Stress corrosion cracking (SCC) is the result of a combined effect of tensile stress and a corrosive environment. Buried natural gas transmission pipelines are known to incur this mode of cracking in places where protective coatings have broken down, exposing surfaces to the groundwater. It has recently been discovered that Canadian pipelines are susceptible to a unique form of pipeline SCC, dubbed non-classical. Research into this phenomenon is still in an infant state, whereas classical pipeline SCC has been actively studied for over twenty years.

A test apparatus was previously developed at the University of Waterloo to reproduce non-classical SCC and measure corresponding crack growth rates. No cracking was produced during preliminary trials. Accordingly, several modifications have been made and a further series of tests conducted.

Classical SCC was successfully reproduced in a pipeline steel under cyclic loading with pre-cracked specimens held at -650 mV SCE and 75°C. A maximum average growth rate of 2.7 x 10^-7 mm/s was measured. Minimum threshold levels were obtained for crack tip strain rate, 2.3 x 10^-8 s^-1, and for stress intensity, 25 MPa-m^1/2. These values agreed well with similar results in the literature. Tests with plain specimens in the nonclassical environment produced very small cracks, on the same scale as documented findings. Non-classical tests using pre-cracked specimens did not exhibit signs of growth. Several salient issues were also addressed during the current course of study. Previous research had identified a fracture surface feature comprised of crystallographic planes and partially exposed grain boundaries as indicative of SCC propagation. Contrary to this,