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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 high resistance to corrosion. 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, and damage by abrasion, cutting or machining is quickly repaired.
Grade 304 has excellent corrosion resistance in a wide range of media. It resists ordinary rusting in most architectural applications. Exposure of a particular grade of stainless steel to a more aggressive environment than it can resist will result in tea staining and or pitting and corrosion. Grade 316 should be selected as a minimum within five kilometres of the surf. The less expensive grades (such as 304 or 430) 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 ensuring that your new security doors and screens will look great for years with a moderate amount of maintenance.
Corrosion - Why Are Some Products More Likely To Corrode?
When two metals are connected and in contact with a conducting liquid, the more active metal will corrode and protect the noble metal. Aluminium is more negative than stainless steel and so the aluminium will corrode to protect the steel at scratches or cut edges. The stainless steels, including 304 and 316, are more positive than aluminium, so when stainless steel is in contact with aluminium and is wet, the aluminium will corrode first, while the stainless steel will be protected by this galvanic activity and will not corrode. The rate of galvanic attack is governed by the size of the potential difference.
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.
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