Sling spreader

If a spreader beam is not used, the minimum sling angle shall be 30° from the horizontal position. At 30°, the tension in each sling is equal to the total design load. Thus a load factor of 2 is mandatory for these cases. This requires that each lug be designed for the full load. 

Where production items are regularly lifted, lifting and spreader beams can be used, specially designed for the purpose. Standard lifting beams (Fig. 20.17a) or spreader beams (Fig. 20.17b) are used to give a vertical lift where the lifting points are too far apart to use slings. 

Slings and spreaders mnst not be overloaded. The optimum angle between two ropes of a sling snspended from a hook is 45 degrees. 

Ensure safe attachment of rigging devices, such as shackles, hooks, eyebolts, spreader beams and slings, wedge socket, and wire rope clips. 

Suppose you have a four-leg bridle. The loads in the slings vary because the shngs are almost always unequal in length. The loads are statically indeterminate, meaning that the true load in each shng cannot be mathematically solved. In reality, the load is carried by two slings, while the other two act to balance the load. To solve this problem, you must size the bridle such that just two legs carry the fuU load, or you must use a spreader. 

Before unloading, make sure that the thread protectors are tightly in place. The use of a spreader-bar with a choker-sling at each end is the recommended method of handhng long pipes. 

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