Jakob Enerhaug

Comparison of the Rotating Cylinder and Pipe Flow Tests for Flow-Sensitive Carbon Dioxide Corrosion

Abstract The effects of various hydrodynamic parameters on the corrosion rate of low-carbon steel in carbon dioxide (CO2) environments were studied. Two different flow geometries, rotating cylinder (RC) and pipe flow, were studied simultaneously in the same electrolyte within a glass loop. Comparisons were made over a wide range of parameters: temperature (T) = 20°C to 80°C, pH = 4 to 6, CO2 partial pressure (PCO2) = 0 bar to 1 bar (0 kPa to 100 kPa), velocity (υ) = 0 m/s to 13 m/s. The hydrodynamic conditions studied covered the range from static to highly turbulent flow. The corrosion process was monitored using polarization resistance, potentiodynamic sweep, and electrochemical impedance methods. The comparison of the two flow geometries was carried out in terms of hydrodynamics, mass transfer, and CO2 corrosion. The measured mass transfer rates agreed well with published correlations for the RC and straight pipe (SP) flow. In the case of CO2 corrosion, it was possible to achieve good agreement between...

Factors affecting initiation of pitting corrosion in super martensitic stainless steel weldments

Abstract In the present investigation optical microscopy, in combination with sputtered neutral mass spectrometry (SNMS), has been used to examine the conditions for initiation of pitting corrosion in the heat affected zone (HAZ) of two super martensitic (SM) stainless steel weldments. It is shown that the corrosion resistance depends mainly on the nature of the surface oxide, as determined by the oxygen potential in the shielding gas and the HAZ temperature–time relationship, and less strongly on the underlying microstructure. In the absence of H2S the initiation is associated with spalling of the iron enriched chromium oxide within a narrow region approximately 6 mm from the fusion line, where the contaminated oxide layer is thinnest. As H2S is introduced, the region close to the fusion boundary becomes susceptible to localised corrosion because of the more extensive metal oxidation. Thus, the high temperature oxidation and iron oxide scale formation accompanying the welding operation appear to be the main factors affecting pitting corrosion initiation in SM stainless steel weldments.

Dissolution and Repassivation Kinetics of a 12.3Cr-2.6Mo-6.5Ni Super Martensitic Stainless Steel A Comparative Study

In this investigation, the dissolution and repassivation kinetics of a super martensitic (SM) stainless steel (Fe-12.3Cr-6.5Ni-2.6Mo) have been characterized using the artificial pit technique. As a part of this study, a diffusion model has been developed and employed for calculation of the pit surface concentration of dissolved species during the potential step experiments. For concentrations close to the saturation level the dissolution kinetics are adequately described by a Tafel slope of approximately 57 mV/dec and a current density of 0.5 mA/cm 2 at -300 mV vs. saturated calomel electrode. However, repassivation of the active pit surface occurs when the concentration of the dissolved species drops below 30% of the saturation value. Based on a comparison with relevant literature data, the observed response of the SM stainless steel to localized corrosion is similar to that reported for other high alloyed steels. This result is expected if the dissolution and repassivation kinetics are controlled by the content of Cr, Ni, and Mo in the parent material.