Choosing a Hitch for a Long Pipe
A 20 ft length of 12-inch diameter steel pipe, weighing 1,200 lb, must be lifted from a truck bed and set into a trench. The pipe has no lifting lugs. The rigger has chain slings and nylon slings available. The pipe's surface is smooth and slightly oily. The rigger plans a single choker hitch around the middle of the pipe. A coworker suggests a basket hitch with both legs at the center. The trench is 6 ft deep and the crane's hook height is limited.
1. Evaluate the single choker hitch in the middle of the pipe.
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A single choker in the middle of a 20 ft pipe will let the pipe rotate and tip because the hitch is at one point and the pipe's CG is at the center but the load is not balanced fore and aft. The pipe will hang like a seesaw and can slide out of the choker, especially with an oily surface. A choker also reduces the sling's capacity, typically to about 80 percent of vertical rating, and it can crush or deform the pipe if tightened too much. The rigger should not use a single choker in the middle for a long pipe; the load is unstable and the pipe can rotate.
2. Compare the basket hitch suggestion and recommend a better rigging arrangement.
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A basket hitch with both legs at the center still gives a single lifting point and does not control the pipe's rotation or fore-aft balance. A better arrangement is a two-point lift using two choker hitches placed at about one-quarter and three-quarters of the pipe's length, or a two-leg bridle with chokers at those points, so the pipe hangs level and cannot rotate. The rigger should use nylon slings with softeners if the pipe is oily, or chain slings with proper protection, and should add tag lines to control rotation. The two-point arrangement also keeps the pipe level for setting into the trench.
3. How does the trench depth and hook height limit affect the rigging choice?
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The 6 ft trench depth means the rigger needs enough hook height to lower the pipe into the trench without the slings binding on the trench edge. A two-point bridle with longer legs may reduce the available hook height, so the rigger should calculate the required hook height: pipe diameter plus sling leg vertical reach plus clearance. If hook height is limited, the rigger may need a shorter bridle or a spreader beam to keep the legs vertical and reduce the height needed. The rigger should not shorten the slings in a way that increases the angle and tension without recalculating capacity.