Corrosion protection

In many applications corrosion rates are  low and do not cause structural concern.  However, if corrosion is not considered at the design stage, it can result in an unpleasant appearance if the Bi-Steel is exposed. A number of effective methods of protection are available. The table below illustrates typical annual corrosion rates for various environments:

 

 

Environment	Corrosion Rate (microns/year)
Internal dry surfaces	< 1
External atmospheres with low level of pollution, generally rural areas	1 - 25
External urban and industrial atmospheres with moderate sulphur  dioxide pollution. Also coastal areas with low salinity	25 - 50
Industrial areas and coastal areas with moderate salinity	50 - 80
Industrial areas with high humidity and aggressive atmosphere.  Coastal and offshore areas with high salinity	80 - 200

 

Internal surfaces do not require protection

Bi-Steel face plates are only subject to corrosion from one side.  The internal surfaces are protected by the alkaline environment associated with the concrete.  This is the same process that protects the steel inside reinforced concrete.  Unlike reinforced concrete, the interior of a panel is hermetically sealed by the face plates and micro-cracking of the concrete does not result in atmospheric pollutants getting to the steel.

Protection methods

Where the exposed Bi-Steel face plate needs protection there are a number of options:

• Increasing plate thickness to allow for corrosion. This method can be used if the corrosion rate is relatively low.
• Application of a protective coating
• Cladding the Bi-Steel
• Cathodic protection (where the steel is submerged)

Often a combination of systems is used.

Where a corrosion protection system is required, then these can be used with confidence.  There are numerous products available that are widely accepted by specifiers.  Many of these have been developed and improved over many years, and can provide the confidence required for most applications.  For less typical applications Tata Steel can provide specialist advice, drawing on its extensive experience in designing corrosion protection systems.