Tanker queuing on site: turnaround times and the yard layout

Eleven tankers booked between 07:00 and 15:00, one loading bay, forty minutes per truck if everything works. The arithmetic says the last truck leaves at 14:20. In practice the last one left at 18:40, and the haulier sent a waiting-time invoice that nobody had budgeted for.

Turnaround is a layout problem wearing the costume of a scheduling problem. Most sites try to fix it with a booking sheet, and most of them find that the minutes were never in the schedule to begin with.

Where the forty minutes actually go

Break a load down honestly. Weighbridge in and out, five minutes if there is no queue. Approach and positioning, three to six. Hose connection and priming, four if the camlock is clean and the driver knows the bay. Transfer, ten to twenty depending on pump rate and tanker size. Mixing and verification, five to eight. Paperwork, three to five. Disconnection and washdown, four.

The variable parts are transfer and verification, and both are set by the plant rather than the driver. A bay that can only push 12 m³/h through a 3-inch line turns a 25 m³ tanker into a two-hour job before anything else happens. That single number explains more queuing than any booking system.

Layout changes that buy back the most time

Two things usually pay for themselves within a season. The first is a second connection point, even if it feeds the same line, because it lets one truck connect while another is still discharging. The second is a buffer tank between the mixing point and the loading arm, so the pump runs continuously instead of stopping while a batch is verified.

After that, the gains are smaller but real. A wider apron so a truck can leave without reversing. A marked stop line so drivers position correctly the first time. A washdown point that does not share a hose with the transfer line. Paperwork moved to the gatehouse so the driver is not walking to the office in wet boots.

Scheduling around the plant, not around the clock

If the plant can verify a batch in five minutes, book in fifteen-minute slots. If it takes twenty, booking in fifteen-minute slots does not create capacity; it creates a queue in the yard and a queue on the phone. Set the slot length from the actual verification time and add a buffer for the slowest truck in the fleet.

Spreading arrivals across the day helps more than squeezing them into the morning. A site that books eight trucks before noon and three after 13:00 is choosing its own peak. Where the haulier controls the booking, ask for the arrival profile rather than the total count, and negotiate on that.

Then read the demurrage clause. Most haulage contracts give a free period of thirty to sixty minutes and charge per hour after that, and most sites have never calculated how often they exceed it. A month of gate timings will tell you whether you are paying demurrage regularly, occasionally, or not at all. If you are paying it every week, the fix is in the plant, and the invoice is simply the cost of not fixing it.

The invoice that changed the layout

A site with a single bay was receiving 14 trucks a day during a wet month. Average turnaround was 95 minutes against a booked 45, and the haulier eventually billed standing time at a rate that added roughly 6 percent to the monthly haulage cost. The site’s first response was to argue about the clock.

The second response was to time three trucks with a stopwatch. The transfer alone took 68 minutes because the pump was worn and the line had a partially closed valve that nobody had noticed. Replacing the pump impeller and opening the valve brought transfer to 31 minutes. Turnaround fell to 58 minutes without any change to the booking sheet.

Before changing the schedule, measure one truck from gate to gate with a stopwatch and write down every segment. The answer is usually a worn pump, a wrong hose size or a verification step that could run in parallel. The solidification operations guide lists the bay checks in the order they usually fail.