Preferred solution, K12 – Appendix O Material technology and steel in marine environment

Abstract

The bridge design life is 100 years and this document discusses material selection and means of providing corrosion protection to limit the need for future inspections, maintenance, and replacements. The recommended solutions are summarised in the table below.

The most severe exposure conditions are in the splash zone and in this area carbon steel will be replaced by a corrosion resistant alloy, 25Cr DSS. Welding of carbon steel to 25Cr DSS is fully manageable provided properly qualified procedures and suitable materials are used.

High level cathodic protection (CP) calculations have been performed. The anode weight requirements vary dependent on the selected CP design life and extent of coating on the 25Cr DSS plates. Detailed calculations should be performed in next phase.

Corrosion allowances (CA) for the mooring chains have been evaluated based on standards and requirements included in the SVV design basis. Since the top chain is situated below the splash zone, the same CA as for the bottom chain is proposed (0.2 mm/year).

Recommendations for further work is included in a separate section at the end of the document