Abstract
An extensive study was conducted of the susceptibility of Type 347 stainless steel to stress-corrosion cracking in high temperature water over wide ranges of chloride concentration, temperature, oxygen concentration and pH. No cracking was observed at a chloride concentration of 5 ppm, but cracks were observed at 10 ppm and higher at temperatures of 100C and above. Maximum susceptibility was found between 150C and 250C, but no cracking was found below 100C. No pH effect was noted. Various heat treatments and surface preparations showed no appreciable effect. Nickel plating, even with only partial covering of the surface, was found to inhibit stress-corrosion cracking completely, while chromate and phosphate in solution were effective only at high concentrations.
Five other austenitic stainless steels were similar in behavior to Type 347 stainless steel, and three ferritic stainless steels exhibited only slightly better resistance to cracking. Of five high nickel, high chromium alloys tested, only Inconel exhibited complete immunity to stress-corrosion cracking.
Cast chromium-nickel stainless steels were found to be extremely resistant to stress-corrosion cracking as long as they were not subjected to cold-working or plastic deformation. Once stressed above the yield, the resistance to cracking could not be regained by annealing.
A number of the alloys tested in high temperature water were also tested in boiling 42 percent MgCl2. It was found that the susceptibility of an alloy to stress-corrosion cracking in boiling 42 percent MgCl2 solution is not necessarily a measure of its susceptibility in high temperature water containing relatively small concentrations of chloride ion.
