8.6.3. Correction for the Effect of Temperature on the Steel Shell of the Tank (CSTH) Upright cylindrical tanks have capacity tables based upon a specific tank shell temperature. In the U.S.A. this is usually 60 ° F. If the actual tank shell temperature differs from the capacity table tank shell temperature, the volumes extracted from that table will need to be corrected, accordingly. There are four items to be considered in making this correction. Note: The following is only applicable to upright cylindrical tanks. It does not apply to spherical, horizontal cylindrical or square tanks. 8.6.3.1 Calculate the Temperature of the Tank Shell (TSH) On a non-insulated tank this is done by adding 7/ 8 or 0.875 of the product temperature to 1/ 8 or 0.125 of the ambient air temperature. For example, what is the tank shell temperature if the temperature of the product in the tank is 135 ° F and the ambient air temperature is 88 ° F?
There is no standardization on how or where to take the ambient air temperature. If the terminal has a weather station, use it. Alternatively, you could leave a cup case thermometer in a shady area for at least fifteen minutes or use a thermoprobe that has stabilized to the surrounding air. Do not take ambient air temperatures in direct sunlight or enclosed areas. On insulated tanks, the temperature of the tank shell is considered to be the same temperature as the product in the tank. 8.6.3.2 To Determine the Correction This is achieved by using the table that is printed at the back of this book. The factor can be read directly from the table. In our example, the correction for a tank shell temperature of 129 ° F is 1.00086. This table is only applicable if your capacity table was generated for a tank shell temperature of 60 ° F. If the capacity table references a different tank shell temperature, contact your supervisor for instructions.
8.6 To Calculate Gross Observed Volume (GOV) Shore Tanks This is obtained by deducting any free water (FW) from the Total Observed Volume (TOV), then multiplying the result by the Tank Shell Temperature Correction (CTSh) and applying the floating roof adjustment (FRA), where applicable.
GOV = [(TOV - FW) x CTSh] ± FRA
8.6.1 Total Observed Volume (TOV) This is the volume obtained from the shore tank's capacity table that corresponds to the observed innage or ullage. This is also referred to as the table volume. 8.6.2 Free Water (FW) It is necessary to determine the amount of free water, if any, before and after each product movement into or out of a tank in order that the appropriate corrections can be made. This adjustment will always be in the form of a volumetric deduction. The amount of the deduction is determined by converting the free water level gauge to a volume through use of the tank's capacity table.
135 x 0.875 88 x 0.125 118.13 ° F +11.00 ° F Tank Shell Temp = 129.13 ° F = =
Rounding to the nearest degree, the tank shell temperature is 129 ° F.
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