This document specifies the requirements and recommendations for cathodic protection systems applied to the internal surfaces of metallic tanks, structures, equipment, and piping containing raw or treated seawater or brackish waters, to provide an efficient protection from corrosion. Cathodic protection inside fresh water systems is excluded from this document. This is covered by EN 12499. NOTE EN 12499 covers internal cathodic protection for any kind of waters, including general aspects for seawater; but excluding industrial cooling water systems. This document specifically details applications in seawater and brackish waters.