Lifting & Hoisting
How can we help?
As Lifting & Hoisting Specialists, we believe in a structured process to ensure predictable outcomes in Lifting & Hoisting Operations. For Critical Lifts, let us develop a Lift Engineering Package for you. Lift-Engineering Packages should include all necessary engineering to support a lifting operation. Depending on the criticality and complexity of the lift, the package may include some or all of the items below:
- Crane Layout Drawings
- Rigging Arrangement Drawings
- Crane Clash Checks
- Padeye or Spreader Bar Design
- Ground Bearing Pressure Calculations
Why do you need a Lift Plan?
Lifts should be categorized to ensure the effort put into planning is aligned with the risk of the operation. The categorization is determined by assessing the lift against parameters that impact probability or consequences of failure. Some examples of criteria are listed below:
- Lifted Load
- Number of Cranes
- Utilization of Crane
- Experience of Operator
- Personnel Lifting
- Unknown Ground Conditions
- Lifted Load is High Cost or Long-Lead Time
Categorization typically begins with a Routine Lift for the lower risk operations and progresses to a Critical or Engineered Lift for the operations of highest risk. The level of effort put into the planning effort should be directly related to the risk categories. Like seasoned operators sit in the cab for the most complex lifts, additional planning and field oversight should be assigned to high risk operations. Developing a standard categorization eliminates the subjectivity of risk.
The Lift Engineering Package and Operations Manual described below are related to a High Risk lift operation. For Medium and Low Risk, a more simplified version would be compiled that is specific to the risks involved in the operation.
This will include a sketch of the lifted item, including attachment points, weight, and center of gravity (CG). This crucial information should come from a reliable source, and the person responsible for development of the lift-engineering package should verify this information using practical means respective to the risk of the operation. Selecting the proper lift points will be dependent on the strength and geometry of the lifted item, location of the CG, and the number of cranes available for the lift. Once the lift points have been determined, a rigging arrangement sketch will be developed illustrating the geometry and capacity requirements of the individual rigging components.
Rigging includes everything between the lifted item and the crane hook. The rigging calculations will specify the part and model number of the individual rigging components from a manufacturer’s catalog, or simply state the capacity requirements leaving the field to select the specific rigging from their inventory. Rigging calculations should always adhere to the Safe Working Load (SWL) or Working Load Limit (WLL) of manufactured parts, with special consideration taken for any capacity reductions. Capacity reductions can be specified by the manufacture, such as shackles loaded out of plane, but they can also be industry practices, like the D/d ratio reduction when a sling is used in a basket arrangement causing high stress at the bend. The load in the rigging is calculated using the expected geometry of the rigging arrangement. These loads account for the weight of the rigging below each component as well. Wire rope slings are specified to the proper level of detail. The strength of the steel (XIP), the number and braid of the wires (6x19), and the type of strand center (IWRC) all impact the capacity.
Lift Aid Analysis or Design
The lifted item may have structural points designed to attach the rigging, or structural lifting frames/bars to achieve the desired rigging arrangement. Proper structural analysis will be performed on these lift aids to ensure a successful, safe lift. These lift aids should be designed for the maximum expected load of the lifted item and the worst case center of gravity. The loads can vary if the lifted item is dry or filled with operating liquids. The direction and magnitude of the load can vary if the lifted item is being rotated or flipped during the lift operation. The designer may also apply factors to the load to account for repetitive uncontrolled use, dynamic loading, criticality of the lifted item, potential for personnel harm, etc.
- Spreader Bars are a component in a rigging arrangement that allows for multiple direct vertical slings to hoist a lifted item utilizing fewer cranes than lift points. The most traditional arrangement of a spreader bar would include a bridle sling arrangement above the bar connecting to the crane hook, with two vertical slings attached to the lifted load below the bar. Spreader bars are primarily taking the compression load from the bridle sling arrangement, but can also experience some bending moment due to the eccentricity of the shackle pins. This eccentricity can be designed out of the spreader bar resulting in a very efficient bar for the expected load. Multiple spreader bars can be combined into a single rigging arrangement for more complex lifts. Ultimately, they minimize the number of cranes required for a lift.
- Padeyes are structural plate components that are designed to receive a shackle pin. These are typically fixed welded parts of the lifted load but are commonly seen as removable bolted connections as well. Padeyes are most commonly connected to flat plate structural members of the lifted load, but they can be attached to any type of member with some stiffening support potentially required. Padeyes may have cheek plates welded to each side of the main plate to increase the bearing capacity or similar local strength around the pin hole. Cheek plates are also called donut plates which helps describe their shape. Cheek plates may also be utilized to ensure even shackle loading along the axis of the main plate. This prevents additional out-of-plane bending on a padeye due to the main plate not being aligned with the centerline of the shackle. Careful consideration must be made for the weld of the cheek plate to the main plate. Due to fabrication tolerances, the cheek plates may end up taking more load than expected, resulting in high stresses on your cheek plate weld. This can be addressed during fabrication by either specifying a tight tolerance on hole alignment, or requiring the holes be line bored after the cheek plates are welded. Multiple industry standards exist to assist with padeye design.
- Trunnions are a pipe structure attached to a lifted load allowing for a sling connection in a basket arrangement. Trunnions are commonly used when lifting a structure comprised of tubulars. The tubular-to-tubular connection allows for a better transfer of load than a padeye plate to tubular. Trunnions may also be utilized when you need the lifted load to rotate 180 degrees or beyond. Trunnions should be designed with ears or an end cap to prevent the basket sling from slipping off the end. During a rotation of a load, the trunnion may be greased to lower the friction force between the sling and trunnion.
- Manufactured Lift Aids can include items such as eyebolts, swivel hoist rings, magnet lifters, plate hooks, pipe grabs, (look up more), and many others that make lifts simpler and more efficient. Before specifying these lift aids, the lift planner must fully understand the limitations specified by the manufacturer, and ensure these are communicated to the field operations personnel.
The package includes a sketch of the crane relative to the lifted item (load), in both plan and elevation view. Both views should include the start and finish locations of the load, and/or the minimum and maximum reaches required for the crane. These illustrations will identify any potential clashes between the load, rigging, crane, and surrounding objects.
Through the lift operation, the crane capacity should be checked against the weight of the rigging and load, including any crane take-off weight. The crane main block, hoist lines, auxiliary block, auxiliary boom extension, etc. should all be accounted for when calculating the utilization of the crane. If the route of travel or swing is uncertain, the maximum allowable radius of the crane should be specified to the field execution team.
A crucial step that is often overlooked is the verification of the ground capacity for the crane. Improper ground condition is a leading cause of lifting operation failures and should never be left unchecked. This analysis is most relevant when performing lifts at sites with no prior experience, or known poor soil conditions. Proper sampling should be performed to determine matting or piling requirements.
Lift Operations Manual (or Method Statement)
The Lift Operations Manual should communicate the engineering intent and boundaries to the field execution team. The operations manual should include a step-by-step description of the lift operation, rigging arrangement drawings, expected lifted load & CG, min/max crane radius, hazard identification, weather restrictions, tag lines, lines of communication, and barricade requirements. This document should be reviewed with all personnel involved in the operation prior to the lift to ensure all proper preparations are in place.