Angel of the North

640px-Fly-Angel

The Angel of the North: Image from Wikipedia

At 200 tonnes excluding the concrete piles used to support it, the total cost of The Angel Of The North was said to be £800,000. That means the installed cost for the 200,000 kg was £4 / kg.

The Angel Of The North owes it’s appearance to the weathering steel it is constructed from, these steels are designed to form a stable oxide layer, with a low corrosion rate across the entire surface. This strategy means that it’s possible to have a reasonable service lifetime with a minimum of maintenance, even an initial layer of paint is unnecessary.

Example weathering steel compositions / wt%

Grade C Si Mn P S Cr Cu V Ni
ASTM A242 0.12 0.25–0.75 0.20–0.50 0.01–0.20 0.030 0.50–1.25 0.25–0.55 0.65
ASTM A588 0.16 0.30–0.50 0.80–1.25 0.030 0.030 0.40–0.65 0.25–0.40 0.02–0.10 0.40

Somewhat uniquely for steels, the initial rust layer protects the steel underneath from further deterioration, eliminating the need for paint. This depends on environmental conditions, too much humidity too often mean that the rust layer never reaches a stable point. This can lead to corrosion and loss of integrity.

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