CORROSION MAINTENANCE

Silicone corrosion coating Si-COAT 579CM applied to industrial steel

Si-COAT 579CM Silicone Corrosion Coating for Southern Africa

Si-COAT 579CM is a single component, moisture cure RTV silicone corrosion coating made by CSL Silicones. It protects weathered and rusted structural steel, tank exteriors, bridges, machinery, cladding and metal roofs above ground. CSL designed it for retrofit work on structures that stay in service. There is also a clear version, Si-COAT 581CM, for when you need to see the surface underneath. Technical Solution Supplies distributes CSL Silicones products across Southern Africa, including the DRC and the Seychelles.

It goes on as one coat over steel cleaned by hand tools, power tools or water jetting. As a result, you do not need abrasive blasting. For the most severe coastal and industrial sites, however, CSL pairs it with CSL 979 primer. That system passed ISO 12944-6:2018 testing for C5 High, as we explain further down.

Why a Silicone Corrosion Coating Without Blasting Matters

Most heavy duty coating systems expect abrasive blasting before the first coat. In a fabrication shop, that is routine. However, on a working plant, a live road structure or a tank in service, it often is not. Blasting needs containment, access and shutdowns. As a result, owners put the maintenance off until the rust is obvious.

Si-COAT 579CM suits that reality. A normal crew with wire brushes, grinders, needle guns or a water jetting unit can reach the surface standard it needs. In addition, they can do it inside a normal maintenance window. That turns deferred corrosion work into work that actually gets done. Our article on surface tolerant coating covers this in more detail.

Proven in the Florida Fence Test

Florida Power and Light ran a three year Florida Fence Test at Melbourne Beach, on the Atlantic coast. The test put 29 coating systems through sun, salt spray and weather. First, the lab rusted the steel panels. Then it cleaned them with hand tools only, to SSPC SP2. Si-COAT 579 was the only one coat system in the test. It went straight onto that rusted steel with no primer. Before exposure, the lab scribed every panel through to bare metal.

After 36 months, Si-COAT 579 showed no rust creep, bleed through, pinholes or loss of adhesion. By contrast, the three coat zinc, epoxy and polyurethane systems failed. They sat on steel blasted to white metal, yet showed heavy rust creep and adhesion failure. Because of that result, the utility coated its 85 metre fuel oil tank at West Palm Beach in 2002.

Field service backs this up. For example, in 2003 CSL coated about 24 km of process piping at a Florida power plant near the Atlantic coast. When CSL inspected it some 20 years later, the coating thickness measured the same as when it went on. Closer to home, our case studies cover a Free State fertiliser plant, a Johannesburg chlorine plant and a Durban harbour hopper. They also include a crude oil tank in Athens.

Key Properties of the Silicone Corrosion Coating

One coat. Si-COAT 579CM primes itself on most common substrates. So standard maintenance work needs no primer, intermediate coat or topcoat. Still, CSL recommends a quick field adhesion test first.

Stops rust creep. Besides the Florida Fence result, it also passed 3,000 hours of ASTM B117 salt fog.

UV stable. After 5,000 hours of accelerated weathering to ASTM G154, it showed no degradation. Its colour also changed by less than 1 delta E. That matters under Southern African sun, because organic topcoats chalk and fade.

Flexible. With 180% elongation at break, the film moves with the steel through heat cycles and vibration. As a result, it does not crack.

Bridges old coatings. CSL also tested it over an aged coating system. The old coating cracked in bend and impact tests. However, the Si-COAT layer on top bridged the cracks without damage. That suits maintenance work, where sound old paint stays on.

Tough and washable. It passes direct impact and mandrel bend tests. In addition, it handles high pressure water washing up to 150 bar, so it suits plants with routine washdowns.

Chemical exposure. CSL rates it for excellent tolerance to airborne chemicals. In acid plants, it handles acid vapour and occasional splash, as our sulphuric acid and fertiliser plant case studies show. However, CSL did not design it for pooling or immersion. So where severe splashing or pooling is likely, ask CSL to confirm suitability first.

Unlimited recoat window. You can overcoat it with more Si-COAT 579CM at any time. First, though, clean the old surface of dust, grease and salt.

Si-COAT 581CM Clear: See What Is Happening Underneath

Si-COAT 581CM is the clear version. It dries to a clear, semi gloss film, so you can still see the surface underneath. For corrosion maintenance, that is a real advantage. Inspectors can spot fresh rust, a cracked weld or oil weeping from a flange or gasket without cutting the coating open. It also keeps original colours, markings and safety labels visible on machinery and equipment.

Preparation and application follow the same rules as 579CM. First, clean to SSPC SP2, SP3 or SP12 WJ-4, then spot prime edges, welds, bolts and pits. After that, apply a top coat of 0.2 to 0.5 mm once dry (8 to 20 mil). At 25°C it is tack free in 60 minutes and reaches full properties in 7 days. CSL lists it for structural steel, bridges, machinery, tank exteriors, metal roofs and cladding. However, the test results on this page come from 579CM, so ask us before relying on them for 581CM.

