Currently, there is a poor understanding of the effects of pressure related parameters (operating pressure, pressure fluctuations, and hydrostatic testings) on external stress corrosion crack propagation in pipelines in nearneutral- pH environments. A better definition of the role of these parameters on crack propagation is needed to aid in the prediction of crack growth rates on operating pipelines and to develop strategies to mitigate this form of cracking. The objective of the research described in this paper was to determine the roles and synergistic effects of
operating pressure, pressure fluctuations, and hydrostatic testing on crack growth in line pipe steels in a nearneutral- pH SCC environment. All testing was performed on one X-65 line pipe steel in a near-neutral-pH cracking environment, designated NS4. Fatigue precracked compact-type specimens of the line pipe steel were cyclically loaded while immersed in the cracking environment. The desired loading regime was applied using a servohydraulic tensile testing machme. Crack growth was monitored using the electric potential drop technique. The loading conditions applied to the specimen were related to field conditions using the J-integral parameter. It was found that the prior load history applied to the specimens had a significant effect on crack growth behavior.
Overloading inhibited crack growth while unloading stimulated crack growth. Hydrostatic testing, which combines overloading and unload]ng, caused some crack extension but reduced the crack velocity.
Keywords: Stress Corrosion Cracking, Underground Pipeline, Pressure Fluctuation, Hydrostatic Testing, Near-Neutral pH