STRESS-CORROSION CRACKING CHARACTERISTICS OF A RANGE OF PIPELINE STEELS IN CARBONATE-BICARBONATE SOLUTION

Stress corrosion cracking (SCC) characteristics of a range of pipeline steels immersed in a carbonate-bicarbonate solution were studied in terms of the deleterious effects of small-amplitude cyclic loading on threshold stress, together with the increase of crack nucleation and the decrease of average crack growth rates with increasing test times. Data were reported on conditions for coalescence or otherwise of adjacent cracks in terms of spatial separation. The time dependence of crack nucleation rates and crack growth in laboratory tests varied with stress. The laboratory rates for crack nucleation and growth likely are applicable in high-pressure gas transmission pipelines in service, but values of the constants in the power law expressions for those rates differed for service conditions. The data showed service condition calculations can be guided by empirically assigning ranges of values for the constants by imposing boundary conditions that relate to service experience. Ranges of values also reflected service experience in relation to variability of service lifetimes for pipe joints that developed cracks.