Pitting Corrosion Characteristics Research Articles

Pitting corrosion characteristics of sintered Type 316 L stainless steel: relationship between pores and MnS

In Type 316 L stainless steel fabricated from gas-atomized powder via spark plasma sintering, lack-of-fusion pores and MnS inclusions were identified as possible pitting initiation sites. Through potentiodynamic polarization with different working electrode areas, the distribution density of the identified pit initiation sites was compared with that of sites found on wrought Type 316 L stainless steel. Surface observations of the sintered Type 316 L after polarization suggest that pitting corrosion was initiated at a location where both MnS and pores existed. By reducing the porosity and removing MnS, the roles of pores and MnS inclusions in the initiation of pitting corrosion were investigated.

Study on metal corrosion behavior of heat-affected zone of oil pipeline

Due to the influence of welding technology, a series of non-uniform and continuous heat-affected zones formed by welding seams is the weakest link of pipeline steel. Compared with the X70 steel, the heat-affected area is in the form of coarse acicular and massive ferrite, granular bainite, and a small amount of pearlite, with weak strength and corrosion resistance. Therefore, this paper simulated the heat-affected zone of the high-strength steel welding seam by the Gleeble 3500 thermal/force simulation testing machine for two heat cycles. Taking Shengli crude oil as the experimental medium, the metal corrosion morphology of heat-affected zones at different temperatures and transmission rates during hot oil transportation was analyzed through immersion experiment and corrosion morphology characterization. The results show that the increase in temperature and flow rate will increase the overall corrosion rate of the metal in the heat-affected area. In the range of 30∼50°C, pitting corrosion was the main corrosion feature of the metal, and in the range of 50∼70°C, the corrosion morphology of the metal changed from pitting corrosion characteristics to comprehensive corrosion characteristics. In the range of the flow rate studied (1∼4 m/s), the metal in the heat-affected area was mainly the overall corrosion rate, and the metal surface showed the erosion-corrosion characteristics along the flow rate direction.

Axial compressive behavior of corroded H-shaped steel columns

The unpredictability of corrosion in steel structures, especially in H-section columns, is a topic that has received limited research attention. Using Monte Carlo simulation (MCS) and finite element analysis (FEA), this study investigates the effect of random pitting corrosion on H-section steel columns' ultimate bearing capacity under axial compression. In this study, MCS was employed to address the random distribution of pitting corrosion. The reliability of MCS and FEA was validated through existing literature on compression tests of H-shaped steel columns. To comprehensively assess the detrimental effects of pitting corrosion, a total of 3650 models of H-shaped columns, each exhibiting different pitting corrosion characteristics, were subjected to analysis. These models incorporated three corrosion parameters (volume loss rate, size, and depth) and two geometric parameters (slenderness and section size). A nonlinear buckling analysis was carried out to investigate the ultimate bearing capacity of the columns. The findings indicate that a volume loss rate of 20% can cause a decrease in the column's ultimate bearing capacity by approximately 50%. Furthermore, the study reveals that at equal volume loss rates, corrosion depth and slenderness significantly influence the reduction factor, while corrosion size and section size exert a minimal impact. As a result, this paper introduces a probabilistic assessment method for estimating the reduction factor in ultimate bearing capacity for H-section steel columns. Notably, with every 10% increase in the volume loss rate, the mean reduction factor in the ultimate bearing capacity decreases by approximately 0.12.

Research on pitting corrosion characteristics of X90 steel based on acoustic emission and electrochemistry methods

The X90 pipeline steel pipe is expectedto become the standard steel in future pipeline construction due to its high transmission efficiency and lower cost. However, little study has been conducted on corrosion on-line monitoring of X90 steel. To investigate the pitting development of X90 steel, a combined electrochemical device and acoustic emission (AE) system was set up in this work. The results reveal that the pitting process can be divided into three stages: activation response and passive film rupture, and corrosion pit propagation, and pitting reaction. In addition, the corrosion rate of metal is quite high during the activation reaction and passivation film rupture stage, and the characteristic parameters of the AE signal are very large. In the frequency domain, the frequency range is mostly centered between 100 and 200 kHz, with a peak frequency of about 150 kHz. The corrosion pit propagation stage is the transition stage from metal oxidation to metal pitting reaction. The activity of the signal is low, and the characteristic signal is diminished, and the frequency domain characteristics are comparable to the preceding stage. The signal activity rises, the total signal intensity increases, and several signals exceeding 55 dB arise during the pitting response stage.

Microstructure and Pitting Corrosion Characteristics of Tig Welded Joints of Super 304HCu Austenitic Stainless Steel

Abstract Super 304HCu is an advanced ultra-super critical (A-USC) boiler grade austenitic stainless steel with the distinct addition of 3 wt.-% of Copper. A-USC power plants intended to operate in chloride rich environments (sea shore, feed water residues, etc.) are susceptible to chloride assisted corrosion failures. In this study, the pitting corrosion behaviour of the Super 304HCu parent material and tungsten inert gas weld joints was studied using a potentiodynamic cyclic polarization test in 3.5 % NaCl solution at three different pH levels (pH = 3, pH = 7, and pH = 11). The Epit values of the parent material is found to be much nobler than that of the weld joints. The micrographs of the pitted weld joints and the oxalic acid etched structure of Super 304HCu joints are presented. From the micrographs it is revealed that the heat affected zone is the most susceptible region to pitting corrosion.

