La corrosión en pintura, categorías de corrosividad

Paint corrosion  is one of the main problems that can be found in protecting and preparing a metal surface. Corrosion can be defined as the phenomenon of natural deterioration of materials due to their interaction with the environment, caused either by chemical or mechanical attack or by an electrochemical reaction.

Thus, all metal surfaces that are exposed to the atmosphere, or that are under water or underground, are at risk of corrosion and therefore require extra protection against corrosion damage.

The following post delves into the types of corrosion that exist, the different categories of corrosiveness, anti-corrosion paints and the essential painting systems to prevent metal corrosion.

Why does paint corrosion occur?

Firstly, it is important to differentiate between oxidation (rust) and corrosion. Oxidation is the process prior to corrosion that is caused by the oxygen attacking certain material. Corrosion, however, is the consequence of this attack, giving rise to deterioration and wear in the body of the metallic material.

When the metal comes into contact with oxygen and humidity, a  complex electrochemical phenomenon takes place which will be the germ of corrosion. In addition to moisture, there are other corrosive agents, such as:

  • High temperatures.
  • Environmental salinity due to proximity to the sea.
  • Industrial pollution.
Tubería con corrosión

Types of corrosion in metals

In industrial paint there are different types of corrosion that will vary depending on the environmental conditions and on the characteristics of the material itself:

Atmospheric corrosion

It is a type of corrosion that develops evenly over the entire surface of the material. It occurs mainly due to the corrosive agents that are present in the atmosphere such as oxygen, carbon dioxide, water vapour, sulphur and chlorine compounds.

Ejemplo corrosión atmosférica

Galvanic corrosion

Galvanic corrosion is a very usual type of corrosion, which occurs when two materials of different potential are electrically joined in contact with an electrolyte such as salt water. Under certain circumstances, the galvanic corrosion reaction rate can be very high, so it is advisable to solve it as soon as possible.

Ejemplo corrosión galvánica

Pitting corrosion

Pitting corrosion is a generalised attack on the entire metal surface, and is accelerated by the presence of chlorides. It is a very dangerous type of corrosion, especially if it occurs in industrial tanks or silos containing liquids, as there is a risk that they may get pierced.

Ejemplo de corrosión por picadura

Turbulence corrosion

Turbulent corrosion takes place mainly inside tubes or pipes, due to the flow of liquids successively removing the layers of rust from their surface.

Ejemplo de corrosión por turbulencias

UNE EN ISO 12944 Standard and the classification of corrosive environments

International standards are used with the following criteria to determine and classify corrosive environments and resistance in painting systems. The standard defining, assessing and limiting these parameters is the UNE EN ISO 12944 standard, which focuses on supports such as:

  • Uncoated steel
  • Hot dip galvanising
  • Zinc coated steel with thermal spraying.

This standard refers to different corrosive environment categories, divided into 2 groups:

  • On the one hand there are corrosiveness categories for atmospheric environments.
  • On the other hand, corrosiveness categories for underwater or underground structures.

Corrosiveness Categories for Atmospheric Environments

The categories in this section include:

  • Category C1,with steel thickness losses of 1.3 microns. This category is mainly aimed at assessments of heated buildings with clean atmospheres, such as offices, shops, schools or hotels.
  • Category C2,  with steel thickness losses of 1.3 and up to 25 microns. Category defined for assessing atmospheres with low pollution levels, or unheated buildings where condensation may occur, e.g., warehouses, sports halls, etc.
  • Category C3,for steel thickness losses of 25 and up to 50 microns. This category is intended for assessing urban and industrial atmospheres, with moderate sulphur dioxide pollution. Also, for manufacturing halls with high humidity and some air pollution, e.g., food processing plant, laundries, brewery plants, dairy plants.
  • Category C4, for steel thickness losses of 50 and up to 80 microns. Defined to assess industrial and coastal areas with moderate salinity such as chemical plants, swimming pools, ships and shipyards.
  • Category C5, for steel thickness losses of 80 and up to 200 microns. Analysis and assessment of coastal and maritime areas with high salinity, and buildings or areas with near permanent condensation and high pollution.
  • Category CX, corrosiveness category applicable to extremely corrosive environments such as offshore areas, industrial areas with extreme humidity, and aggressive or tropical atmospheres.
Ejemplo de chapa con corrosión

Corrosiveness categories for underwater or underground structures.

  • Category IM1, for freshwater environments such as riverside installations or hydroelectric plants.
  • Category IM2, for seawater environments such as port areas with structures like containment gates, locks, docks, offshore structures.
  • Category IM3, for underground structures such as buried tanks, steel piles, steel pipes.
  • Category IM4, for structures at sea or brackish water, such as submerged structures with cathodic protection.

