Stainless Steel Roofing in Four Mining Applications

40 Years Ago

1. Introduction

Initial response to the suggestion of the use of stainless steel as a roofing material was a gasp of disbelief from specifiers, particularly on account of the initial installation cost.  But as can be seen from the following, this application of stainless steel can be a cost saver.

2.  Advantages of Stainless Steel

2.1  The main advantage of stainless steel is, of course, its corrosion resistance. When correct roofs are specified, stainless will give an indefinite life-span, thus negating all the cost normally involved in re-roofing, namely purchase of new material, extra labour and in some instances, downtime on the plant.

2.2  The second advantage is a slight weight saving in that normally stainless steel roof sheeting is specified a gauge thinner then an equivalent application in galvanised mild steel. Since this reduces dead load, there will be a saving in structural material.

3.  Actual applications

fig1

Fig. 1. Processing plant in the Mining and other industrial sectors often require roofing specifications which offset corrosive and acidic fume attack.

3.1. Impala Platinum Refinery – Springs 

The problem at the Nickel Refinery building at this plant is the sulphuric acid fumes which come off the nickel and copper refinery process as by-products.  Previous replacement period for baked-enamel roof sheets was twelve months: Anticipated life of stainless – indefinite.

3.2  Tsumeb Mining Corporation – S.W.A.

The roof giving trouble here was the smelter house.  Sulphuric dioxide comes off the furnace and due to the heat present, condenses on the roof to form sulphurous acid which quickly oxidises to sulphuric acid.

The previous smelter roof was an epoxy coasted mild steel system which lasted 12 years and is now being replaced.  When the smelter extension was built stainless a specified outright.

fig2

Fig. 2. Stainless steel roofing has proved effective in processing plants. This example is at a nickel refinery building in Springs.

3.3  Phalaborwa Mining Company – Eastern Transvaal

As with Tsumeb the roof to the smelter house is attacked by Sulphuric acid.  An epoxy covered roof sheet lasted 6 years in this situation.  Stainless to the rescue!

3.4  Harmony Gold Mine – Orange Free State

Two buildings are affected here; the filter building and the precipitation building.  Externally fumes from a nearby sulphuric acid plant attack both roofs but the filter building is more affected.  The process inside both these buildings gives off a certain amount of sulphuric dioxide which results in internal sulphuric acid attack, added to which hydrochloric acid is also a problem in the precipitation building.

Possibly due to the absence of excessive heat in the working process these two epoxy coated mild steel roofs have lasted for fifteen years but have rotted right through.  Stainless steel roofing is seen as a product which should outlast the life of the mine and perhaps be sold as an asset when it eventually closes.

fig3

Fig. 3. A major advantage of stainless steel roofing, is its ease of maintenance.


4. Conclusion

From the above applications, the cost savings can be seen from the early replacement period of the affected roofing.  We do accept that the nature of most industrial buildings inland are such that the cost benefit will only be felt in 70 – 100 years, but there are certain extremely corrosive areas in which the benefits can be realised within a few years, or even months as we have just illustrated.

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