Isolation Joint Stray Currents – Experimental Testing and Modelling

Risks of stray current corrosion in pipelines with isolation joints have been investigated. The subsea pipelines in question have cathodic protection with sacrificial anodes and are separated electrically from the onshore part with monoblock isolation joints. The onshore part is an above ground installation without cathodic protection. It is, however, believed that the onshore installation has contact with sea trough electric grounding systems and quays. With the subsea pipelines at a potential of -1050 mV and the onshore steel structure and process equipment at its corrosion potential of around -600 to -650 mV, a voltage shift of 400 mV across the isolation joints is expected. This was also confirmed by measurements.

The risk of stray current corrosion, given the case described, have been investigated with experimental testing using a large scale experimental model of an isolation joint and a modelling software with polarisation curves as input.