Surface Preparation

First, remove all dirt, grease, oil, loose rust and loose mill scale. Also remove any paint that is peeling, flaking, cracking or blistering. Any old coating you keep must pass the ASTM D3359 tape test at 4A or 4B. Then feather back any lifted edges.

The TDS gives three preparation standards. These are SSPC SP2 hand tool cleaning, SSPC SP3 power tool cleaning, or SSPC SP12 water jetting to at least WJ-4. For water jetting, it also limits soluble salts, including chlorides below 7 ppm (10 µg/cm²). That matters on coastal sites.

Concrete plinths and bases. On site, we have carried Si-COAT 579CM from concrete plinths straight onto the steel in one continuous coat. That way, there is no joint at the base where water can get in. Reliant Energy in Texas did the same on its transmission tower bases. First, though, remove laitance, release agents and any wax or resin based curing compound, because the coating will not bond to them. Then do an adhesion test on the concrete before you start.

Applying the Coating

Mixing: it is one part, so there is nothing to combine. Still, stir it with a powered agitator for at least 5 minutes.
Spot priming: first, brush a stripe coat onto edges, welds, bolts, corners and pitted areas. Aim for about 0.13 mm dry (5 mil, 127 microns).
Full coat: then apply about 0.2 to 0.5 mm once dry (8 to 20 mil, 203 to 508 microns), to suit the steel. That works out to roughly a third to three quarters of a litre per square metre, before losses.
Method: CSL recommends airless spray. Brush or roller also suit smaller areas, as long as they reach at least 0.2 mm dry.
Conditions: keep the surface between 5°C and 60°C and at least 3°C above the dew point.
Cure at 25°C and 50% humidity: it skins over in 25 minutes and is tack free in 60 minutes. After that, it dries in 4 to 6 hours and reaches full properties in 7 days.
Colours: grey and off white as standard, and clear as Si-COAT 581CM.

The Si-COAT CM System for C5 Environments

For the harshest coastal, marine and heavy industrial sites, CSL pairs Si-COAT 579CM with CSL 979 primer. CSL 979 is a two pack epoxy zinc phosphate primer. Together, the system builds about 0.3 mm: roughly 150 microns of primer and 150 microns of Si-COAT 579CM.

An independent laboratory tested the system as a whole. It passed ISO 12944-6:2018 cyclic corrosion testing for C5 High, over 1,680 hours and 10 cycles. It also passed 2,500 hours of ASTM B117 salt spray. However, these results cover the system with CSL 979 only. Si-COAT 579CM on its own does not carry a C5 rating.

The primer is also less forgiving than the topcoat. CSL recommends abrasive blasting to SSPC SP6 or Sa 2 under it. On some maintenance work, power tool cleaning may do instead. In addition, the primer needs air temperatures of 25°C to 40°C and relative humidity below 75%. On the KwaZulu-Natal coast, that narrows the working window, so plan the primer days carefully.

Where Si-COAT 579CM Is Used

Mining and mineral processing. Mine steel, conveyors and tanks face dust, moisture and process fumes. On top of that, they rarely come out of service for blasting. For example, at the Escondida copper mine in Chile, it replaced failed epoxy in desert, high altitude conditions. See our article on mining corrosion protection.

Chemical and fertiliser plants. Structures exposed to acid vapour and occasional splash. This is where the 579 track record in our case studies is strongest.

Tanks and terminals. Tank exteriors, pipe racks and supports at fuel and bulk terminals, as our article on silicone coating for petroleum tanks explains.

Bridges and structures. Bridge steel and structural frames that cannot close for blasting. Read more on bridge corrosion protection.

Power and electrical. Transformer casings, substation steel and pylons. For instance, in Chile it protects transformer casings alongside our high voltage insulator coating.

Coastal and harbour steel. Steel in salt air along the KwaZulu-Natal and Western Cape coasts. On the worst exposures, however, the CM System is the better choice. Our guide to anti-corrosion coating for South Africa’s climate covers each region.

Silicone Corrosion Coating vs Conventional Systems

Conventional systems usually need abrasive blasting first. Then come a zinc rich primer, an epoxy intermediate coat and a polyurethane topcoat, each with its own overcoat window. Over time, the organic topcoat chalks and fades under strong UV.

Si-COAT 579CM, by contrast, goes onto hand tool, power tool or water jet cleaned steel in one coat. It also has an unlimited recoat window. And where a site needs C5 performance, the CM System with CSL 979 covers it. For a wider view, see our page on industrial coatings in South Africa or the Si-COAT 579CM FAQ.

For full technical data, download the data sheets below or contact us directly.

View Si-COAT 579CM FAQ