Choosing a suitable anti-corrosion system is a technical process that must meet the requirements of the international standard. NF EN ISO 12944 and French certification ACQPA.
Here is the step-by-step methodology for making this choice rigorously.
Step 1: Define the Corrosivity Category (Environment)
According to Part 2 of ISO 12944, you must first identify the environment in which the structure will be located. This is the most critical parameter.
Category | Corrosivity | Examples of environments (Exterior) | Examples of environments (Interior) |
C1 | Very weak | N/A | Heated buildings (offices, schools). |
C2 | Low | Rural atmospheres, low pollution. | Unheated warehouses, gymnasiums. |
C3 | Average | Urban or moderately industrial, seaside (low salinity). | Breweries, dairies, laundries. |
C4 | Élevée | Industrial areas, coastal areas (moderate salinity). | Chemical plants, swimming pools. |
C5 | Very high | Industrial areas (high humidity/aggressiveness), coastal/maritime areas. | Buildings with permanent condensation. |
CX | Extreme | Offshore, extreme industrial zones, humid tropical regions. | Extreme industrial zones. |
Note: There are also categories Im1 to Im4 for submerged structures (fresh water, sea water, soil).
Step 2: Define the Desired Durability (Lifespan)
The ISO 12944-1 standard defines “durability” as the expected time before the first major maintenance of the paintwork. Please note: This is not a legally mandated warranty period, but a technical planning concept.
- L (Low): 2 to 7 year-olds
- M (Medium): 7 to 15 year-olds
- H (High): 15 to 25 year-olds
- VH (Very High): > 25 years
-
Tip: For engineering structures or industrial sites that are difficult to access, the aim is systematically to H ou VH.
Step 3: The Role of the ACQPA
Once you have defined your need (for example: C4 High Durability), you must choose a paint system. This is where ACQPA comes in.
ACQPA certifies complete systems (primer + intermediate + topcoat) offered by paint manufacturers. Choosing an ACQPA-certified system guarantees that:
- The system has been tested in the laboratory according to strict protocols.
- The performance corresponds well to the displayed corrosivity class.
- The industrial reproducibility of the products is controlled.
Step 4: Select the Paint System
An anti-corrosion system is generally composed of several layers, each with a specific role.
To choose the right system, you should consult the ACQPA certified system fact sheets based on your previous criteria.
Here are the common typologies:
- Surface preparation
This is the foundation of the system. ISO 12944-4 and ACQPA standards generally require abrasive blasting (sandblasting/shot blasting) to the degree Sat. 2.5 ou Sat. 3.
- If sandblasting is impossible (on-site maintenance), specific systems for mechanically prepared surfaces (St2 or St3) exist but are less efficient.
- Primary Layer Selection (The Key Layer)
- Zinc-rich primary: Cathodic protection (sacrificial). Ideal for C4, C5, CX. Very high performance but requires perfect sandblasting (Sa 2.5).
- Epoxy primer (non-zinc): Barrier effect protection. More tolerant, often used in C3 or C4.
- Total thickness (NDFT)
ISO 12944-5 defines minimum thicknesses. The more aggressive the environment, the greater the required thickness.
- Example C3 High: approximately 160 to 200 µm.
- Example C5 High: approximately 280 to 320 µm (often 3 layers).
Summary: How to read an ACQPA certification?
When you receive a technical proposal from a manufacturer, check the ACQPA certification number. It is often in the form of a code that validates the intended use.
Example of a selection process:
- My project : A metal container by the sea.
- ISO 12944 analysis: Seaside = Category C5 (or C4 if > 3km from the coast). Let's say C5.
- Durability: I don't want to repaint for another 20 years. High (H).
- ACQPA search: I am looking for a certified system for C5-H.
- Typical example result:
- Preparation: Sat 2.5
- Layer 1: Zinc Epoxy Primer (60 µm)
- Layer 2: Epoxy Intermediate (140 µm)
- Layer 3: Polyurethane finish (for UV resistance) (60 µm)
- Total thickness: 260 µm.
Important points to be aware of
- Polyurethane finish: Mandatory if the structure is exposed to sunlight (UV). Epoxies chalk (whiten) in the sun.
- Quality Control : A good system is worthless if it is poorly implemented.
Schedule inspections:
- Sheet metal preparation
- Dry thickness measurement between layers
- Surface temperature measurement
- Ambient temperature measurement
- Humidity level measurement
- Dew point measurement
