Identifying sulfide stress cracking stages on a HSLA pipeline steel in H2S environment by electrochemical noise

Abstract

Abstract Sulfide stress corrosion (SSC) in high strength low alloy (HSLA) pipelines was investigated in the work. Ultrasonic inspection and in-situ electrochemical noise (EN) measurements were carried out during stress corrosion experiments to monitor the progress of sulfide stress cracking in H2S environment. Moreover, the interrupt experiments were employed to reveal the evolution of corrosion morphology during SSC through the analysis for the EN signals. Microstructural characterization was also performed to identify the morphological evolution owing to the stress corrosion. It is found that the process of SSC is divided into three stages: uniform corrosion stage, pitting or local corrosion stage and cracks propagation stage. The period of time that the uniform corrosion transforms to the local/pitting corrosion is in the range of 12-24 h. The EN analysis results, such as time-domain curves, power spectral density (PSD) diagrams, energy distribution plots (EDPs) and current kurtosis, correspond to the microstructure observation and ultrasonic inspection. Especially, the recognition of crack initiation by current kurtosis curves correlate well with that by the ultrasonic inspection, which suggests that the current kurtosis analysis could provide the information for crack initiation in real time