Staged Local Dissolution of Stainless Steel in Chloride Solutions

The paper defines galvanostatic polarization parameters (current density and test duration), to simulate self-dissolution conditions; the results are confirmed by potentiostatic tests. It is shown that under the conditions of self-dissolution simulation, increasing the solution concentration reduces the nucleation rate, while prolonging the pitting development time. Spectral analysis of chronopotentiograms reveals low-frequency potential fluctuations that characterize the nucleation and passivation of pits at the onset of pitting corrosion. The paper describes the basic regularities, observed in the alteration of surface electrochemistry by impedance spectroscopy; such alteration corresponds to the transition from the passive area to the pitting area. The researchers propose optimal electric equivalent circuits to reflect the surface conditions in early nucleation of pits. The paper also proposes an additional pitting resistance criterion, that is, cumulative electric-charge density.

Influence of skirt reinforcement in passive zone on deformation of excavation

In the design of the excavation protection scheme in the soft soil area, it is often necessary to set up cement-soil mixing piles in the passive area. In this way, the stability requirements of the excavation can be met, and the lateral displacement of the retaining pile can be greatly restricted. This paper uses PLAXIS 3D to establish a excavation model in a soft area, and discusses the influence of various parameters of the passive zone mixing pile on the deformation and force of the excavation. Within a certain range, as the cohesive force or secant modulus or reinforcement width or depth of the reinforcement area increases, the lateral displacement and settlement outside the pit will decrease. But when it exceeds a certain range, the decreasing trend becomes very slow. With the increase of the four parameters of the reinforcement zone, bending moments in opposite directions appear below the bottom of the excavation. Moreover, the value of the bending moment is getting larger and larger. Therefore, considering the force, it is not that the wider and deeper the reinforced zone is, the more advantageous is.

Staged Local Dissolution of Stainless Steel in Chloride Solutions

The paper defines galvanostatic polarization parameters (current density and test duration) to simulate self-dissolution conditions; the results are confirmed by potentiostatic tests. It is shown that under the conditions of self-dissolution simulation, increasing the solution concentration reduces the nucleation rate, while prolonging the pitting development time. Spectral analysis of chronopotentiograpms reveals low-frequency potential fluctuations that characterize the nucleation and passivation of pits at the onset of pitting corrosion. The paper describes the basic regularities observed in the alteration of surface electrochemistry by impedance spectroscopy; such alteration corresponds to the transition from the passive area to the pitting area. The researchers propose optimal electric equivalent circuits to reflect the surface conditions in early nucleation of pits. The paper also proposes an additional pitting resistance criterion, that is, cumulative electric-charge density.

Electrolyte Composition for Distinguishing Corrosion Mechanisms in Steel Alloy Screening

The formation and breakdown of passive layers due to pitting corrosion are a major cause of failure of metal structures. The investigation of passivation and pitting corrosion requires two different electrochemical measurements and is therefore a time consuming process. To reduce time in material characterization and to study the interactions of both mechanisms, here, a combined experiment addressing both phenomena is introduced. In the presented electrolyte the different corrosion mechanisms are distinguished and investigated by cyclic voltammograms and polarization scans. The measurements show a passive area, metastable pit growth, and pitting corrosion as well as repassivation. The pitting corrosion is separated from additional dissolution processes and the standard deviation of the corrosion potential is smaller than in other electrolytes. Both passivation and pitting corrosion can be observed in one measurement without additional corrosion attacks. The deviation between different measurements of the same steel is small; this is helpful for the screening of similar materials.

Corrosion monitoring and root cause identification in high solids concentrators

Black liquor high solids (about 80%) concentrators have often been found to suffer from aggressive corrosion. In particular, the first and second effect bodies are susceptible to corrosion attacks resulting in tube leaks and wall thinning, which limit the availability and lifetime of evaporator lines. Corrosion dynamics and construction materials have been studied extensively within the pulp and paper industry to understand the corrosion process. However, it has been challenging to identify root causes for corrosion, which has limited proactive measures to minimize corrosion damage. Corrosion of the first phase concentrator was studied by defining the potential regions for passive area, stress corrosion cracking, pitting corrosion, and general corrosion. This was achieved by using a technique called polarization scan that reveals ranges for the passive area in which the equipment is naturally protected against corrosion. The open circuit potential, also known as corrosion potential, and linear polarization resistance of the metal were monitored online, which allowed for definition of corrosion risks for stainless steel 304L and duplex stainless steels 2205 and SAF 2906. An online temperature measurement added insight to the analysis. A process diagnostics tool was used to identify root causes of the corrosion attacks. Many of the root causes were related to process conditions triggering corrosion. Once the metal surface was activated, it was difficult to repassivate the metal naturally unless a sufficient potential range was reached.