During the period 1948 to 1955, specimens of carbon steel and zinc were used to calibrate the corrosivity of the atmosphere of some 19 sites in the United States and Canada. In the period 1960 to 1964 the study was expanded to include some 46 sites around the world.
As in the earlier study, the results at State College, Pa., were considered as unity, and the corrosivity of the other locations were ranked in terms of the corrosivity of the atmosphere at State College. Differences in corrosivity between the two exposure periods were noted in some instances, while in others the atmosphere appeared to remain constant in its action on the two test metals.
In a number of instances the corrosivity of the atmosphere toward steel was greater than its effect towards zinc. In other instances the reverse situation prevailed. In a substantial number of locations the atmosphere was equally aggressive towards steel as it was towards zinc.
When the ratio of the two-year losses between steel and zinc were studied, it was evident that in characteristically industrial locations the ratio was 20 or less; whereas in predominantly marine locations it exceeded 20 and ranged as high as 364.
In a calibration test involving the corrosivity of a marine site at elevations of 60 ft, 30 ft, and ground level, there was little discrimination between elevations by the zinc specimens, but there was substantial discrimination by the steel specimens.
The current work clearly demonstrated, while corroborating the earlier work, that the corrosivity of an atmosphere varies with the metal in question, and that tests must be conducted with the metals of interest. Consecutive two-year exposure tests are more desirable than one-year tests.