Metals and surface treatments

Uncontrolled corrosion is a recurrent problem with all applications involving metals, it may lead to a reduction in the performance and lifetime of the installation.
Cable trays are mainly exposed to atmospheric corrosion. The environment in which the cable trays are installed is therefore the main criterion in the choice of surface treatment or the type of steel.

Atmospheric corrosion affecting metals involves a chemical reaction between the iron found in steel and dioxygen in air or water (condensed moisture, rain or spray). The reaction produces the chemical compound Fe(OH)3, more commonly known as rust.

GALVANIC CORROSION

Corrosion is the result of an electrochemical phenomenon due to the potential difference between different metals, or between a metal and the impurities it contains, when they are in electrical contact. It is necessary to take into account this phenomenon when selecting the supports, fixings and connections.  The surface treatment of each component must be compatible: Wire cable trays   Accessories EZ/PG GC 304 L 316 L => => => => EZ/GS GC/DC 316 L 316 L

COATED STEELS

Galvanic protection of steel is a sacrificial process.  Zinc, in contact with the oxidising agent, is converted into zinc hydroxycarbonate (white) so protecting the steel.

	PG/GS: Continuous galvanisation before manufacture using the Sendzimir process EN 10244-2: PG standard (wire) EN 10327: GS standard (accessories)
Before manufacture, a coating of zinc is deposited by continuous immersion on the steel sheets or wires. The appearance of the components is now smooth and grey.

Electrogalvanising after manufacture EN 12329 standard

The cable tray, manufactured using untreated steel wire, is pickled and then immersed in an electrolyte containing zinc. Zinc is then deposited on it by passing an electric current. A smooth bluish-grey, fairly glossy appearance is obtained to a greater or lesser extent depending on the pH value of the electrolytic bath used. The colour and level of gloss have no negative or positive effect on the corrosion resistance of the coating.

Ongoing protection

When a wire cable tray is cut, the fact that a wire has been cut does not affect the level of protection.The jaws of the bolt cutter drags a layer of zinc across the cut end and forms a protective layer.

Hot dipped galvanised after manufacture EN ISO 14 61 standard

The cable trays or accessories, manufactured from untreated steel sheet or wire, are degreased and pickled before being immersed in a bath of molten zinc. The entire product is therefore covered with a thick layer of zinc. A light grey, slightly rough appearance is obtained. NOTE: Any white marks due to the formation of zinc hydroxycarbonate which might appear on the surface have no influence on the corrosion resistance. This is in fact the very principle on which galvanic protection is based.

	Geomet®
Geomet® is a treatment based on zinc and aluminium. As it does not contain any chromium VI (hexavalent), it complies with the RoHS Directive. Offering protection equivalent to GC, it is used for small accessories and fixings which are difficult to hot dip galvanise.

Epoxy
Resin-based paint is applied to the cable tray using an electrostatic powder and then cured in an oven. The entire range of RAL colours can be obtained. Mainly used for aesthetic reasons and to help identify cable routes, it offers very good corrosion resistance.

STAINLESS STEELS

In particularly harsh environments, selecting the right type of steel is more important than the coating. CABLOFIL uses two austenitic stainless steels, 304 L and 316 L, for their high level of corrosion resistance. This is partly the result of their very low carbon levels ("L" stands for "low carbon").

Figures for salt spray tests, baseline 100: EZ

	Stainless steel 304 L EN 10088-2 standard AISI 304L – X2CrNi18.09 – 1.4307
Offers good corrosion resistance against soft water, normal environments and food products (except mustard and white wine).

	Stainless steel 316 L EN 10088-2 standard AISI 316L – X2CrNiMo17.12.2 – 1.4404
Since it contains molybdenum, stainless steel 316L is able to resist intergranular corrosion. This makes it particularly suitable for the chemical and food industries, the nitrate explosives industry and environments containing halogen (fluorine and chlorine).

Decontamination of stainless steels

There are two key stages for prolonging the service life of the product and, by implication, the installation:
- Pickling in acid after degreasing eliminates pollutants.
- Passivation artificially creates a film of chromium oxide on the surface of the steel.
Corrosion-resistance tests involving salt spray and S02 (sulphur dioxide) highlight the importance of these two processes.

Untreated	Pickled and passivated	Untreated	Pickled and passivated

Pickling and passivation give CABLOFIL's stainless steel a very light grey colour and a distinctly matt finish.
All CABLOFIL stainless steel products are pickled and passivated.