Combining cathodic protection with aluminium coatings to reduce the external corrosion of hot risers

A new joint industry project has recently started to demonstrate the technical and financial benefits of the combined use of thermally sprayed aluminium (TSA) coatings and cathodic protection (CP) when applied to thermally cycled risers and hot hydrocarbon transportation pipelines.

Although TSA coatings are widely used to reduce the corrosion rate of offshore facilities, there are very few published data covering the simultaneous use of TSA coatings and CP when applied to subsea hot risers and hydrocarbon transportation pipelines. As a result, little consideration has been given to the interaction of TSA with anodes or impressed current CP systems in international standards (such as ISO 15589-2 and DNV-RP-B401) with the result that guidance is limited.

With many fields under development involving the installation of remote, deep-water facilities and the extraction of higher-temperature hydrocarbons, it is expected this project will generate significant benefits to the oil and gas sector including:

  • generation of environment-specific CP design data, providing increased confidence in the long-term reliability of TSA coatings in inaccessible, deep-water service
  • longer design life with reduced maintenance costs for facilities in remote locations
  • the opportunity to reduce significantly the anode mass on subsea structures.

The project work scope includes measurement of the effects of representative environmental conditions (oil temperatures up to 130°C) on TSA coating and anode behaviour when subject to both constant elevated temperature and thermal cycling. An important output of the project will include interpretation of the project results and implications for offshore structure CP design.