The ways in which a metal hull may be protected

Shipwrecks and Salvage‎ > ‎4. Marine Protection‎ > 

Identify the ways in which a metal hull may be protected including:
– corrosion resistant metals
– development of surface alloys
– new paints

  • Marine environments accelerate the corrosion of iron or steel due to the presence of electrolytes, which promote galvanic action.
  • The steel hulls of ships may be protected by:
    • Corrosion resistant metals.
      • Stainless steel effectively resists corrosion.
      • A passive film of chromium (III) oxide forms on stainless steels and prevents further corrosion.
      • The cost of stainless steel makes its use as ship hulls prohibitively expensive.
    • Surface alloys.
      • It is possible to form a stainless steel like surface on ordinary steel by bombarding it with ions of chromium and nickel.
      • These metal ions are formed in a high temperature gaseous discharge and are directed at the surface of ordinary steel where they become embedded as atoms and so form a surface alloy.
      • The bulk of steel below the surface remains unaltered.
      • The surface alloy resists corrosion almost as well as solid stainless steel.
    • New paints.
      • Polymer-based paints have been developed that are particularly effective in protecting against rust.
      • The polymer cures in air to form a film that is quite impervious to oxygen and water.
      • Additives in the paint react with surface atoms in the steel to form a layer of very insoluble substance called pyroaurite.
      • This ionic layer is tightly bonded to the steel surface and extends well into the polymer layer, effectively protecting the migration of ions from one place on the steel surface to another, and thus preventing rusting.