Fighting corrosion requires a strict strategy
Steel assets face corrosive conditions that are defined by the environment that they are in during construction and in service. The combination of weather, salinity and pollution define the corrosivity of the environment.
A protective coating system offers anticorrosive power by using active galvanic pigments such as zinc, inhibitive pigments such as zinc phosphate, or by using the barrier principle, preventing moisture penetration (water or water vapour) through the coating film. This barrier effect can be enhanced using special pigments such as micaceous iron oxide (sometimes abbreviated to mio or miox) or glassflake.
General Steel constructions- C2 - low corrosivity according to ISO 12944
- C3 - medium corrosivity according to ISO 12944
- C4 - high corrosivity according to ISO 12944
- C5-I very high (industrial) corrosivity according to ISO 12944. *
- C5-M very high (marine) corrosivity according to ISO 12944. *
* in the 2018 update of the standard these categories have been merged
More about selecting coating systems for general steel constructions including off-shore (CX) in our Guide to ISO 12944.
The use of an asset determines which maintenance strategy is applicable and feasible. Read more about planning a maintenance strategy here.
Different type of assets have different requirements during application of the coating or expected physical wear and tear that may affect the coating selection.
Coating systems are generally built up in multiple coats of variying dry film thickness (DFT). The first coat on the suitably prepared and cleaned substrate is called the primer. The intermediate, mid-coat or build-coat layer(s) are used ot add film thickness to the system which provides the barrier effect mentioned earlier. A final topcoat or finish adds the colour, its gloss retention in exposure to UV light form the sun can be a decision making factor when high outdoor durability and weathering resistance is importent.
Various factors can determine the choice of a system and in order to come to a decision, it must be clear which one has the highest priority. The combined technical requirements related to the nature of the project (expected application conditions, in-service temperature and environment, budget) are part of the decision to choose between the different generic chemistries, or binder type, that are available: acrylic, alkyd, epoxy, silicone, silicate, poly-siloxane, poly-urethane and so on. Local environmental regulations may push a decision to high solid, solvent free or water based options.
Important properties of a coating system are related to adhesion: its primer should adhere firmly to the substrate and subsequent coating layers should have appropriate 'intercoat' adhesion between the applied paint layers. Furthermore, the system must be resistant to possible corrosive polution or chemical agents (splash and spillage) and expected mechanical impact for which cohesive strength and abrasion resistance play a role.
