Florent Bocher

Investigation of Crevice Corrosion of AISI 316 Stainless Steel Compared to Ni–Cr–Mo Alloys Using Coupled Multielectrode Arrays

Close-packed coupled multielectrode arrays simulating a planar electrode were used to monitor the anodic current evolution as a function of position during initiation and propagation of crevice corrosion of AISI 316 stainless steel (UNS S31600) and Ni-Cr-Mo alloy 625 (UNS N06625). Scaling laws x 2 crit vs G and x* 2 crit vs G derived from polarization data in simulated crevice solutions guided the implementation of rescaled crevices with greater spatial resolution. x crit and x* crit are the distances from the mouth to the location where the potential reaches two different critical values, and G is the crevice gap. Scaling laws were also used along with anodic polarization data in simulated crevice solution to predict crevice corrosion behavior of alloy 22 (UNS N06022). Crevice corrosion of AISI 316 stainless steel in 0.6 mol/L NaCl at 50°C readily initiated close to the crevice mouth (i.e., x crit ≈ 0) at modest applied potentials (e.g., E app = 0 V SCE ) and spread both inward and outside the crevice with time. Crevice corrosion initiated farther inside the crevice (i.e., x crit is large) and required higher applied potentials (e.g., E app = 50 mV SCE ) in the case of alloy 625. The local crevice current density increased dramatically over a short period of time to reach a limiting value in the case of AISI 316; while metastable dissolution behavior over a large area was observed for alloy 625. The ramification of the larger critical depth for Ni-Cr-Mo alloys toward crevice corrosion susceptibility in the case of crevice formers of finite length is discussed. Crevice corrosion shifts to the mouth of the crevice for the less corrosion-resistant materials in crevice solutions saturated in metal salts but remains confined at a distance x crit for alloy 625 under the conditions tested.

Prediction of Critical Crevice Potentials for Ni-Cr-Mo Alloys in Simulated Crevice Solutions as a Function of Molybdenum Content

Abstract Critical potentials for crevice corrosion initiation were predicted for Ni-22Cr-XMo alloys (X=0,3, 6, 9, 13%), Alloy 625 (UNS N06625), and Alloy 22 (UNS N06022) based on electrochemical ox...

Coupled Multielectrode Investigation of Crevice Corrosion of AISI 316 Stainless Steel

Close packed coupled multielectrode arrays simulating a planar electrode were used to measure the current evolution as a function of position during initiation and propagation of crevice corrosion of AISI 316 stainless steel. Scaling laws derived from polarization data guided the implementation of rescaled crevices providing spatial resolution. Crevice corrosion of AISI 316 stainless steel in 0.6 M NaCI at 50°C was found to initiate close to the crevice mouth and to spread inward and outward with time. The local crevice current density increased dramatically over a short period to reach a limiting value.

Localized Corrosion Resistance of Fe-Cr-Mo-W-B-C Bulk Metallic Glasses Containing Mn+Si or Y in Neutral and Acidified Chloride Solutions

Abstract The localized corrosion properties of a series of iron-based metallic glasses containing either the elements Fe-Cr-Mn-Mo-W-B-C-Si or Fe-Cr-Mo-W-B-C-Y have been studied in near-neutral pH, ...

Stifling of Crevice Corrosion and Repassivation: Cathode Area Versus Controlled Potential Decreases Assessed with a Coupled Multi-Electrode Array

The effects of limited remote cathode area on crevice corrosion propagation, repassivation, and anode site reorganization were investigated on AISI 316 stainless steel (UNS S31600) in 0.6 M NaCl at 50°C. Both multiple crevice assemblies and rescaled coupled multi-electrode arrays were utilized. Potentiostatically activated crevices were subjected to conditions that limited propagation by either: (i) stepping the potential downward below the repassivation potential, (ii) performing a downward scan of the potential from high potential, or (iii) decreasing the area of a galvanically coupled platinum cathode situated outside the crevice. In the first two cases, repassivation occurred when the potential reached the lower statistical limit of the repassivation potential measured on creviced specimens in a downward scan. During the galvanically coupled test, repassivation occurred when the galvanic cathodic current supplied became lower than the current required to maintain a couple potential equal to the repass...

Coupled Multi-Electrode Investigation of Crevice Corrosion of 316 Stainless Steel and NiCrMo Alloy 625

Crevice corrosion is currently mostly studied using either one of two techniques depending on the information desired. The first method involves two multicrevice formers or washers fastened on both sides of a sample plate. This technique provides exposure information regarding the severity of crevice corrosion (depth, position, frequency of attack) but delivers little or no electrochemical information. The second method involves the potentiodynamic or potentiostatic study of an uncreviced sample in a model crevice solution or under a crevice former in aggressive solution where crevice corrosion may initiate and propagate and global current is recorded. However, crevice corrosion initiation and propagation behavior is highly dependent on exact position in the crevice over time. The distance from the crevice mouth will affect the solution composition, the pH, the ohmic potential drop and the true potential in the crevice. Coupled multi-electrode arrays (MEA) were used to study crevice corrosion in order to take in account spatial and temporal evolution of electrochemistry simultaneously. Scaling laws were used to rescale the crevice geometry while keeping the corrosion electrochemical properties equivalent to that of a natural crevice at a smaller length scale. one of the advantages was to be able to use commercial alloys available as wires electrode and, in the case of MEA, to spread the crevice corrosion over many individual electrodes so each one of them will have a near homogeneous electrochemical behavior. The initial step was to obtain anodic polarization curves for the relevant material in acid chloride solution which simulated the crevice electrolyte. using the software Crevicer{trademark}, the potential distribution inside the crevice as a function of the distance from the crevice mouth was determined for various crevice gaps and applied potentials, assuming constant chemistry throughout the crevice. The crevice corrosion initiation location x{sub crit} is the position where the potential drops to E{sub Flade}. Figure 1 illustrates the resulting x{sub crit} vs. G scaling laws for 316 Stainless Steel in 1 M HCl at 50 C. The coupled multi-wire array is composed of one hundred identical 316 Stainless Steel wires in a five by twenty formation inserted in a groove of a 316 Stainless Steel rod such that the ends of the wires are flush mounted with the rod. The 100 wires are coupled electrically through in-line zero resistance ammeters. The diameter of the wires (250 {micro}m) was chosen so that x{sub crit} (critical initiation distance from the crevice mouth) and the expected zone of crevice corrosion (predicted from the scaling law) would be larger than the radius of a single wire. The array created a flush mounted planar electrode with the surface/volume ratio obtained in planar crevices. The observation of the current evolution as a function of position inside and outside the crevice as function of time was made possible as illustrated in Figure 2 in 0.6 M NaCl at 50 C.