What corrosion protection is
Corrosion protection of steel structures is a set of measures that slow down the deterioration of carbon and low-alloy steel caused by moisture, oxygen, salts and industrial gases. The most common method is a paint system: several coats, each of which has its own job. Besides painting, hot-dip galvanising, thermal spraying of zinc and aluminium and cathodic protection are used; these solutions are often combined with paint systems.
Online system selector. Answer a few questions and we will show the ISO 12944 environment category, the type of coating system and the materials in our catalogue. Select a corrosion protection system →
A coating protects steel in three ways, and in a good system they complement one another.
- Barrier. A dense film holds back water, oxygen and salts. The thicker and more continuous the film, the longer the path the aggressive environment has to travel to reach the metal.
- Inhibition. Anti-corrosive pigments in the primer slow down corrosion processes at the steel surface.
- Sacrificial action. The zinc in zinc-rich primers corrodes instead of the steel and protects it even where the coating has minor damage.
How a coating system is selected
A system is chosen on the basis of four groups of input data: the service environment, the required durability, the condition of the surface and the method of preparing it, and the application conditions. The international basis is the ISO 12944 series of standards on the corrosion protection of steel structures by protective paint systems. The key parts of the series in their current editions are listed below.
| Part | Subject |
|---|---|
| ISO 12944-1:2017 | General introduction, durability ranges of systems |
| ISO 12944-2:2017 | Classification of environments: corrosivity categories for atmosphere, water and soil |
| ISO 12944-3:2017 | Design considerations that make protection easier |
| ISO 12944-4:2017 | Types of surface and surface preparation |
| ISO 12944-5:2019 | Protective paint systems |
| ISO 12944-6:2018 | Laboratory performance test methods for systems |
| ISO 12944-7:2017 | Execution and supervision of paint work |
| ISO 12944-8:2017 | Development of specifications for new work and maintenance |
| ISO 12944-9:2018 | Systems and test methods for offshore and related structures |
1. Service environment: categories to ISO 12944-2
ISO 12944-2:2017 divides atmospheres into six corrosivity categories. The category is determined from the mass or thickness loss of standard low-carbon steel specimens after the first year of exposure; the category limits correspond to ISO 9223. Where no measurements are available, the descriptions of typical environments are used as a guide.
| Category | Corrosivity | Steel thickness loss in the first year, µm | Exterior examples | Interior examples |
|---|---|---|---|---|
| C1 | very low | up to 1.3 | — | heated buildings with clean atmospheres: offices, shops, schools, hotels |
| C2 | low | over 1.3 up to 25 | atmospheres with a low level of pollution, mostly rural areas | unheated buildings where condensation may occur: warehouses, sports halls |
| C3 | medium | over 25 up to 50 | urban and industrial atmospheres with moderate sulphur dioxide pollution; coastal areas with low salinity | production rooms with high humidity and some air pollution: food-processing plants, laundries, breweries, dairies |
| C4 | high | over 50 up to 80 | industrial areas and coastal areas with moderate salinity | chemical plants, swimming pools, coastal shipyards |
| C5 | very high | over 80 up to 200 | industrial areas with high humidity and aggressive atmospheres; coastal areas with high salinity | buildings and areas with almost permanent condensation and high pollution |
| CX | extreme | over 200 up to 700 | offshore areas with high salinity; industrial areas with extreme humidity and aggressive atmospheres; subtropical and tropical atmospheres | industrial areas with extreme humidity and aggressive atmospheres |
In the 2017 edition the former categories C5-I and C5-M were merged into a single category, C5, and category CX and immersion category Im4 were added. If a manufacturer’s documents refer to C5-I or C5-M, they are based on the previous edition of the standard.
For structures in water and soil the standard introduces separate categories: Im1 — fresh water (river installations, hydroelectric power plants), Im2 — sea or brackish water without cathodic protection, Im3 — soil (buried tanks, steel piles, pipes), Im4 — sea or brackish water with cathodic protection. In Uzbekistan, Im1 and Im3 matter most in practice: canals and hydraulic structures, buried tanks and pipelines.
