IRON RUST

Evening Post, Volume CVII, Issue 61, 15 March 1924, Page 24

IRON RUST

WHAT AMERICA LOSES EACH YEAR STRANGE AND SURPRISING FACTS. Strange and surprising facts are brought out in a scientific investigation into the causes of iron and steel corrosion, extending over twelve years. The annual wastage from such corrosion is estimated at over three billion dollars. Ttie conclusions are embodied in a report made to the Engineering Foundation by J. Vipoud Davies, of iNew York, president of the United Engineering Society, states the "New York Times." Research work has shown that sea water, water in alkaline coils or water percolating through "fills" containing some kind ot chomical wastes are the commonest attackers of iron and most discoverable in the piping of water and sewage systems, tunnel linings, and other engineering structures, it has been observed that certain kinds of soil and water act' upon cast-iron, slowly softening the metal until it can be cut with ah ordinary pen-knife. Equally strange- is the established fact that iron thus softened grows bard again when exposed to the air.

Four big national organisations—civil, mining, mechanical, and electrical engineers—sponsored the research- work in the endeavour to find ways of eliminating this ircjn-softening process ot graphitic corrosion. In his report Mr. Uavies says:

"I exposed many samples of iron under various conditions for periods of one to fire years. Some samples wore completely graphitised in one year. Others close by were litllo affected in the longer periods. This corrosion was found to have no relation to electrolysis by stray electric currents, but to be due to action ■within the metal itself, to direct electrochemical process. In the situation where the experiments were conducted the graphitic corrosion was traceable to the injurious action of the water percolating through the soil in which the specimens of iron were buried. Exhaustive electrical surveys proved that there were no stray currents present. "The distinctive action is due to a great number of ■■ tiny battery cells made up of the particles of iron' and carbon in the casting, the alkaline or salt or slightly acid water serving as the electrolyte. Contact with metals lower in the electro-motive series or stray electric currents hasten the action. 'White" castiron, containing less graphite, is but little attacked. -Cast-irons high in silicon are non-corrosive. Unfortunately, they are brittle, difficult to melt, cannot be machined, and consequently are not used in engineering structures. "Protective measures consist of keeping the electrolyte (injurious water) away from the surface of the casting or of neutralising its action. Failing in these, if the castings are of a kind of iron subject to attack, one can only follow the practical example of the ciicu? man who exhibited a lion and a lamb peacefully occupying the samo cage and found it necessary occasionally to renew the lamb. ■ .

"Cast-iron affected in this way has been found along our coasts, in tidal marshes, in the alkaline soils of Manitoba, and i n many other places. Some of the phenomena mentioned are due to well-known facts.. The 'grey' cast-iron, the kind most readily attacked, contains several per cent, of'carbon by weight. 13eing much lighter than pure'iron, the caroon is a- considerable proportion of this bulk of the castings. The cabon is not dissolved by the salt or alkaline water, wbi-.h slowly eats away the iron. •Hence,' although the dimensions of the casting many remain unchanged, its specihe gravity and its weight will be reduced.".