CORROSION BEHAVIOR OF STEELS IN GEOTHERMAL STEAM POWER PLANT.

The steels investigated in the power plant were a plain 0. 14% C steel, weathering steel with 0. 09% C, 0. 74% Cr, and very small amounts of Mo and V, and steels with up to 13% Cr. Tests were conducted in the atmosphere, cooling water, hot water, and in a test loop simulating the steam well. Atmospheric corrosion could be reduced 50% by using the weathering steel. Resistance to condensed water was not improved by small amounts of alloying elements, as in the weathering steel. Corrosion by hot water decreased sharply with additions of Cr. Attack was almost negligible above 13% Cr. High Cr contents were also beneficial under steam/water two-phase flow which may cause severe erosion-corrosion to carbon steel. The failure of casing tubes experienced in practice is caused by erosion-corrosion initiated at areas where the flow is disturbed by unfavorable design such as slots in the pipe or gaps at couplings. Surface irregularity caused by corrosion is also detrimental.