Corrosion performance needs to be considered along with other design factors such as mechanical properties and weldability. The critical considerations for material selection are:
1) Lifetime cost including maintenance, monitoring, or replacement
2) Mechanical characteristics
3) Easy availability and logistics
4) Fabrication requirements
5) Forming joints by soldering or welding
6) Maintainability Surface Preparation
Preparing the surface of the metal prior to coating is an important requirement. Among the factors influencing the effectiveness of performance of coatings, surface cleanliness is probably the most significant. Any scale, grime, grease and rust must be completely removed before the application of a coating begins, to ensure the complete and strong adhesion of the film of the coating with the substrate. Barrier protection is lost if the adhesion is inadequate.
The cleaning techniques used include acid pickling or shot blasting. Acid pickling is used for metal that is to be coated by a galvanising process. For offshore structures and ships, blast cleaning is the prescribed cleaning method. For structural metals like steels and alloy steels, an abrasive cleaning method is also used for surface preparation. Selecting the Appropriate Protective Coating
For surfaces remaining in fully immersed conditions, a barrier coating system could be preferable, along with cathodic protection. Paint application is always considered as the first choice for corrosion protection, compared to metallic spray coating. Paint consists of a pigment, a binding medium and a solvent. The pigment, which forms the core of the coating, is made up of solid particles, which are kept well-dispersed by the solvent and the binder. Paints can be specifically formulated to ensure the essential properties necessary for the specific application, such as water resistance and scratch resistance. In order to minimize coating defects, multiple coats of paint are applied to the substrate. Before applying the first coat, the primer is applied to the substrate to improve adhesion.