Furthermore,  standard UNE-EN ISO 12944 also specifies a paint system’s durability based on three time intervals:

  • Low (L): 2 to 5 years
  • Average (M): 5 to 15 years
  • High (H): over 15 years

Solutions to prevent paint corrosion

Anti-corrosion paint

As a first tip, we recommend that you use highly resistant and durable anti-corrosion products, which work as an efficient barrier against corrosion.

Pintura anticorrosiva

BESA has a wide range of products that adapt to different types of supports, corrosiveness categories and sectors. These include, among many other, machine tools, metallic structures, boilermaking, industrial vehicles.

Anti-corrosion paint systems – long-lasting, high-quality protection

From a functional and economic point of view, corrosion is a problem that has a direct impact on the possible replacement of parts or machines, and on their maintenance.

Consulta de sistema de pintado anticorrosivo

The correct choice of painting system and products will make them last longer and reduce costs.

BESA has different painting systems that have been designed to efficiently protect any type of metal surface against corrosion. These are certified with the UNE EN ISO 12944 Standard. These systems can vary depending on the products and the needs of each application. The following stand out:

1C Primer Systems

  • A-10. High Quality Industrial Synthetic System
    • System intended for painting metal structures, boilermaking, agricultural machinery and public works, lifting equipment, cranes, construction material, metal carpentry, industrial bodywork. It is a system where good resistance to oxidation and quality work is required at average cost.
    • System certified according to requirements of category C3 AVERAGE acc./UNE EN ISO 12944-2.
  • A-25 High Resistance Mixed System
    • System designed for painting metal structures, machinery in general, public works, industrial bodywork, etc. This system should be used when requiring high resistance to oxidation and quality work. The enamel has excellent hardness, elasticity, resistance to abrasion and aggressive agents.
    • System certified according to requirements of category C3 AVERAGE acc./UNE EN ISO 12944-2.

2C Primer Systems

  • B-10 Epoxy-Pur Industrial System
    • System designed for painting trailers and semi-trailers, truck tanks, concrete mixers, metallic structures, etc. F-294/2 can be applied on wet-on-wet finishes after 20-30 min. Alfapur 3748 Enamel has good elasticity, body, gloss and outdoor resistance.
    • System certified according to requirements of category C3 HIGH acc./UNE EN ISO 12944-2.
  • B-15 Low Voc Industrial Epoxy-Pur System
    • System designed for painting trailers and semi-trailers, truck tanks, concrete mixers, metallic structures, etc. The F-296/2, Ultra High Solids primer, formulated with epoxy resins and hardened with polyamide and its high anti-corrosion pigment content, provides the Painting System with excellent anti-corrosion protection.
    • System certified according to requirements of category C3 HIGH acc/UNE EN ISO 12944-2.
  • B-30 Epoxy System Zinc-Epoxy CG-Pur High Resistance Marine & Industrial Epoxy System
    • System designed for painting elements in the electrical sector (transformers), wind power, port cranes and any other element with High Resistance requirements.
    • System certified according to requirements of category C5 – I HIGH acc./UNE EN ISO 12944-2.

Direct systems

  • C-10, 1C Anti-corrosion single stage system:
    • System designed for painting in sectors such as agricultural machinery and public works, industrial vehicles, tanks, pipes, metallic structures, etc. (directly on the support). It has a semi-glossy appearance, is easily applied and spread, good filling power and fast drying.
    • System certified according to requirements of category C3 LOW acc./UNE EN ISO 12944-2.
  • C-20, UHS Pur 2C Anti-corrosion single stage system:
    • Ultra-High Solids System intended for painting machinery, silos, industrial vehicles, etc., with medium and high pressure equipment. Is elastic, has good body and resistant to oxidation. The support does not require any primer. It is also used as an alternative to conventional processes to reduce VOC emissions in installations.
    • System certified according to requirements of category C3 AVERAGE acc./UNE EN ISO 12944-2.
  • s, etc. (directamente sobre el soporte). Presenta un aspecto semibrillante, con fácil aplicación y buena extensibilidad, poder de relleno y rapidez de secado.
    • Sistema certificado según requisitos de la categoría C3 BAJA s/UNE EN ISO 12944-2.
  • C-20 Sistema Monocapa Anticorrosivo UHS Pur 2C:
    • Sistema Ultra Altos Sólidos orientado para el pintado de maquinaria, silos, vehículos industriales, etc., con equipos de media y alta presión. Presenta elasticidad y cuerpo y una buena resistencia a la oxidación sin necesidad de ser imprimado el soporte. También se emplea como alternativa a procesos convencionales para la disminución de emisiones VOC en Instalaciones.
    • Sistema certificado según requisitos de la categoría C3 MEDIO s/UNE EN ISO 12944-2.