Structural steelwork is where coating economics are most visible: large surface areas, accessible inspection, and a strong temptation to specify by price per litre. The specification should instead be set by the corrosivity category at the actual location, the accessibility of the structure for future maintenance, and the required interval between repaints.
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Bridges and plant steelwork
Atmospheric corrosion protection for fabricated steelwork from C3 inland exposure to C5 coastal and industrial.
Bridges and plant steelwork — Atmospheric corrosion protection for fabricated steelwork from C3 inland exposure to C5 coastal and industrial. Service environment: ISO 12944 C3 to C5-I / C5-M; typical design life: 15–25 years. The table below lists the recommended coating build-up and links to the matching product categories and selectable products.
CorrosivityISO 12944 C3 to C5-I / C5-M
Typical service life15–25 years
Recommended coating system
| Layer | Type & DFT | Product examples |
|---|---|---|
| Primer | Zinc-rich epoxy, 60–80 µm, or zinc-free for C3 | Zinc-rich primer |
| Intermediate | MIO epoxy, 80–120 µm | MIO epoxy |
| Topcoat | Aliphatic polyurethane, 60–80 µm | PU topcoat |
| Total | 160–240 µm across C3 to C5 | According to ISO 12944-5 |
Application critical points
- Hard-to-reach areas — box sections, the back of stiffeners, connection plates — should be specified to a higher standard, because they will never be repainted in service.
- For C3 and C4 inland exposure, a correctly specified zinc-free system can be a better whole-life choice than a zinc primer that is applied under pressure of cost cutting.
- Shop priming and the maximum exposure time before the site coat must be planned together; steelwork often waits in the open for months.
Related product categories
Related products from the brands used in this scenario
Interdur 8803DIMETCOTE 3WEPOFEND ZINC 60Intercure 384PHENGUARD 935EPOFEND MIO 30InterH2O 699PHENGUARD 940
Related brands & products
Frequently asked questions
Which coating system is recommended for Bridges and plant steelwork?
The recommended build-up is: Primer; Intermediate; Topcoat; Total.
What is the service environment for Bridges and plant steelwork?
Service environment: ISO 12944 C3 to C5-I / C5-M; typical design life: 15–25 years.
Which brands are covered by this scenario?
Brands covered by this scenario: AkzoNobel International, PPG, KANSAI, 3 TREE.
Articles are compiled by RichTech from publicly available manufacturer materials and field practice, for selection reference only; the latest official technical data sheets (TDS) prevail.
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