Six Pipes, Four Chains, and a 12,000-lb WLL Question
At a lumber yard in Tulsa, a driver is loading twelve 40-foot steel pipes, each 8 inches in diameter, side by side on a flatbed. The load weighs 24,000 lb. The driver plans to use four chain tiedowns, each rated at a working load limit of 5,400 lb, spaced evenly along the pipes and attached to the trailer's stake pockets. The pipes are not chocked or blocked. The trailer deck is 8 feet wide, and the pipes sit about 6 inches above the deck on wooden dunnage. The driver says, 'Four chains give me 21,600 lb of WLL, and half the load is only 12,000 lb, so I'm legal.' The trip is 140 miles on US-75 and I-44, with speeds up to 70 mph and a forecast of 20-mph crosswinds. The shipper's load chart says the pipes must not roll.
1. Does the four-chain arrangement meet the federal minimum number of tiedowns? Show the calculation.
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No. Under the federal cargo securement rules, an article longer than 5 feet and heavier than 1,100 lb needs two tiedowns for the first 5 feet, plus one additional tiedown for each additional 10 feet or fraction thereof. The pipes are 40 feet: 40 - 5 = 35 feet of additional length. 35 / 10 = 3.5, which rounds up to 4 additional tiedowns. That gives 2 + 4 = 6 tiedowns total.
Four chains leave the load two tiedowns short, regardless of the chains' strength. Spacing also matters: the tiedowns should be distributed to hold the pipes against shifting, and the end tiedowns should prevent lengthwise movement. The driver's 'half the load' math addresses only aggregate WLL, not the tiedown count.
2. Is the aggregate working load limit adequate? What else must the driver check about the chains and attachment points?
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The aggregate WLL is adequate: 4 x 5,400 = 21,600 lb, which exceeds the 12,000-lb minimum (50% of 24,000 lb). But adequate WLL does not cure a missing-tiedown violation, and the chains are only as strong as their weakest attachment. Check each chain, binder, and stake pocket for wear, cracks, and rating.
Also consider the 20-mph crosswind and 70-mph speed. The load's resistance to sideways movement depends on friction, blocking, and tiedown angles, not just total WLL. With six chains, plan spacing so the pipes cannot shift fore, aft, or sideways. If the attachment points are not rated for the load, the aggregate number is meaningless.
3. What should the driver add to keep the pipes from rolling, and what should he do before leaving the yard?
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Add blocking or chocks. Round steel pipes can roll even when aggregate WLL is high. The shipper's chart requires no rolling, so use wooden wedges, chocks, or a rack/contour system on both sides of the bottom tier, and tie down over the top. If the pipes are nested, block the outer pipes so the group cannot spread.
Before leaving, add the two missing tiedowns to reach six, inspect every chain and binder, and confirm the attachment points are sound. Then recheck the load after the first 50 miles and again during the trip; loads settle and chains can loosen. Do not rely on dunnage friction alone. If the driver cannot add blocking and two more tiedowns, the load is not legal and should not leave the yard.