Experiments to determine the critical pitting temperature of several alloys in calcium bromide solutions using the ASTM G150 electrochemical critical pitting test procedures. Similar experiments were also conducted in solutions containing equal concentrations (by weight) of chlorides and bromide.

Components in upstream Oil and Gas production such as flowlines, storage vessels or injector pipelines which are made of duplex stainless steel UNS S32205 can undergo localized corrosion such as pitting or crevice corrosion when exposed to oxygen during shutdowns or turn arounds. Such unintended exposure to oxygen is related to poor maintenance or improper preservation and would normally require replacement of equipment. Further use of such pitted components can be considered but requires re-assessment of the pre-corroded material. Open-circuit Potential (OCP) and repassivation potentials (Erp) were measured on UNS S32205 in simulated flowline brines containing 150,000 mg/L Cl- at 110oC with pCO2 of 4.1 bara. The effect of pre-pits on bare and girth welded UNS S32205 was determined by creating artificial pits at OCP under oxygenated brine conditions and then switching the gaseous environment to sweet (CO2) conditions with continuous OCP monitoring. It was found that in oxygen-free CO2 production environments, existing pits did not grow. Sulfide Stress Cracking (SSC) resistance of pre-pitted solution annealed UNS S32205 specimens was determined through Slow Strain Rate Testing (SSRT) and Ripple Load Testing (RLT) at 90oC in concentrated chloride solutions. An electrochemical method was applied to create a single pit on the gauge surface. Comparison of SSRT and RLT results showed that SSRT is too aggressive for determining the pH2S limits. RLT of both pristine and pre-pitted UNS S32205 in concentrated chlorides with up to 0.3 bara pH2S did not show rupture, while selective attack of the ferrite phase was found (pit-depth < 30µm). RLT of notched UNS S32205 specimens were compared to that of pre-pitted specimens. Implications of these results on the limits recommended in ISO15156 / NACE MR0175 are discussed.