Pipeline Monitor (PLM) transient operations

Packing and/or unpacking takes place during transient operations. Packing in a pipeline section is caused by either an increase in the fluid entering the section, or a decrease in fluid leaving the section. In either case, Vin exceeds Vout. During a packing operation the volume difference is negative, resulting in a pressure and linepack increase. During an unpacking operation, the opposite is true: the volume difference is positive and linepack decreases. The mass balance principle dictates that the volume difference is the same as the linepack change in both packing and unpacking operations, unless there is an unaccounted flow such as a leak. As shown in the Signature Plot figure (see Upstream / Downstream Pressure Control Only), packing appears as a diagonal line in the fourth quadrant, and unpacking as a diagonal line in the second quadrant.