Preliminary results from the analysis of stone tablets from the National Materials Exposure Programme (NMEP)

As part of a U.K. National Materials Exposure Programme, samples of stone and metals are being exposed at 29 sites for a minimum of 4 years. The sites were chosen to cover a wide range of environmental conditions, climate and topography. Information on meteorological conditions and atmospheric pollutants are being collected from all the sites. Four of the sites also form part of an international programme that is operating concurrently for the United Nations Economic Commission for Europe (UNECE). Results are reported from the exposure test on bare mild steel, galvanized steel, painted steel, copper and aluminium. Rates of corrosion in industrial areas are well below those reported for similar sites in 1930–1960, mainly because of the large fall in sulphur dioxide concentrations, and in many cases the scale is becoming increasingly protective. Rates for aluminium are extremely low. The measured mass losses have been fitted to a variety of simple multivariate correlation functions. Work using continuous corrosion monitors suggests (in agreement with the mass-loss data) that: 1. (i) the rate of corrosion of steel is controlled in British conditions mainly by the long-term average sulphur dioxide concentration, and scarcely responds to short-term SO2 episodes; 2. (ii) nitrogen oxide concentrations have little effect on the rate of corrosion; 3. (iii) the chloride content of rain is not a very important factor for steel corrosion rates except at a few coastal sites.