Petroleums. Fig 21.-Relation of Viscosity to Temperature of Typical Crude

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STORAGE OF PETROLEUM.

Petroleum is usually stored above ground in cylindrical steel or iron tanks of convenient proportions for requirements. A roof is provided to prevent admission of rain water and contamination. In the case of light oils evaporation losses are diminished by the use of an air tight roof but in the latter case, a special equilibrium valve is needed to allow the escape of the gas if the pressure exceeds a predetermined safe degree and to admit air when oil is abstracted. The main features characterizing an oil tank are:

1. Large draw-off valve at lowest point to remove water and sediment.

2. One or two manholes near base for entry.

3. Inlet pipe leading above top of tank and either discharging on base or flowing into second large pipe that conducts new oil to the base of tank and prevents undue splashing and consequently liberation of light products.

4. Gauge glass or succession of gauge glasses to read off oil level. 5. Sometimes a float and outside measuring board and indieator to show level of liquid.

6. Floating or adjustable suction pipe to draw oil from top of liquid when discharging.

7. Sometimes for light oils in hot climates a water spray for roof or a dished roof for holding water.

8. The construction of an earthen embankment round the tank enclosing a space from one and a half to twice the volume of the tank so that in the event of a fire, the burning oil may be prevented from spreading.

9. All oil tanks should be painted outside: the finishing coat should be white or nearly so in a hot climate to prevent undue absorption of heat.

10. Oil tanks, especially when intended for light gravity oil, should be very closely riveted, and great care should be taken to close the seams before the rivets are inserted and driven.

11. One or more dipping pipes, sometimes combined with the escape valves are usually fitted for sampling.

The cost of steel tankage varies with the price of metal and labor, but for standard sized tanks the price varies from about $1.00 per barrel of capacity for 1,000 barrel tanks to $0.30 per barrel for 55,000 barrel tanks (1921).

LOSSES IN THE STORAGE OF CRUDE PETROLEUM.

The principal losses in the storage of crude petroleum are due to evaporation, to fire and to seepage.

Oils having the greatest loss are the crude oils containing the most gasoline, since they are the most volatile, most readily form explosive and inflammable mixtures and due to their low viscosity most readily flow through walls of loose texture.

The loss from evaporation is greater the larger the amount of gasoline. The loss also depends upon the temperatures of storage and upon the amount of surface exposed to atmospheric circulation. If the tank or container is perfectly tight, then there will be no loss by evaporation.

There are three general types of storage now in use in the MidContinent fields;-the earthen reservoir, the steel tank with wooden roof and the steel tank with a steel, gas-tight roof.

The 55,000 and 35,000 barrel steel tanks are the usual sizes. Altogether there are more than 3500 of these large steel tanks in use in the Mid-Continent field.

The earthen storage is extremely wasteful from both seepage and evaporation. Petroleum standing in this type of reservoir has been known to shrink 40% in volume in two or three weeks. The shrinkage in value is of course much greater as the portion lost by evaporation is the best of the gasoline.

The following losses by evaporation took place in steel tanks with no seepage, with wooden roof covered with paper and tarred and apparently tight. The oil was of 40° Be' gravity and the tanks were of a diameter of 114% feet.

The above figures indicate that there might be a loss of 1% per month of storage in wood roof steel tanks and this might amount to as much as 6,000 barrels per year per tank.

It has been claimed that oil stored in white tanks is subjected to 1 to 12% less evaporation than in red tanks and 22% less evaporation than in black tanks.

Various types of insulation have been used with success.

A typical storage temperature for the Mid-Continent field for oil stored above ground would be 80° F. A typical temperature of the ground for a submerged tank would be 60° F. which would more nearly approach the storage temperature of the air for the whole year.

If tanks could be successfully and cheaply built in the ground, they would have the advantage of almost perfect insulation from outside heat, and the oil would be stored at practically the temperature at which it comes from the ground. For this submerged type of tank, concrete construction would be proper if capable of perfect construction. It should be monolithic, well reinforced and lined with a coating impervious to water and gasoline.

APPORTIONMENT OF THE LOSS SUSTAINED BY CRUDE ON ITS JOURNEY FROM THE WELL TO THE REFINERY. Per Cent Volume Evaporated.

Next in quantity after the evaporation losses in the storage of crude oil is the loss due to fire. Petroleum fires destroyed 12,850,000 barrels of oil in the United States in 1918. From January 1, 1908, to January 1, 1918, approximately 12,850,000 barrels of oil and 5,024,506,000 cubic feet of gas were destroyed by fire in the United States entailing a total estimated property loss of $25,254.000. During this period 503 fires were reported. Of these fires 310 were caused by lightning and 193 by other causes. The losses from the fires caused by lightning were estimated to be $11,148 000 and from those due to other causes, $14,106,200. Directly and indirectly the fires resulted in the deaths of nearly 150 persons and were responsible for almost as many more being permanently disabled.

Loss from fire in the oil field storage in the year 1916 amounted to about $4,000,000.

air.

The causes of fires are electrical discharges or open flames in the presence of an inflammable or explosive mixture of gasoline and The amount of gasoline vapor in air necessary for an explosive mixture is within the limits of 12 per cent and 5 per cent by weight. Less than the lower limit or more than the upper limit will not ignite. open tank if the amount at the surface of the oil exceeds 11⁄2 per cent there is at some point an explosive mixture and an igniting temperature of 900 degrees F. or over will cause it to take fire. perfectly tight tank with gasoline vapor in excess of the upper limit for an explosive mixture, there will be no fire unless the roof of the tank is open at some point.

In an

In a

The ingress of a flame through an opening may be prevented in the same way that the flame in the Davy miner's lamp is prevented from passing outward. This operates by having some metal screen or other material cool the flame and prevent it being propagated into the tank. This will not prevent ignition from an electrostatic discharge in the vapor space of the tank.

Methods for prevention of fires of oil in storage are as follows: 1. Means of preventing the passage of the spark in a portion of the unfilled space of the tank.

2. The maintenance of a mixture in the unfilled portion of the tank which is not an explosive mixture.