The effect of concentration of an organic imidazoline as inhibitor on internal stress corrosion cracking (SCC) behavior of an API X70 pipeline steel exposed to a brine solution was studied. The SCC process using simultaneously the slow strain rate stress test (SSRT) and electrochemical measurements was performed. Fracture surface analysis and secondary cracking were observed through a scanning electron microscopy (SEM). According to SEM fractography and SSRT results, the steel showed high SCC susceptibility with a brittle fracture and several secondary cracks without addition of inhibitor, whereas the addition of inhibitor to brine solution was effective to increase the SCC resistance of steel at concentrations of inhibitor of 50 and 100 ppm. A further addition of concentration of inhibitor had a negative effect on the mechanical properties of the steel. Electrochemical measurements results are in accordance with the SCC susceptibility, indicating that corrosion inhibitor film suppressed the anodic and cathodic reactions increasing the resistance to SCC until concentration of 100 ppm. Further addition of inhibitor aggravated the localized corrosion due to local desorption of inhibitor molecules. The Hilbert–Huang transform (HHT) analysis revealed the contribution of different corrosion process contained in the electrochemical current noise (ECN) signals at several inhibitor concentrations.

This work presents the effect of a "green" rust converter applied on surface of a carbon steel sample immersed in seawater using an electrochemical noise (EN) technique. Working electrodes was made of carbon steel (with rust, with rust and converter and bare samples) and the saturated calomel electrode was used as reference electrode. The highest corrosion rate (CR) was obtained in the bare samples (samples without rust and converter) and the lowest CR was obtained in the samples with rust and converter, this behavior was attributed to the magnetite and iron tanates. A stable behavior was observed in samples with rust and converter during all exposure time. The localization index for the rusted sample and rusted sample with converter showed a mix process while the bare sample showed a general corrosion. It is important to point out that in all optical micrographs was possible to observe a localized corrosion type.

Stress corrosion cracking (SCC) process of an API X60 steel exposed to a brine solution with and without addition of corrosion inhibitor was analyzed through electrochemical noise (EN). A NACE brine solution without and adding 100 ppm of inhibitor was used like electrolyte at atmospheric pressure and 60°C. The SCC assessment was carried out using slow strain rate tests (SSRT) at strain rate of 1x10-6s-1in accordance with NACE TM-198. During SSRT the SCC process was monitored using EN using a set up with three electrodes. A decrease in mechanical properties for samples without corrosion inhibitor was observed. The SCC index obtained from the mechanical properties of SSRT indicate that X60 steel could be susceptible to SCC in brine solution without adding corrosion inhibitor. The time series show fluctuations with high frequency, but of low amplitude (for current and potential) which indicate the presence of a type of localized corrosion, which was corroborated with the index location calculated, where a mix corrosion process type was obtained. A clear effect of corrosion inhibitor was observed, which decrease the corrosion rate considerably.