When overhead AC powerlines and metallic pipelines are close to each other, high AC voltages can arise on the pipeline metal due to coupling to the powerline. These voltages can present health hazards to workers and the general public. In extreme cases, the integrity of pipeline coatings and metallic walls can be affected. Our company specializes in the computer modelling of these situations as well as the design and installation of required mitigation and grounding measures.

AC power is not typically found on pipelines. If an AC voltage is present on a pipeline, it has come from one of three effects: inductive, capacitive or conductive coupling. For any of these three couplings to occur, the pipeline must be relatively close to a power line or to other metallic structure carrying AC current or it is bonded to another structure that is being affected by AC. This is different from the 120 Hz ripple left on pipes from single-phase cathodic protection rectifiers or the 360 Hz ripple left from three-phase rectifiers, which may present itself as an RMS AC voltage when referenced to the earth. A check of the voltage frequency usually can be used to rule out cathodic protection system ripple. If odd multiples of 60 Hz are present on the pipeline, this has likely come from coupling to a power line that has a component of harmonic distortion.