Influence of load interaction and hydrogen on fatigue crack growth behavior in steel pipelines under mean load pressure fluctuations

Abstract

Crack propagation in near neutral pH (NNpH) environment causes significant threat to pipeline integrity. Internal pressure fluctuations during pipeline operation create variable amplitude loading condition that can propagate corrosion fatigue cracks in NNpH environments. This study is aimed at understanding the effect of load interaction due to mean load pressure fluctuations on crack propagation in pipeline steel under NNpH conditions. The loading condition involved underload followed by an overload at set intervals among minor cycles. The effect of minor cycles, magnitude of overload, and NNpH environment were considered and compared to control test in air. Results showed optimum reduction in crack growth rate at low magnitude of overload in mean load pressure fluctuation. Mini striations observed on fracture surface suggest the contributions of minor cycles to crack propagation due to load interaction. Significant increase in crack growth at high magnitude of overload in NNpH environment indicates the influence of hydrogen.

A review of crack growth models for near-neutral pH stress corrosion cracking on oil and gas pipelines

“…A similar phenomenon was also observed in small-scale tests: no crack growth was detected in the specimen subjected to a monotonic loading even at the highest stress intensity factor used in the study [33]. It is therefore suggested in [34][35][36] that the growth of NNpHSCC cracks can be better characterized by corrosion fatigue (CF) than SCC. CF is one type of EAC that occurs under the synergistic effects of corrosion and cyclic stress [11,37].…”

“…Many researchers have claimed that cyclic stress is essential to the growth of NNpHSCC cracks [32][33][34][35][36]. Full-scale experiments showed that the absence of cyclic components in the loading spectra led to non-growth of NNpHSCC cracks in pipe specimens and that controlling pressure fluctuations in pipelines resulted in reduced crack growth [32].…”

Effect of corrosion on the fatigue crack propagation properties of butt weld with G20Mn5QT cast steel and Q355D steel in 3.5‐wt% NaCl solution

“…These cracks will converge with the main cracks to accelerate the corrosion FCP, so that the corrosion FCP can be completed at a lower number of cycles. 37 The corrosion FCP is strongly dependent on loading frequency. At a lower loading frequency, the longer the corrosion solution contacts the fresh metal at the crack tip in each cycle, the greater the corrosion damage.…”

The fatigue crack growth behavior of hydrogenated 9Cr‐1Mo steel: An experimental and numerical study

“…HE results in a loss of ductility, which is evident from the occurrence of brittle fracture features observed on the fractured surface. 15,18,19 Several viable mechanisms have been proposed to give insight into this phenomenon, including "hydrogen-enhanced local plasticity" (HELP), "hydrogen-enhanced decohesion" (HEDE), "hydrogenenhanced strain-induced vacancy" formation (HESIV), hydride formation, and "adsorption-induced dislocation emission" (AIDE). [20][21][22][23][24] Out of the proposed HE mechanisms, the HELP and HEDE models of HE mechanisms are mostly accepted.…”