SEDL / STP / STP821-EB / STP34443S

Threshold-Stress Determination Using Tapered Specimens and Cyclic Stresses

Fessler, RR
Department Manager, Transportation and Structures, and Principal Research Scientist, Battelle Columbus Laboratories, Columbus, Ohio

Barlo, TJ
Department Manager, Transportation and Structures, and Principal Research Scientist, Battelle Columbus Laboratories, Columbus, Ohio

Pages: 15    Published: Jan 1984

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Abstract

Traditional methods of determining the threshold stress for stress-corrosion cracking involve testing a number of specimens that are loaded to various levels of constant initial stress. In research sponsored by the Pipeline Research Committee of the American Gas Association, it was shown that low-frequency, small-amplitude cyclic loads superimposed on a constant load can reduce the threshold stress substantially. Since such loading can occur on real structures, it was felt that the threshold stress should be determined under those more severe and realistic conditions. Furthermore, by using a specimen with a tapered gage section, a range of stresses could be evaluated in a single test, making it possible, in principle, to determine the threshold stress with one or two specimens. Test procedures involving tapered specimens and cyclic loads superimposed upon a constant load are described, and representative data for various line-pipe steels are presented. The test environment consisted of a water solution of sodium carbonate and sodium bicarbonate, and the temperature was controlled at 352 K (175°F). The potential was controlled potentiostatically at the center of the range in which stress-corrosion cracking occurs. Test durations typically were 1 to 2 weeks.