Selected Questions & Answers on Rigging guidelines

1. What is rigging technology?
Rigging is the process of using hoists, ropes, pulley, slings, jacks and cranes for lifting, lowering or shifting the heavy objects.
2. Who is rigger?
A person who leads or carries out the rigging process.
3. What are the various rigging elements used in power plant?
  • Synthetic and wire ropes
  • Slings
  • Chain hoist/chain block
  • Pulley block
  • Screw and hydraulic jacks
  • Crane
  • Winch machine
  • EOT cranes
  • Derricks…etc.

4. Write a short note on rigging plan.
In order to ensure the safety of workers and the equipment involved, any operation involving the use of a lifting item to lift items must be planned thoroughly before being carried out.
Rigging Plan Involves:
1. Determination of Task and Job Site Requirements:
a. What is to be lifted?
b. Who is the in charge person?
c. What are the job site requirements?
d. What type of lift?
Ordinary Lift: Involve the use of basic hoisting equipment directly above the load. The load must also have certified lifting points to relatively easy to sling. It is repetitive in nature.
Critical Lift: Involves lifting objects in congested space, heavy objects, high susceptibility to damage and precision.
Pre-Engineered Lift: Involves use of tooling, fixtures, sketches, analyses, and written procedures for handling.
2. Characterization of Load:
It involves weight and center of gravity judgment of an object to be lifted
There are mainly two types of loads that are generally handled:
Symmetrical Load: Spare, square and rectangular type loads. These have center of gravity (C.G) at their center, so it will be very easy to handle such objects.
Asymmetrical Load: An object with an off-center C.G due to the object’s irregular shape and/or composition. These objects are difficult to handle as their C.G lies out of center.
3. Selecting the Proper Rigging Element:
After characterizing the load, proper rigging elements are selected.
  • For lifting only, chain blocks and slings are selected.
  • For lifting and shifting: Cranes.
  • For lifting precision objects, lifting belts are selected instead of wire ropes and slings.

5. What is the safe working load of 25 mm Nylon rope?
Safe working load (SWL) of Nylon rope = D X D = 25 X 25 = 625 kgs.
Where D is the diameter of rope in mm.
6. What is the smallest size of nylon rope used for lifting?
Smallest size of nylon rope used for lifting is 12 mm.
7. What is the material of composition of wire ropes and slings?
MOC of wire ropes and sling is Steel of grade 80.
8. What is the smallest size of wire rope used for lifting?
Minimum size of steel wire rope for handling loads is 5 mm.
9. How do you calculate the safe working load of steel wire ropes and slings?
SWL of wire ropes slings = 8 X D X D, Where D is the diameter of sling in inches.
10. What are the different hitches of slings/ropes? And what is the relation between sling angle & angle factor?

Vertical Hitch:
In vertical hitch SWL = Capacity of the rope/sling.
Choker Hitch:
In choker hitch, SWL = Sling capacity X 80%. i.e. sling lifting capacity will reduce by 20% of its rated capacity.
Basket Hitch:
In basket hitch, SWL of Sling = Sling capacity X 140%, i.e. sling lifting capacity increases by 40% of its rated capacity.
Relation between sling angle & its angle factor
As the sling angle decreases to the horizontal then the angle factor increases.That is for lower sling angles to the horizontal the capacity of the slings reduces.
it is maximum at 90 degree angle & minimum at 30 degree angle.Hence it is recommended that slings are not loaded at ange below < 30 degree

11. What are the different slings used in power plant rigging?
Types of Slings:
  • Eye/Eye type
  • Eye thimble
  • Thimble/Thimble
12. What are the pre-use checks to be done on Nylon and wire ropes?
  • Check its manufacturer name plate details and ensure lifting load capacity.
  • Check for strand damages; discard if more than 10% of strands are damaged.
  • Check for strand frying.
  • Check for rope knotting.
  • Check for overloaded rope (Rope which was overloaded in previous lifts should not be used for lifting at its rated SWL).
  • Check for reduction in rope diameter, wear out should be less than 10%.
  • Should not have exposed temperature more than 65 and 95 °C for synthetic and wire ropes respectively for long time.
  • Check for corrosion/rusting of wire rope.
  • Check for any scoring or abrasion marks on wire rope.
  • Check for wire end attachments damages.
13. How do you calculate the SWL of Chain block?
SWL = 80 X 0.4 X D2
Where D is diameter of load chain link.
14. What are the safe checks carried out on chain block?
Following are the inspection checks carried out on chain blocks:
  • Check tightness of block’s nut bolts.
  • Check gearing system is well operating and its lubrication.
  • Check hook of block as per hook check list.
  • Check load chain links for elongation and wear out.
  • Link 10% size less than its original diameter is discarded.
  • Check for unauthorized welding and cutting marks on chain hoist.
  • Check whether chain is in contact with acid or alkali for long time.
15. What are the safe checks carried out on hooks used for lifting?
Inspection checks of hooks:
  • Check for manufacturer identification numbers.
  • Check for cracks, nicks etc.
  • Check for unauthorized welding and grinding.
  • Check for increase in throat area (not to exceed more than 5%).
  • Check for wear out (not to exceed more than 10%).
  • Check twist from plane of un bent hook.
16. What are the different types of eye bolts used in lifting?
Straight and shoulder type eye bolts are generally used for lifting applications.
17. What is the function of turn buckle?
Turn buckles are used for leveling and distributing the loads.
18. List down the safe checks carried out before moving/shifting heavy jobs.
Following are the check points for moving/shifting heavy jobs by cranes, forklifts or Hydras:
Trained operator
  • Weight to be lifted
  • CG of load
  • Lift points
  • Crane capacity
  • Crane length, speed and boom maximum height
  • Environmental parameter’s like wind velocity, visibility and temperature
  • Travel route clearance
  • Travel floor capacity
19. What is the allowable wind speed during rigging?
It should be less than 9 meter per second
20. What do you mean by tandem lifting?
Rigging plan where two cranes are used for lifting a single object
21. What are the different types of cranes used in rigging?
  • Mobile crane
  • Tower crane
  • Gantry crane
22. What is the allowable speed of wind while working at height?
It is around 10.3 meter per second
23. What are the different synthetic web slings?
Synthetic web slings are made of Nylons & Polyesters
24. How do you decide the capacity of the web sling?
It can be decided by its width
25. What are the advantages of Synthetic web slings over other slings?
  • Flexible & can adjust as per required shape.
  • Minimize twisting and spinning.
  • Do not rust and are non-sparking.
  • Are elastic and stretch. Nylon has 6% & Polyester  has 3% stretching capacity

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