As you see, this chart shows the specific gravity ranges for the major fuels, oils and lubricants we use in
the military system. The numbers at the top of the chart are the API ranges, while the numbers at the
bottom of the chart show a few of the specific gravity ranges. As would seem apparent, the fuel, oils,
and lubricants are the heaviest petroleum products we use, and are nearly as dense as water.
b. Calculate API Gravity at 60€ F.
(1) Normally, your API gravity reading will be at some temperature other than 60€F. To
convert an API gravity reading to 60€F, we use ASTM Table 5B. The left and right margins of the table
are annotated with the temperature of the sample. The upper margin lists the API gravity readings.
(2) Once you have located the temperature value, follow the row across until you intersect the
column of your API value. The intersected value is your API gravity corrected to 60F.
See if you get the correct answer for the following set of data. Determine the API gravity at 60€F:
Observed API
Temp(F)
API
32
78
30.7
46
48
47.1
52
60
52.0
66
50
67.4
(3) Calculate Specific Gravity. The SG of a liquid is the ratio of the liquid's weight to the
weight of an equal volume of water. Again, it is a measure of the density of a liquid.
SG(fuel) = SW fuel SW water (SW water = 8.33 lb/gal)
Specific Weight, SW = Fuel Weight Fuel Volume (Pounds/Gallons)
(4) Conversion Formulas.
The following formulas are used for conversion between API
gravity and specific gravity:
141.5
141.5
API
= ------- - 131.5
SG = ----------------
SG
API + 131.5
See if you get the correct answer for the following set of data. Convert the following APIs into
SG:
API
SG
10
1.0000
40
0.8251
65
0.7201
QM5203
1-9
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