Effect of Solutions on the Endurance of Low-Carbon Steel Under Repeated Torsion at 482 F (250 C)

Abstract

The stresses to which the steel in a boiler is subjected may be divided into (a) static stresses and (b) repeated stresses. A great deal of experimental work at boiler-water temperatures has been directed toward the determination of the effect of solutions on the physical properties of the steel as measured by static tests, but repeated-stress testing under these conditions has received comparatively little attention. In the investigation discussed in this paper, repeated torsion testing with a rather slow repetition of the stress was used to measure the comparative effect of air, water, sodium hydroxide, and other solutions on steel at 482 F. Under the conditions investigated it was found that water caused failure more rapidly than air, and sodium hydroxide caused failure more rapidly than water. Sodium chloride and sodium sulphate in water solution had no different effect from that of water alone. Sodium carbonate and tri-sodium phosphate in water had about the same effect as sodium hydroxide. The addition of sodium carbonate in solution, or sodium sulphate as excess solid to the sodium hydroxide did not prevent the action of the sodium hydroxide in these repeated torsion tests. It was found that by the addition of either sodium or potassium chromate, or sodium nitrate to the sodium-hydroxide solutions, the action of the sodium hydroxide could be prevented and the endurance of the specimen under the test conditions could be brought up to a value at least as high as that for water alone. The endurance of the specimens does not appear to have been directly related to surface corrosion or pitting.