Aluminium in fresh waters

Abstract

The paper summarises research at these Laboratories on corrosion of aluminium in fresh waters. The type of corrosion affecting aluminium depends on water composition. Deep pitting requires oxygen, chloride, carbonate hardness and copper, but the higher chloride contents encourage more general corrosion. Higher carbonate hardness reduces the number of pits formed; sulphates have a similar effect and also increase pit depth. Except in waters of very high copper content, attack is generally less at elevated temperatures. Different alloys differ only slightly in resistance to attack. On superpurity aluminium, pits are slow to form but subsequently penetrate at the same rate as in SIC type. The best form of protection for aluminium is cladding with aluminium– l¼% zinc. This prevents pitting of N3 sheet or tube even in highly corrosive hard waters. Spraying with aluminium–zinc or anodising is also effective. Treatment to form boehmite films gives some protection but is ineffective in the more corrosive waters.