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About Invisi

Stainless Steel - The Facts

Stainless steel is a generic term for a family of corrosion resistant alloy steels containing 10.5% or more chromium. All stainless steels have a higher resistance to corrosion than their mild steel counterparts.

This resistance to attack is due to the naturally occurring chromium-rich oxide film formed on the surface of the steel. Although extremely thin, this invisible, inert film is tightly adherent to the metal and extremely protective in a wide range of corrosive media. The film is rapidly self-repairing in the presence of oxygen. Damage by abrasion, cutting or machining is quickly repaired.

Grade 316 should be selected as a minimum within five kilometres of the surf.

The less expensive grades (such as 304) will probably become tea stained or even suffer more severe corrosion. Grade 316 has excellent corrosion resistance in a wide range of media. Its main advantage over grade 304 is its increased ability to resist pitting and crevice corrosion. It resists ordinary rusting in virtually all architectural applications, and is often chosen for more aggressive environments such as sea-front buildings and fittings on wharves and piers.

Grade 316 has virtually the same mechanical, physical and fabrication characteristics as 304 with better corrosion resistance, particularly to pitting corrosion.

Invisi-Gard Stainless Steel Security Products use only 316 Marine Grade Stainless Steel.

You can rest assured your new security doors and screens will look great for years with only a moderate amount of maintenance. And unlike some other competing products your warranty is not subject to the ongoing use of a proprietary cleaning product.

The 'Tech Stuff' on Galvanic Corrosion:

Why are some products more likely to corrode?

When two dissimilar metals are connected or in contact and are in the presence of a conducting electrolyte such as water or even dust, the more active metal will corrode and protect the less active metal. Aluminium is more active than stainless steel and will preferentially corrode in the vicinity of the contact zone between the metals. In the case of security screens, the aluminium is more active than the stainless steel mesh or any stainless steel fasteners, and so will corrode first, while the stainless steel will be protected by this galvanic phenomenon. The rate of galvanic corrosion is governed by the size of the potential difference between the metals in contact, and by the conductivity of the electrolyte.

As a rule of thumb, if the potential difference is less than 0.1 volt, then it is unlikely that galvanic corrosion will be significant. In the case of Stainless Steel and Aluminium the current difference ranges from between 0.175 and 0.55 volts depending on the specific alloys concerned. It can be seen that there is a high likelihood that corrosion will occur in any installation where the two metals are allowed to come into contact, either directly, or by way of mechanical fixing.

All Invisi-Gard Stainless Steel Security Products incorporate the Patented EGP Retention Method which locks the 316 Marine Grade Stainless Steel Mesh into the Heavy Duty Extruded Aluminium perimeter framing.

The Pressure Retention Method completely isolates the Stainless Steel from the Aluminium and because it does not rely on screws, or any other form of mechanical fixing, corrosion through dissimilar metals contact is avoided.