Chain Grades
Chains are a robust tool that serves as a vital component across various industries. One of the safety measures implemented was to place chain in Grades based on the ultimate breaking strength of that chain. This number is what we see today G30, G43, G70, G80 & G100 and the common chain grades. The number after each letter is N/mm2. For example, G80 means that the maximum stress on the chain at ultimate strength is 800 newtons per millimeter squared.
Working Load Limit (WLL) of Chain
The other safety measure was identifying which types of chain are appropriate and strong enough for overhead lifting. Anytime we move or lift a load it is dangerous, but the anticipated loads can be calculated using formulae. This has resulted in 3 ‘groupings’ of chain
- General Utility: Wrapping things up and securing them in a zero risk environment often uses low carbon steel as a general utility chain for general use on farms or informal construction projects
- Along the Ground: Moving a load along the ground has the advantage that the ground is supporting the load. We have to overcome the coefficient of friction to move the load. The chain’s working load limit does not have to match the weight of the load. It needs to be able to handle the tension applied, which is based on the surface that it is being moved over plus some fraction of the weight of the load.
- In the Air: If we lift that same load off the ground, we now have to overcome gravity. The chain’s working load limit will have to be of sufficient strength to support the weight of the load plus any additional forces imposed by angles and hitch type(s) used.
Chain Grades by Application
- General Utility: Commercial (N/R) and Grade 30 (G30) are made from low carbon steel and is a general utility chain for such used as farm, log chain, tow chain and switch chain. Caution: NEVER Use for Overhead Lifting.
- On the Ground: Grade 43 (G43) and Grade 70 (G70) chain is a “heat treated” carbon steel chain that has no alloying elements added to the steel. This chain will elongate before breaking but does not have the properties needed for overhead lifting; therefore, Grade 70 chain is not intended for overhead lifting. This chain is designed for use as a tie down chain or lashing for transportation. Grade 70 chain has a gold chromate finish to help resist corrosion from continuous exposure to the elements and the rigors of highway use, such as road salts in the winter.
- In the Air: Grade 80 (G80) or Grade 100 (G100) should be used for overhead lifting. Australian Standards and ASTM state that alloy chain shall be able to elongate a minimum of 20% before fracture (7.3.5). To ensure that alloy chain consistently meets this requirement, regulatory agencies require the use of certain alloying elements in the manufacturing of the steel for alloy steel chain. These alloys can vary from company to company, but some key requirements are commonly specified (think of it as a ‘minimum’). The alloy properties also improve the wear and tear that the chain will experience. Note that when chain is in use, no amount of stretch is allowed.