As discussed in the previous article, among the metallic materials most commonly used in classified areas with a risk of explosive atmosphere formation are low-copper aluminum alloys and low-carbon austenitic stainless steels, primarily AISI 316L.

One potential critical issue for installations using such devices is the marine environment, where salt dissociates into chloride ions and water becomes an effective electrical conductor. Corrosion is, in fact, an electrochemical phenomenon.

The presence of chlorides can trigger pitting corrosion [1], which is why protective coatings, such as specific paint systems, are required to safeguard the metal against corrosion.

For devices intended for use in classified Zones with a risk of explosive atmosphere formation, the general standard EN/IEC 60079-0 establishes several requirements for paint layers. Paints, being non-metallic materials, can lead to the accumulation of electrostatic charges.

The requirements differ depending on whether the potentially explosive atmosphere is due to gases or dusts, since dusts are subject to brush discharge phenomena [2].

The primary strategy for mitigating electrostatic charge hazards consists in applying an antistatic coating, defined by the standard as a coating with a surface resistivity < 10^9 Ω [3].

If this requirement cannot be met, and the equipment belongs to Groups I or II, it is possible to limit the coating thickness to 0.2 mm. In the case of potentially explosive atmospheres due to dusts (Group III equipment), the risk of brush discharges renders this strategy ineffective.

For fixed installations, it is possible to mark the equipment with an “X”, potentially accompanied by a specific warning plate, and to include instructions in the user manual that guide the operator in eliminating the risk of electrostatic discharges.

Cortem’s coating, in the standard RAL 7035 colour, meets antistatic requirements while ensuring corrosion resistance for a C4 environment with high durability H according to ISO 12944-6

Regarding corrosion resistance of coatings, the normative reference that has become widely adopted in recent years is ISO 12944. This standard describes, through its various sections, how to classify the environment in relation to corrosion risk, how to prepare the surface to be coated, the coating systems, and finally the selection of coating systems [4].

Originally developed for painted steel structures, it has also become a useful reference for other metals where it can provide valuable guidance.

Over time, coating systems have also become a subject of interest both for their antistatic properties and for their corrosion resistance.

Today, polyester-based powder coatings provide high corrosion resistance even in harsh and extreme ambient temperature conditions. Their application process—and, of course, their formulation—is of great importance.

[1] form of localized galvanic corrosion

[2] the discharge does not originate from a precise point (as in the case of a spark discharge), but spreads over an area, producing small luminous filaments similar to hairs or bristles

[3] measurement performed according to the procedure in IEC 60079-0[4] CEI 31-108 GB.3.1