This paper examines the mechanisms of electromagnetic interference between a power line and a neighboring pipeline. An electromagnetic field theory approach is used to carry out the study. First, the field theory approach is used to model the complete conductor network under consideration as is. The inductive, capacitive and conductive interference effects between all the elements in the network are simultaneously taken into account in one single step. The computed results are then used to develop a network model whereby the inductive, capacitive and conductive interference effects can be separated. This approach allows one to better understand the effects of each individual component and compare the field-theory (inductive) based results with those obtained from a circuit model approach. The effects of a typical mitigation system on the interference levels are also studied. The results presented in this paper clearly illustrate the mechanisms of electromagnetic interference and mitigation between electrical networks and neighboring metallic utilities.