Session: RIP: Predictive Modeling and Characterization of Corrosion Processes in Complex Environments (In Honor of Professor Digby Macdonald) (Part I of IV)
Predictive Modeling and Characterization of Corrosion and Stress Corrosion Cracking of Pipeline Steels in Groundwater (RIP2026-00062)
The principle of equal electrochemical potential by Professor Digby Macdonald has inspired me in my research. In the case of corrosion and stress corrosion cracking (SCC) of pipeline steels caused by surrounding groundwater, the aqueous electrolytes could be evolved into two different corrosion mechanisms. In the regions with a hot climate, water soluble salts from surrounding soil can be concentrated because of repeated thermal evaporation of trapped groundwater. By contrast, pipeline steels in regions with a colder climate are highly susceptible to low pH or near-neutral pH corrosion since groundwater is unlikely to be evaporated effectively to create electrolytes with sufficient salt concentration to cause high pH corrosion and SCC. The second dilemma situation that is equally important to the nature of electrolytes is how mechanical driving forces play a role in crack initiation and growth. Crack initiation can be very much residual stress dependent, while crack growth is greatly affected either by the magnitude and/or by the fluctuations of pressure, dependent on the type of cracking mechanisms and the stages of cracking. Stage I is associated with repeated crack initiation and growth at the crack surface tip along pipe steel surface where the magnitude and the fluctuation of pressure is critical regardless the types of electrolytes and the mechanisms of corrosion and cracking. In contrast, Stage II cracking where steady state crack growth takes place is sensitive to the magnitude of stress intensity factor in the case of high pH SCC but is affected by a combined effect of both the magnitude and the variation of stress intensity factor for the growth of near neutral pH SCC. The 3rd dilemma situation is related to the metallurgical behaviour of steels, which usually exhibits discontinuous yielding because of low carbon content. In the situation of load control, such as the pressure loading in the pipe hoop direction, discontinuous yielding can lead to a situation of strain shock/high strain rate that accelerates high pH crack growth, while metallurgical features affecting how hydrogen diffuses and is trapped play a key role in the growth of crack in near-neutral pH environments.
