Influence of Strain on Current Densities and Stress Corrosion Cracking Growth Rates in X65 Pipeline Steel

High pH stress corrosion cracking (SCC) in gas pipelines has been seen to grow along an incline angle rather than perpendicular to the outer surface. Crack tip strain enhanced electrochemistry has been previously postulated as a reason for the inclination, and recent computer simulations that take this effect into account produce realistic crack paths. This study attempts to determine the effect of strain on the electrochemical response of X65 steel, and the impact that the strain has on growth rates for inclined SCC. Potentiodynamic tests were conducted on X65 tensile specimens with residual plastic strain or in situ elastic strain. An increase of the current density up to 300% was observed within the SCC potential range. Computer simulations were also conducted to show the qualitative effect of this increase in current density on the growth rate, and results indicated that inclined SCC could grow to 50% wall thickness faster than straight SCC if the current density along the inclined angle is 20% higher than along the perpendicular. Further experimental work is suggested that can quantify this current densities’ difference in the strained area around the crack tip.