Outage Calculation Before a Hot Delivery
You are loading a 9,200-gallon cargo tank with 2% outage with regular gasoline at a terminal. Product temperature is 50°F. The forecast for the delivery area tomorrow is 100°F. The terminal's temperature correction table shows gasoline expands 2.8% over that range. The shipper's ticket says 8,900 gallons. The tank has four compartments: 2,300 gallons each. You plan to put 2,225 gallons in each compartment. The terminal's meter is calibrated, but the tank's visual gauge is hard to read. A dispatcher says 'the tank has 2% outage, so 8,900 is fine.' The load must be delivered into a station tank that is shaded until noon, then exposed to direct sun. You have a calibrated meter and a paper correction table, but no automatic temperature compensation on the loading arm.
1. Calculate the maximum safe load at 50°F and decide whether 8,900 gallons is acceptable.
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No. The outage is 2% of 9,200 = 184 gallons, so the maximum liquid volume at the highest expected temperature is 9,200 - 184 = 9,016 gallons. The table says gasoline expands 2.8% from 50°F to 100°F. At 50°F the maximum you may load is 9,016 / 1.028 = about 8,770 gallons. The shipper's 8,900 gallons is about 130 gallons too much. At 100°F it would occupy about 9,149 gallons, leaving only about 51 gallons of outage instead of 184. Your plan of 2,225 gallons per compartment is also too high: 8,770 / 4 = about 2,192 gallons per compartment. Load no more than about 2,190 gallons per compartment, and verify with the meter and gauge. The dispatcher is wrong because 2% outage is a minimum expansion space, not a target.
2. The visual gauge is hard to read. How do you verify the load, and what do you do if the terminal cannot confirm temperature?
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Use the calibrated meter as the primary measure, but do not ignore temperature. Read the terminal's correction table, record product temperature, and compute the safe volume for the highest temperature the load will see. The visual gauge is only a cross-check; if it is hard to read, do not guess. If you cannot determine temperature or volume reliably, load less than the calculated maximum and leave extra outage, or stop and ask the terminal supervisor. Never top off just to use empty space. The ticket is a request, not authorization to exceed the tank's outage limit. After loading, recheck compartment levels and document the final volume and temperature.
3. Why not fill to 8,900 gallons and let the vent handle expansion?
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Filling to 8,900 and relying on the vent is unacceptable. As the product warms, it expands; if there is not enough outage, liquid can be forced out the vent or dome, causing a spill, fire, and environmental release. In a nearly full tank, thermal expansion can also create hydraulic pressure and stress the tank. The outage space is required by design and regulation, not unused capacity. The correct response is to reduce the load to about 8,770 gallons at 50°F, or wait for cooler product or weather, and to tell the dispatcher why. If the customer needs 8,900 gallons, send additional capacity or split the delivery.