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Since riggers in the field often only have one connection point to collect slings, it's essential that they understand how to rig triangles and angles properly. A rigging triangle is formed when two or more slings are connected to a load and the other ends of the slings are collected at a common point. Whether the slings are made of chain, wire rope, or synthetic rope, the best practices for sling angles remain the same.
To begin, let's discuss some sling angle terminology. The rigging triangle consists of the included angle, the horizontal sling angle (now referred to as the "angle of loading" by ASME B30.9), and the vertical sling angle (which is simply 90 degrees minus the horizontal sling angle, and is used in some parts of the world to describe sling loading).
Here are three important points to keep in mind when it comes to sling angle best practices:
As the rigging triangle becomes flatter, the angle of loading (horizontal sling angle) becomes smaller, causing the slings to work harder as they try to lift the load and withstand crushing forces known as the resultant load.
The fittings at the load connections are subject to the same tension as the sling leg, and angular or side loading can occur. Therefore, it's crucial to select the proper size and type of rigging hardware to prevent this issue. The angle of loading should ideally be 60 degrees or larger, and the vertical sling angle should be 30 degrees or smaller (with a maximum of 60 degrees).
When using two slings with the center of gravity in the middle, the angle of loading would be at least 60 degrees if the free length of the sling is at least the same as the distance between the pick points (as shown in the illustration below).
Watch the Sling Angles Best Practice video to learn more: