Home NI423 Corrosion protection of steel offshore units and installation This Guidance Note provides guidelines for the prevention and control of corrosion on steel structures, appurtenances and equipment of offshore units. Reference Title Date NI423 R01 Corrosion protection of steel offshore units and installation May 2006 check related documents: NR445 Rules for the classification of offshore units NR426 Construction survey of steel structures of offshore units and installations Check other Bureau Veritas rules and guidelines.