The category is determined for the specific location, not for the region as a whole. The dry climate of most of the country does not in itself guarantee a mild environment: local factors decide — emissions from neighbouring plants, splashes and spills of process media, constant condensation in unheated buildings, saline soils for buried structures, salt dust in the Aral Sea region. Designs prepared to CIS standards use their own classification — degrees of aggressive exposure; there is no direct conversion into ISO 12944-2 categories, and the comparison is made by the designer.
2. Required durability: ISO 12944-1
ISO 12944-1:2017 defines four durability ranges for a coating system:
- L (low) — up to 7 years;
- M (medium) — 7 to 15 years;
- H (high) — 15 to 25 years;
- VH (very high) — more than 25 years.
Durability is the expected life of the system until the first major maintenance of the coating, not a guarantee period. The higher the corrosivity category and the required durability, the more coats and the greater the total thickness of the system, and the stricter the surface preparation requirements.
3. Surface preparation: ISO 12944-4 and ISO 8501-1
No material performs better than the surface preparation underneath it. ISO 12944-4:2017 describes surface types and preparation methods, while the preparation grades are defined by the reference photographs of ISO 8501-1:2007:
- initial condition of the steel — rust grades A, B, C, D: from a surface covered with adherent mill scale and little rust to a surface completely rusted with visible pitting;
- abrasive blast cleaning — Sa 1 (light), Sa 2 (thorough), Sa 2½ (very thorough), Sa 3 (to visually clean steel);
- hand and power tool cleaning — St 2 (thorough) and St 3 (very thorough);
- flame cleaning — Fl.
For zinc-rich primers and most high-performance systems, technical data sheets require Sa 2½; surface-tolerant epoxy mastics accept St 2 – St 3 where blast cleaning is impossible, usually in maintenance work. The visual preparation grade is not the only criterion: surface profile is assessed to ISO 8503, residual dust and soluble salts by the methods of the ISO 8502 series, the preparation of welds and edges is specified to ISO 8501-3, and water jetting to ISO 8501-4. Documentation prepared to CIS standards specifies surface preparation to GOST 9.402, by degree of cleaning from oxides.
4. System logic: primer — intermediate coat — topcoat
- The primer provides adhesion to the steel and active protection: zinc-rich (sacrificial action) or epoxy.
- The intermediate coat builds up barrier thickness. Most often this is a high-build epoxy, frequently with micaceous iron oxide (MIO), whose lamellar flakes lengthen the path of moisture to the metal.
- The topcoat protects the system from UV and weathering and provides colour and gloss: an aliphatic polyurethane or a polysiloxane. Epoxy coats chalk in sunlight, so outdoors they are never left without a topcoat.
ISO 12944-5:2019 describes the binder types and gives example systems for different corrosivity categories and durability ranges, with the number of coats and the nominal dry film thickness. Systems are qualified in the laboratory to ISO 12944-6:2018, and for offshore structures and categories CX and Im4 to ISO 12944-9:2018. Manufacturers also offer shortened schemes, for example two coats with a high-build polysiloxane topcoat instead of three, but such a scheme must be proven for the specific environment and service life.
The main rule: all coats of the system come from one manufacturer and from one compatibility list. A system assembled from different brands “on price” is a common cause of intercoat delamination.
Sections of the guide
- Zinc-rich primers — zinc silicate and epoxy zinc primers for highly corrosive environments.
- Cold galvanising — one-pack compounds with a high zinc content for stand-alone protection of steel and repair of galvanising.
- Epoxy primers, intermediate coats and mastics — the backbone of barrier protection, plus repair mastics for minimal surface preparation.
- Polyurethane and polysiloxane topcoats — the weather-resistant top layer of the system.
- Coatings for tanks and pipelines — internal linings for crude oil, petroleum products, chemicals and water.
- Heat-resistant coatings — hot surfaces and protection against corrosion under insulation.
- Chemical protection — vinyl ester linings and rubber lining of equipment for acids, alkalis and oxidisers.
Common mistakes in choosing corrosion protection
- The material is chosen without a corrosivity category or required durability — “by analogy” with another project.
- Saving on surface preparation while using expensive materials: a primer applied over mill scale, dust and salts delaminates together with the whole system.
