1, 000l/hr humid air, contaminated with 40ppm SO₂, was continuously fed to a test chamber (about 1151 capacity) by Yamasaki's Constant Volume Gas Pumps (USA Pat. No. 3479801). The relations of stationary concentration of SO₂ gas in the chamber and corrosion rate with the number of specimens of mild steel and aluminum plate respectively were obtained under the conditions of dew-cycle (25-50°C/60-60min) and constant temperature (30°C and 50°C).
The corrosion rate in the dew-cycle test was higher than that in the constant-temperature test at the maximum temperature in the dew-cycle test. The decrease of stationary SO₂ concentration in test with specimens corresponded to the increase of corrosion rate.
It is important for the reproducibility of an accelerated test to provide not only the concentration, but the flow rate of the contaminated air and the number or the total surface area of the specimens to be tested.

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The corrosion of Cr steels containing 5 to 30% Cr exposed to dry hydrogen chloride gas and to dry chlorine gas at elevated temperatures was investigated.
The results obtained are as follows;
1) In hydrogen chloride at any temperatures below 500°C, 13% Cr and 18% Cr steels have the highest corrosion rates of all the specimens tested. At longer exposure times, there is a tendency for Cr steels to decrease in corrosion rates with time. This is related to the formation of protective surface films which mainly consist of ferrous chloride.
2) Cr steels are corroded more severely in chlorine than in hydrogen chloride gas. Mild steel is found to ignite in chlorine gas above 250°C. The addition of chromium improves the corrosion resistance to chlorine gas effectively. The corrosion rates obtained in short exposure time are nearly equal to ones in longer exposure time. This is concerned with volatility or melt of the corrosion products.
3) Corrosion rate increases more rapidly in chlorine gas with rise of testing temperature than in hydrogen chloride gas.

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