On the Corrosion of Copper-Nickel Base Alloys by Water and Steam at Elevated Temperature. (Corrosion of Copper Alloys in Hot Water and Steam. (5))

Abstract

An investigation has been made to determine the corrosion resistance of binary and commercial copper-nickel base alloys in water and steam at elevated temperature. The tests were conducted by exposing the specimens to degassed or oxygen bearing water and steam at 200° to 350°C under saturated pressure for 250 hours. The results obtained were as follows: (1) In perfectly degassed condition, corrosion by water and steam increased with increasing of nickel content of alloys, but no severe corrosion was observed. (2) In oxygen bearing condition, severe corrosion of exfoliating, pitting, or intergranular type was observed on Cu-10∼90%Ni alloys except Monel metal by exposure to water and steam at 300° or 350°C. The exfoliating corrosion which was observed in above test was similar to that we have ever experienced in 70-30 cupronickel tubes used in feed water heater of power plant. (3) It is considered that severe corrosion by oxygen bearing water or steam at elevated temperature is due to the action of hydrogen gas which is evolved at the metal surface by selective oxidizing reaction of water and steam to exfoliate the oxide film. (4) Corrosion resistance of Monel metal containing 1.24% of iron to oxygen bearing water and steam is superior to that of binary alloys. This fact shows that iron is effective to form the protective films.