- A system assembled from different manufacturers’ materials without confirmed compatibility.
- An epoxy used as an exterior topcoat — the surface chalks and fades.
- Painting without regard to the season: in hot weather the pot life shortens and dry spray appears; in cold weather and with dew the material does not cure properly.
- Acceptance “by eye” — without checking the surface preparation and the dry film thickness.
Materials from leading manufacturers
The guide covers anti-corrosion materials from major manufacturers. Detailed lists are given on the subsection pages; below are typical examples for each area.
- Interzinc 52 — International (AkzoNobel) — epoxy zinc primer for aggressive environments.
- Resist 86 — Jotun — zinc ethyl silicate primer, heat-resistant up to 540 °C.
- Jotamastic 90 — Jotun — epoxy mastic for maintenance painting over minimal surface preparation.
- Macropoxy EG-1 Plus — Sherwin-Williams — epoxy primer and intermediate coat with micaceous iron oxide.
- PPG SIGMADUR 550 — PPG — aliphatic acrylic polyurethane topcoat.
- Carboxane 2000 — Carboline — isocyanate-free polysiloxane topcoat.
- Tankguard Storage — Jotun — tank lining for crude oil, petroleum products and chemicals.
- PPG HI-TEMP 1027 — PPG — coating against corrosion under insulation, continuous service up to 650 °C.
- ZINCTECT 1500 — Kansai Paint — inorganic zinc silicate primer.
The properties on the material cards are taken from the manufacturers’ product pages and technical data sheets; each card gives a reference to the source.
How to request a system selection
To get an accurate proposal first time, please send us:
- what needs protecting: a frame, a pipe rack, a tank (external or internal), a pipeline, equipment; new construction or maintenance;
- conditions: indoors or outdoors, neighbouring plants and emissions, contact with water, product or soil, the operating temperature of the surface, whether there is thermal insulation;
- project requirements: the corrosivity category and durability to ISO 12944 or the degree of aggressive exposure to CIS standards, specified brands and permitted substitutes;
- surface condition: new steel (with mill scale or shop primer), rusted, or with an old coating; whether abrasive blast cleaning is possible;
- where the painting will be done — in the shop or on site — and at what time of year;
- the area to be painted or a steelwork schedule, colours, delivery dates;
- special requirements: contact with drinking water or food, aviation fuel, a hazardous area.
Based on this information, we will propose 1–3 system options from different manufacturers, explain the differences between them and obtain the current technical data sheets from the manufacturers.
About supply
We supply corrosion protection materials across Uzbekistan and to neighbouring Central Asian countries: we help check the project requirements, obtain technical documentation from the manufacturer and put together a complete system — primer, intermediate coat, topcoat and thinners. We select and calculate the protection scheme for your project and, where needed, organise painting through partner contractors with the necessary experience and qualifications.
Frequently asked questions
Can a system be chosen without a design?
As a preliminary choice, yes, if the environment, the required service life and the painting conditions are known. The final system with coat thicknesses is fixed by the design or by a specification agreed with the materials manufacturer.
Which is better: hot-dip galvanising or painting?
They are different tools. Galvanising suits parts that fit into the bath and needs no painting on site; a paint system is not limited by size or colour and is easier to repair. The two are often combined: a paint system is applied over galvanising, which requires special preparation of the zinc surface and a suitable primer.
Why not simply take a “thicker” system?
Extra thickness is not always beneficial: every material has a maximum coat thickness, above which cracking, blistering and solvent retention can occur. The system is selected for the environment and the service life, not with a thickness margin.
Does VH durability mean a 25-year guarantee?
No. Under ISO 12944-1, durability is a guide for planning maintenance, expressed as a range of years, not a guarantee period. A guarantee, if offered, is arranged separately.
The standards that apply to anti-corrosion work — ISO 12944 and ISO 8501–8504, NORSOK, AMPP/SSPC, GOST and SP, Uzbek codes and quality control — are explained in Anti-corrosion standards.
Need a corrosion protection system selected or a supply quotation? Call us or message us on WhatsApp/Telegram: +998 94 094 52 27.