Abstract
A study is made of the operating and metallurgical variables which govern failure of steel in nitrate solutions. Laboratory tests using a notched C-ring stressed with a cadmium plated, mild steel bolt resulted in no failures for a variety of conditions. A similar specimen stressed in a stainless steel ring between bolts fixed with glass bead insulators produced failures. Some of the conditions for failure were determined using this latter test. When locally stressed above the yield point, carbon steels (N-80 and J-55) failed in hot (150 F–230 F) concentrated (43% and 29%) solutions of NaNO3. Normalized N-80 failed at hardnesses of RC 20 and above. Quenched and tempered N-80 failed at hardnesses as low as RG 17 and AISI 1020 steel on a lower scale at RB 50. Failures were produced in solutions of pH 3 through 8.
Mixed concentrated solutions of sodium nitrate and calcium chloride, in which the CaCl2/NaNO3 ratio was 4, did not produce cracking in either normalized or quenched and tempered N-80 ranging in hardness from RC 15 through RC 36. Failures of RC 32 N-80 were not produced in this mixed solution from pH 3 through 8. Tests were made in solutions of pH 6 in which the CaCl2/NaNO3 ratio was varied from .003 through 4.0 on RC 35 N-80 material. Failures were produced through a ratio of 2.0. The critical ratio for failure is between 2.0 and 4.0 and was not more closely defined than this. Most of these tests were made on API tubing steels, but the results are considered applicable to a variety of low alloy AISI steels. 3.5.8
