CHAIN INSPECTION

First, you must be aware that chains normally stretch under excessive loading and individual links will be bent slightly. Therefore, bent links are a warning that the chain has been overloaded and may fail suddenly under load. Before lifting with a chain, make sure the chain is free from twists and kinks. A twisted or kinked chain placed under stress could fail even when handling a light load. Additionally, ensure that the load is properly seated in the hook (not on the point) and that the chain is free from nicks or other damage. Avoid sudden jerks in lifting and lowering the load, and always consider the angle of lift with a sling chain bridle.

The strength of any chain is negatively affected when it has been knotted, overloaded, or heated to temperatures above 500F.

Figure 6-19.-Determination of double-basket hitch sling capacity.

Figure 6-20.-Determination of single-choker hitch sling capacity.

CHAIN SAFE WORKING LOADS

To determine the safe working load on a chain, apply a factor of safety to the breaking strength. The safe working load is ordinarily one-sixth of the breaking strength, giving a safety factor of 6 (table 6-1).

The capacity of an open link chain can be approximated by using the following rule of thumb: SWL = 8D' x 1 ton

Where:

D = Smallest diameter measured in inches SWL = Safe working load in tons Example:

Using the rule of thumb, the safe working capacity of a chain with a diameter of 3/4 inch is as follows: SWL = 8D2= 8 (3/4)2= 4.5 tons (or 9,000 lbs) These figures assume the load is being applied in a straight pull, rather than an impact. An impact load is when an object is suddenly dropped for a distance

Figure 6-21.-Determination of double-choker hitch sling capacity.

Figure 6-22.-Stress on slings at various vertical angles.

Table 6-1.-Safe Working Load of Chains

and stopped. The impact load is several times the weight of the load.

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