Would you compare oranges to apples?
Fuel sales and dip readings collected for SIR Analysis are recorded at ambient temperature, so it makes sense to use delivery volumes recorded at ambient temperature. But often deliveries provided in SIR data are adjusted to 15°C (and referred to as L15 deliveries).
How does this happen?
Fuel delivery dockets must show the L15 compensated volume that was loaded into the truck at the time of dispatch. This is also what is most commonly used by sites to pay for the fuel, and is entered into the POS/BOS.
Here’s why this is an issue:
When L15 compensated deliveries are used in reconciliation data, the inventory figures make it seem as if you’ve gained fuel on delivery days. This is because of the fuel shrinkage which occurs when fuel from the tanker at one temperature is put into the underground tank at a different temperature.
This simply occurs because fuel at the terminal or depot is most commonly stored aboveground and is subject to the daily fluctuations of ambient temperature. In contrast, underground tank temperature is more consistent. The aboveground versus belowground fuel temperature differences can be as high as +/- 15°C, and vary from location to location and seasonally.
If your tank gets a lot of deliveries, and you have these “gains” of fuel on each delivery day, it will start to have an impact on your SIR Analysis results. More often than not, using L15 deliveries for your SIR data will result in tanks displaying a gaining trend.
With ambient deliveries, the inventory will not show as much of a gain on delivery days. The fuel shrinkage is not as great because the fuel is closer in temperature to the in-tank temperature.
Your closing dip readings, sales and deliveries tell us how much is in your tank. Our SIR system compares these figures to what should be in your tank and calculates the unexplained loss or gain of fuel over a certain time frame using these figures. But an accurate result requires accurate figures. This means recording ambient delivery volumes instead of L15 volumes when providing your inventory data for SIR Analysis.