No abstract

The distribution of the galvanic corrosion of a nickel-to-steel couple in open, slowly moving, tap water was estimated from measurements of potential differences in the water around the couple. The distribution was confirmed later by thickness measurements. The two methods were in excellent agreement. The maximum galvanic corrosion of the steel occurred at the junction of the two metals and decreased as the distance from the junction increased. The maximum effect at the junction was 3~ times the average galvanic corrosion. The normal uncoupled corrosion of the steel was greater than the average increased corrosion due to the galvanic effect despite the three-to-one area ratio of nickel to steel. Potential measurements can be made as soon as a steady state is reached, but it usually takes considerable time for corrosion to become extensive enough for thickness measurements to be accurate.

Stress corrosion tests have been run in pressurized water at 600 F (316 C) using double U-bends and double bent beam specimens. The tests were conducted in autoclaves for up to 3000 hours. The composition of the gas phase above the water and the pH were controlled. The materials tested were commercial heats of Inconel (1) 600, Inconel 625, lncoloy(1) 800 and stainless steel Types 304, 304L and 347; some Inconel alloy 600 weldments; and some experimental laboratory compositions. Several heat treatments were included. No attack was observed in specimens stressed at 90 percent of room temperature yield strength. No attack was observed when hydrogen constituted the gas phase. No attack was observed when crevices were absent. The combined action of a high stress, a high oxygen concentration and a crevice did promote intergranular attack and cracking in the crevice area in all alloys tested. The severity of the attack increased with the oxygen concentration. Many specimens heated for 2 hours at 1250 F (677 C) showed deeper attack than annealed specimens. Solution heat treatment, low carbon content or the presence of carbide stabilizers did not eliminate the attack. The behavior of weld metal deposits was not significantly different from that of base plate. Variations in composition within the normal range of Alloy 600 were unimportant. Differences in behavior among the several alloys tested were minor compared to those from environmental effects.

Numerous tests have shown that Alloy 600, a 76 nickel-15 chromium-7 iron alloy, has excellent corrosion resist­ance in pressurized high temperature water. The present tests were undertaken to determine the influence of possible contaminants in 600 F (316 C) pressurized water on corrosion behavior, using both single and double U-bend specimens. The double U-bend provided a combined stress and crevice specimen. Contaminants were sodium fluoride, air, lead powder, lead oxide, a petroleum hydrocarbon, and a mixture of lead powder and the hydrocarbon. Contamination and aeration were much in excess of any condition likely to be encountered in pressurized water reactors. Under certain conditions, some contaminants induced stress corrosion cracking.

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