The first major commercial application of weathering steel came in 1933, when it was used to build coal hopper cars. The exterior of these cars were painted. The weathering steel gave superior performance, and cars with service of up to 25 years showed little corrosive deterioration. Beginning in the early 1940s, extensive atmospheric corrosion studies were conducted under the auspices of the American Society for Testing and Materials (ASTM). These confirmed the beneficial effect of elements Cu, Cr, Si, P, and Ni, singularly or in combination, in an aggregate amount of 2 to 3 percent, on the corrosion behavior of low-alloy steels exposed to various atmospheres, including arid, rural, industrial and marine environments.