The expansion of high-voltage alternating current (HVAC) infrastructure across the UK has introduced significant challenges for the integrity of buried steel pipelines. This paper presents a detailed engineering case study addressing AC interference risks arising from the installation of a new 400kV HVAC overhead powerline.

The investigation included comprehensive risk assessments, soil resistivity surveys, cathodic protection (CP) system analysis, and the installation of zinc ribbon earthing to mitigate AC-induced corrosion. Post-energisation monitoring revealed elevated AC current densities and voltages at several locations, exceeding the 30 A/m² threshold defined in BS EN ISO 18086, highlighting the limitations of predictive modelling tools and the need for empirical validation.

As a direct outcome of this work, UKOPA guidance was developed to support pipeline operators in managing AC interaction risks. This includes:
• A structured risk assessment framework for identifying high-risk pipelines.
• A field work instruction for accurate measurement of AC voltage and current density.
• Recommendations for remote monitoring using electrical resistance (ER) probes.

The guidance has been disseminated across the UK pipeline industry and was formally presented at the IGEM/TD/1 Edition 6 panel, where it informed updated recommendations. The project also initiated collaboration with the safety regulators to promote joint forums between electricity and pipeline operators.

This case study underscores the importance of early engagement with infrastructure developers, the need for improved modelling methodologies, and the value of industry-wide collaboration to address AC interference risks in the context of increasing electrification and Net Zero targets.