Paper 9: Investigations of Motor Car Corrosion in Finland

Laboratory and field tests on the corrosion of passenger cars in Finland have been carried out. The most critical corrosion points on a car body are located in closed sections. Use of anti-corrosion oil-spraying at the critical points is lowering the corrosion rate. Up to 80 per cent of all cars are treated in this way. The annual cost of this protection is approximately 1–2 per cent of the purchase price of the car.

The garaging of a car has an important influence on the corrosion rate. The important factors are the changes in temperature and the condensation of water in closed sections of the car.

The major part of this investigation is concerned with the use of inhibitors in road salts. In laboratory tests sodium hexametaphosphate shows good protection against corrosion. A higher content of phosphate inhibitor is needed in salt mixtures when sand is present on the roads than is the case with laboratory tests on clear solutions.

Sodium hexametaphosphate reacts with asphalt compounds and the resultant splash from roads makes the windscreen and other parts of the car dirty.

The correlation between the inhibitor additions and the salt mixtures was clear in laboratory tests but quite the reverse in field tests. The reason may be the slow solubility of the inhibitor and its adsorption to the sand and clay.