Example for Use of a Tank Inventory Difference Stream

Assume there is a tank, TANK_B, which had nonzero amounts in the flows leading into and out of the tank in the period to be balanced. Of course, the metered outflow from the tank will not exactly match the metered inflow.

You should model a special tank inventory difference stream as an outgoing stream from the tank (as in Figure 122) and mark it as being unmeasured.

Assume that the global option (Set Tank Inventory Difference Stream to Out of Service when Tank Active) is checked.

If the Set Inventory Difference Stream to OS when Active checkbox setting on TANK_B Tank is unchecked, the tank difference stream (TK_DIFF_TANK_B) is considered to be in service even though there is a nonzero transaction steam (IN_TRANSACTION_TO_TANK_B) to TANK_B. The result is that imbalance on TANK_B is distributed to the tank difference stream. This may end up being reported as apparent tank loss when in reality, it is due to normal meter imbalance.

We can improve this model by checking the Set Inventory Difference Stream to OS when Active checkbox setting on TANK_B. Now the tank difference stream (TK_DIFF_TANK_B) is automatically marked out of service and the imbalance on TANK_B is distributed only to the feed stream (FEED_FROM_TANK_B). In this example, the imbalance is distributed only to the tank’s outgoing stream. It is not distributed to the stream IN_TRANSACTION_TO_TANK_B because that comes from a receipt and you would normally define such a stream as having zero tolerance.

This improved configuration is illustrated in below.

In fact, it is possible to sum the imbalances of all tanks using a node. In the figure, a special node, TANK DIFFERENCE NODE, has been created, into which all tank imbalance streams flow. The single outgoing stream from that node shows the sum for all tanks.