CAUSTIC STRESS-CORROSION BEHAVIOR OF FE-NI-CR NUCLEAR STEAM-GENERATOR TUBING ALLOYS

Stress-corrosion behavior of Type 304 stainless steel, Incoloy 800, Inconel 600, and Inconel 690 has been measured in both 10 and 50% NaOH environments. Both U-bend and C-ring samples were utilized, and test temperatures were in the range of 600 to 630 degree F. Differences in behavior between the two specimen configurations are attributed primarily to differences in stress level and distribution between the two types of specimens. The C-ring samples of commercially prepared tubing were also exposed at 110% of the room temperature yield strength to strong (50%) mixtures of potassium and sodium hydroxides with and without admixtures of typical sludge species for prolonged periods. The general resistance to caustic cracking increased with the nickel content of the alloy.