for use where loads are abrasive, hot or tend to cut fabric slings and wire ropes. They resist abrasion and cutting grip the load firmly without stretching and can withstand temperature upto 550 degree centigrade. They have smooth, flat bearing structures, conforming to irregular shape, do not lint or tangle and resist corrosion.
Slings
Flexible lifting attachment used with crane hook, main component. Slings come in any number of shapes, sizes, capacities and types. Lifting slings and rigging slings can be categorized into three general types based on construction and design: nylon or polyester web sling, steel wire rope sling and chain sling. All slings regardless of type must have a legible tag starting, among other things, its safe working load when in a straight pull.
Hitch
Hitch is the manner of using the sling to support the load. Irrespective of the number of the slings the type of hitches used or the use of spreader bars, the center of gravity of a suspended load always lies directly beneath the point of attachment to the lifting device. Slings and hitches must be chosen properly to achieve the desired orientation of the hanging load, the desired stability, and desired rope factor of safety.
Blocks
A block is a frame that encloses one or more sheaves and is provided with a hook or some other means that allows attachment to cargo or to a fixed anchor point. The purpose of a block is twofold. First, it is used to change the direction of a wire rope line. Secondly, when used in pairs, blocks increase mechanical advantage by allowing the use of multiple parts of line.
Hooks
Most hooks are constructed from forged alloy steel and are stamped with their rated safe working loads. The SWL applies only when the load is applied to the saddle of the hook. When the hook is eccentrically loaded, hook capacity SWL must be reduced. All hoisting hooks must be equipped with safety catches.
Shackles
Shackles are the primary devices that are used to attach slings to equipment lifting lugs.
Load attachment devices
There are primarily three devices used to attach rigging to a load. They are lugs, eyebolts, an swivel eyes.
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