The effect of the water-saturated supercritical carbon dioxide flow rate on the corrosion behaviour of API 5L X80 steel at a temperature of 35 oC and pressure of 80 bar was investigated. Tests were carried out with the samples attached to a rotating shaft inside an autoclave. Results indicate that increasing the scCO2 flow rate had no significant influence on the general/localized corrosion rate under the various dynamic conditions considered. The average general corrosion rate was 0.064 mm/year, while the average measured pitting penetration rates were one order of magnitude higher. The size of the corrosion features on the surface of the samples, which were believed to provide an indication as to the size of the condensed water droplets, were much smaller than the calculated critical droplet size needed to be displaced by the flow, supporting the theory as to why flow rate had little effect on the corrosion response.

The influence of temper temperature on the environment assisted cracking of seamless 9% Ni steel tubes were investigated using scanning electron microscope (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), slow strain rate tensile (SSRT) tests, hydrogen permeation tests and electrochemical measurements. Mechanical and electrochemical tests were conducted in sodium thiosulphate (Na 2 S 2 O 3 10 −3 mol L −1 ) solution at open circuit potential (OCP) and at cathodic potential. Results showed that 9% Ni steel had a higher ductility loss at OCP when compared with the results obtained under cathodic potential. The lower ductility loss at cathodic potential was attributed to the inhibition of the anodic dissolution. After the tests, the specimens were examined using scanning electron microscopy to characterise the fracture morphology. The fracture surface exhibited mixed morphology, with a ductile morphology in the centre and a brittle morphology near the edges.

The effect of calcium ions (Ca<sup>2+</sup>) on corrosion of API 5L X80 carbon steel in carbon dioxide (CO<sub>2</sub>)-saturated brines was studied. Tests were carried out in brines containing 0, 1000 or 5000 ppm of calcium ions with a constant chloride ion concentration, at temperatures of 35 and 60 <sup>o</sup>C, and pressure of 80 bar. The corrosion rates were determined by mass loss, and the protective properties of the film was evaluated by carrying out electrochemical measurements in a separate vessel containing a standard brine. The results showed that adding Ca<sup>2+</sup> to the brine slightly reduced the average corrosion rate, even in the absence of a crystalline corrosion product scale. For longer exposure times, it promoted the growth of a mixed iron-calcium carbonate (Fe<sub>x</sub>Ca<sub>y</sub>CO<sub>3</sub>) scale with increasing calcium molar mass, shifting the scale morphology from prismatic crystals (pure FeCO<sub>3</sub>) to globular (mixed carbonate). At 35 <sup>o</sup>C the mixed iron-calcium carbonate scale offered better protection when compared to the pure FeCO<sub>3</sub> scale counterpart. However, at 60 <sup>o</sup>C, where a thicker carbonate scale was formed, the increase of Ca<sup>2+</sup> content had a minimal effect on the corrosion rate.