Pipeline Monitor (PLM) volume imbalance

Volume imbalance can be either negative or positive.

Negative Imbalance

Normally, a negative imbalance beyond the Pipeline Monitor (PLM) alarm threshold can be considered a leak.

However, other anomalies, such as the opening of a relief valve or sump tank, or operational problems, can cause the signature line to exceed the alarm threshold. Therefore, the causes must be analyzed when any threshold is exceeded.

Positive Imbalance

Excessive positive imbalance may be caused by unaccounted gain in commodity inventory.

Unaccounted commodity gain is possible when some operational problems occur, temperature measurements are not accurate, or the contents of sump tanks or relief tanks are pumped back into the pipeline.