Framing systems in hostile environments

Aluminium in open air:
The corrosion of metals in open air environments depends on the so-called time of wetness and the composition of the surface electrolytes. The time of wetness refers to the period during which a metal’s surface is sufficiently wet for corrosion to occur. The time of wetness is normally considered to be when relative humidity exceeds 80% and, at the same time, the temperature is above 0°C (e.g. when condensation forms). In normal rural atmospheres, and in moderately sulphurous atmospheres, aluminium’s durability is excellent. In highly sulphurous atmospheres, minor pitting may occur. However, the durability of aluminium is generally superior to that of carbon steel or galvanised steel. The presence of salts (particularly chlorides) in the air reduces aluminium’s durability, but less than for most other construction materials. Maximum pit depth is generally only a fraction of the thickness of the material. Thus, in marked contrast to carbon steel, strength properties remain practically unchanged.

Field exposure tests
In a range of outdoor atmospheres, the Swedish Corrosion Institute has carried out field exposure tests on untreated metals. For plates that had received no surface treatment, the weight losses after eight year’s exposure are given here. After the eight years, the average.

Pit depth in the aluminium plates was 70 µm (0,07 mm). The bar chart below shows that aluminium’s weight loss near the sea was:

Approx 1/100th that of carbon steel (Fe)
Approx 1/10th that of galvanised steel (see Zn in the bar chart)
The rate of corrosion decreases rapidly with distance from the sea. Approximately 1 km from the sea, aluminium behaves more or less the same as it does in a rural atmosphere. The corrosion rate of the pits decrease with time.

The picture below shows an untreated sample after 20 years off the south-west coast of Sweden. UV radiation, sulphuric acid and nitric acid in combination with chlorides have not left any deep marks. After 22 years in a marine atmosphere, examination of an untreated aluminium sample (alloy AA 6063) showed that corrosion attack was so limited (max. depth approx. 0,15 mm) That strength was not affected.

The picture above shows an untreated sample after 20 years off the south-west coast of Sweden. UV radiation, sulphuric acid and nitric acid in combination with chlorides have not left any deep marks. After 22 years in a marine atmosphere, examination of an untreated aluminium sample (alloy AA 6063) showed that corrosion attack was so limited (max. depth approx. 0,15 mm) That strength was not affected.
In conclusion we can confirm that our support systems are suitable for marine environments.

In conclusion we can confirm that our support systems are suitable for marine environments.