The corrosion protection in shipbuilding is performed in different methods. But all of them are just variations of one of the following methods: alloying, inhibitory protection and protective coatings.
In order to improve steel corrosion protection chrome, nickel, titanium, molybdenum and some other elements. But sufficient effectiveness of stainless steel in sea water can be provided only in case if it contains more that 18% of alloying elements that significantly increases the steel cost. This is why alloying didn’t gained wide spread in shipbuilding.
Inhibitors, or anticorrodant materials, are such compounds that when adding in small amounts to aggressive environment inhibit or prevent corrosion.
Inhibitory protection is used only in close rooms. This is why this type of protection can find application mainly at oil tank barges for corrosion prevention of bulk oil space inner surfaces. In this case inhibitors can be injected both in petrolium products and in incoming ballast water. Usually inhibitors are injected into a mortar that is used for tank washing after cargo or ballast extraction.
The simplest corrosion protection is the application of protective film to metal surface. Depending on the type of protective film coatings can be varnish-and-paint, metallic and non-metallic.
Varnish-and-paint waterproof sealants for crafts are widely used in shipbuilding, thanks to its low cost and the simplicity of application, also a satisfying effectiveness in case of unsatisfactory performance of all the preparatory and painting works. Applied in thin layer to the surface, varnish-and-paint sealants after drying out transform into thick elastic film that not only separates the metal from the environment, but also prevents electric couples formation on metal surface. Waterproofing spray for crafts is also one of the varnish-and-paint waterproof sealants. It is simple to apply and it forms a reliable protective layer that protects metal from corrosion.
Metallic coatings are used significantly more rare. Different metals can be used as coatings: copper, zinc, stannary, nickel, chrome and others. In shipbuilding galvanizing is used more widely. The most part of ship system pipe-lines and some deck fittings are subjected to this method.
Non-metallic coatings have low cost. In many cases its application gives significant cost cutting. Compartitions of double bottom and peaks are usually covered with cement aqueous solution, and places difficult of access are filled with concrete. It is more reasonably to use cement and concrete for coating bilge, waterways and other places where water accumulates.