When the pipeline is slack, and then begins to pack, how exactly does ATMOS identify this as an operational change rather than a leak?

The fluid compressibility is included in the mass imbalance calculations through the use of flow and pressure measurement data. Inventory changes due to fluid compressibility can be represented by pressure variations during most operating conditions.

When pumping into a slack line, the inventory will increase in the line as it packs. Thus, the inlet flow will be greater than the outlet flow. However, the pattern recognition tool will identify that the pipeline pressure is increasing as the line packs, thus ATMOS will know that this is an operational change not a leak.

If this were a real leak, the inlet flow will be greater than the outlet flow, but the pipeline pressure will not increase. Thus, the pattern recognition tool will identify it as a leak.