Steel Coil Securement Arithmetic
Dana is loading two steel coils on a 48-foot flatbed. Each coil weighs 21,000 lb, for 42,000 lb total. She uses four Grade 70 transport chains, each with a working load limit of 4,700 lb, routed over the top of each coil and hooked to the trailer deck. The coils are 4 feet wide and sit side by side; the chains contact the steel edges directly. She tightens them with load binders and checks that the binders are secured. The trailer's empty weight is 14,000 lb, and the tractor's steer axle is rated 12,000 lb. She plans to run 300 miles on I-65. A dock worker tells her four chains are plenty because 'each coil has two.' The first 50 miles will be on a two-lane road with rough pavement.
1. Does the four-chain arrangement meet the aggregate working load limit requirement? Show the arithmetic and state the minimum number of chains if each is rated 4,700 lb.
Read the worked answer
The aggregate working load limit must be at least 50% of the cargo weight. 50% of 42,000 lb = 21,000 lb. Four chains at 4,700 lb give 18,800 lb, which is 2,200 lb short. So the arrangement fails. Five chains would give 23,500 lb, which meets the aggregate requirement, provided they are properly attached and the load is still blocked. The dock worker's 'two per coil' rule of thumb is not the test; the aggregate WLL calculation controls. Dana must add at least one more chain or replace the chains with higher-rated ones before moving.
2. What else is wrong with the securement, and what should Dana do at 50 miles?
Read the worked answer
The chains contact the steel edges directly, with no edge protection. Sharp edges can cut or wear a chain and reduce its capacity. She should add edge protectors at every contact point and re-tighten. At 50 miles she must stop and recheck the load: chains, binders, edge protection, and coil position. Cargo can settle; a loose chain loses working load limit. After that, recheck every 150 miles or 3 hours, whichever comes first. She should also verify the trailer and axle weights are not exceeded; the total load is 56,000 lb, so axle distribution matters even if the total is legal.
3. If one coil shifts 6 inches after a hard brake, what should she do?
Read the worked answer
Stop as soon as safe, before continuing. A shifted coil means the securement has failed or loosened; the load may be unstable and the chains may be damaged. Re-block and re-secure the coil, replace damaged chains, and recheck the aggregate WLL. Do not continue to the receiver and 'fix it there.' A six-inch shift changes the load's center of gravity and can put extra force on the remaining chains.