Corrosion is expensive. Across Europe, the degradation of metal structures generates billions of euros in costs every year — repairs, replacements and production downtime. Yet in most cases it is a predictable and preventable phenomenon, provided the right anti-corrosion system is applied at the right time.
This guide explains when an anti-corrosion treatment is required by law or by contract, how to select the correct system, and why working with a certified applicator makes the difference between a treatment that lasts and one that deteriorates within a few years.
What is an anti-corrosion treatment and why it is not “just a paint job”
An anti-corrosion treatment is a multi-stage system: surface preparation, primer application, intermediate coats and topcoat. Each stage must comply with precise technical specifications — thicknesses, recoating intervals, ambient application conditions — for the overall system to deliver the performance it was designed for.
The international reference standard is ISO 12944, which defines the classification of corrosive environments, surface preparation requirements and protective coating systems. Specifying an ISO 12944-compliant system is not a bureaucratic formality: it is the assurance that the treatment has been designed to last in that specific exposure environment.
Corrosivity categories: from C1 to CX
The first step of any anti-corrosion project is identifying the corrosivity category of the environment in which the structure will operate. ISO 12944 defines six main categories, plus three categories for submerged or buried structures.
C1 — Heated indoor environments with low humidity. Very low corrosivity, minimal requirements.
C2 — Rural areas with low pollution, unheated interiors. Low corrosivity.
C3 — Urban and industrial environments with moderate pollution, low-salinity coastal areas. The most common category for industrial and commercial buildings.
C4 — Industrial plants, coastal areas, chemical environments. High corrosivity, requiring thicker systems and higher-performance products.
C5 — Aggressive industrial environments with high humidity and salinity, chemical and petrochemical plants. Very high corrosivity, requiring the most demanding systems.
CX — Offshore structures and extreme environments. The most severe category, for energy and marine infrastructure.
The category determines the minimum system thickness, the type of products required and the expected design life — the period for which the system is designed to maintain its performance before requiring routine maintenance.
When is an anti-corrosion treatment mandatory
Metal structures subject to technical standards
Any steel structure intended for public use or regulated industrial contexts must be protected against corrosion in accordance with applicable standards. Across Europe, structural design codes require that steel structures be designed for long-term durability, which entails specifying an anti-corrosion system appropriate to the exposure environment.
For infrastructure such as bridges, viaducts and civil works, project specifications issued by public authorities and infrastructure owners define anti-corrosion system requirements in accordance with ISO 12944, including surface preparation grade, minimum thicknesses and required design life.
Industrial plants and the energy sector
Production facilities, tanks, pipelines and load-bearing structures in chemical, petrochemical and energy plants operate in environments classified C4, C5 or CX — categories that require high-performance anti-corrosion treatments as an essential condition for operational safety and regulatory compliance.
In these contexts, anti-corrosion treatment is not a choice but a project requirement, typically verified by third-party inspection bodies and documented in the plant’s technical file.
Renovations and changes of use
When an existing structure is renovated or its intended use changes, the structural design must assess the condition of the existing protective coating. If the original system no longer meets the requirements of the current exposure environment — because the use has changed or because the coating has deteriorated — a restoration treatment is required to bring the structure back into compliance with the applicable specifications.
In these cases, ISO 8501-2 applies, which defines preparation grades for steel surfaces that are already coated or partially rusted, as distinct from ISO 8501-1, which is used for new structures.
How to choose the right anti-corrosion system
The choice of system depends on three main variables: the corrosivity category of the environment, the design life required by the project, and the type of structure to be protected.
A system for a C3 environment with a medium design life is very different from one for a C5 environment with a very high design life. Products, thicknesses, number of coats and surface preparation requirements all change accordingly. In most cases, surface preparation involves abrasive blasting to Sa 2½ or Sa 3 in accordance with ISO 8501-1.
Surface preparation is the most critical phase of the entire process. According to SSPC and NACE guidelines, surface preparation is the single most important factor determining the durability of an anti-corrosion system — more so than the quality of the product applied or the film thickness. Investing in proper preparation is the most cost-effective decision in the long run.
Why work with a certified applicator
Correctly executing an anti-corrosion system requires expertise that goes well beyond product application. Controlling ambient conditions before and during application is critical to the success of the treatment. Application carried out outside the specified conditions can compromise the entire system’s performance, even when first-class products are used.
A certified applicator like FES Global Group manages the entire process with FROSIO- and NACE-qualified inspectors: from preliminary assessment and corrosivity category identification, through surface preparation in accordance with ISO 8501-1 and ISO 8501-2, to certified application with instrumental thickness control, and final technical documentation confirming the system’s compliance with project specifications.
That documentation is not a formality. It is an essential requirement for the validity of the system warranty and for reporting to project owners and construction managers.