Study on the Influence of Non-Metallic Inclusions on the Pitting Corrosion of API 5L X60 Steel

The most economical way to move liquids and gaseous hydrocarbons is by using pipelines. According to several international organizations and oil companies, the use of fossil fuels will continue in the following decades. For this reason, it is important to continue studying different corrosion mechanisms and their origins. One of the mechanisms that provoke small leaks, affecting pipeline hermeticity, is pitting corrosion. It is well-known that non-metallic inclusion dissolution can trigger pit nucleation. As pitting corrosion is recognized to be random in nature, it is also interesting to study the random nature of the inclusions present in API 5L X60 steel. Probability distributions commonly used to describe pitting corrosion characteristics are appropriate for studying inclusion characteristics. The size of inclusions plays a key role in pit nucleation because small inclusions tend to generate more defects, especially when these inclusions are compounds of MnS, and the steel is immersed in a corrosive solution. The results of this research work show that there is a close relationship between the random nature of pitting corrosion and inclusions.

Failure analysis of a high strength Cr-containing tube used in an oil well

With the development of oil and gas resources, the service condition of tube steel becomes more and more severe in oilfields, leading to a large number of corrosion failure cases in actual production. The systematic analysis of the failed parts can help to find failure reasons and propose protection methods. In this paper, the failure analysis of a high-strength tube fractured in a real oilfield was carried out by inspecting the basic properties and corrosion characteristics of the steel. SEM, EDS and XRD were used to analyze the chemical compositions of the products on the surface and around the crack tip. Results indicated that the failure of the tubing steel was due to the stress corrosion cracking under the effects of Cl-, sulfide and stress. Intergranular and pitting corrosion characteristics were also discovered on the failed tube. Microcracks started on the inner wall and propagated to the outer wall. Cl- largely aggregated at both sides of the crack tip, providing a driving force for crack propagation.

Understanding the local pitting corrosion characteristics of carbon steel in CO2 corrosion environment using artificially machined pits

Carbon steel remains the most commonly used material in CO2 – containing oilfield, and other energy applications. Pitting corrosion is a prominent form of corrosion attack on carbon steel, and linked to the formation of non – protective iron carbonate (FeCO3) films and/or their breakdown. The conditions for local breakdown of FeCO3, and other fundamental aspects of pitting corrosion are still not clearly understood; particularly in relation to the evolution of the local chemistry within active pits. Local distribution of corrosion activities/species is likely to influence FeCO3 formation; evolution and properties to support and/or impede pit propagation. This study investigates the local corrosion environment within an artificially machined pits to understand the local pitting corrosion behaviour. It focuses on the local evolution of FeCO3 and pitting corrosion. Pits with specific geometry on X65 carbon steel samples are exposed to two different environments: pH of 4 and 5.9 for 168 h. Tests were performed at atmospheric pressure and 60 °C in 1 M NaCl solution. Linear polarization technique was implemented in combination with a suite of post-experiment surface analysis: Scanning Electron Microscopy, X-ray diffraction, 3D-profilometry and Raman spectroscopy for assessing overall corrosion rate, localised corrosion products and pitting characteristics. Results show that at both pH levels, more crystalline FeCO3 was formed within the pits than at the top surfaces. The size and compactness of FeCO3 decrease from the base of the pits towards the top surfaces, which correlates with the extent of pitting corrosion within the pit and the spatial variation in the local chemistry.

On the Importance of Geometry in Open Bipolar Electrochemistry Configurations for Corrosion Studies

This work aims to optimize cell geometry with finite element modeling to ameliorate open Bipolar electrochemistry (BPE) and split BPE setups, increase the faradaic current through the bipolar electrode to trigger localized corrosion on the anodic region, and study the corrosion behavior of anodic films when activated as bipolar electrodes under thermostatic condition.The advent of Bipolar electrochemistry (BPE) stems from a series of investigations on fluidized bed electrodes conducted by Fleischmann et al. in the 1970s.[1] Since then, and mainly in the recent decade, BPE has been profoundly scrutinized and exploited in disparate fields such as electrodeposition[2,3], synthesis of Janus particles, propulsion of microparticles, corrosion of stainless steel[4,5], anodizing[6], biosensors, and water treatment. Additionally, it has been studied in miscellaneous formats including split BPE, 2D BPE, and array BPE. Fundamentally, BPE is performed by applying an electric field between two inducing electrodes through an electrolytic medium in which an electronic conductor is immersed. The electronic conductor is indirectly polarized such that one end becomes anodic and the other cathodic thus creating two poles of charge.Due to lack of direct contact to the bipolar electrode, direct monitoring of the current and potential of the bipolar electrode is not viable. However, indirect measurement of current and potential through the integration of BPE with electrogenerated chemiluminescence (ECL), surface plasmon resonance imaging (SPRi), and scanning vibrating electrode technique (SVET) have been proven feasible. In studies that coupled BPE and ECL as well as in corrosion studies of a stainless-steel bipolar electrode, an apparent curvature of the equipotential lines, specifically near the extremities of the bipolar electrode, is noticed[7,8], although it has not been addressed to date. This nonlinearity of potential can be related to the non-uniform electric field in the electrolyte and can be precluded via manipulation of cell geometry.The major benefit of using BPE for corrosion studies compared to traditional three-electrode techniques with direct polarization is the presence of a continuum of applied potentials distributed along the length of the bipolar electrode in the direction of the electric field. The distribution of potential results in distinct corrosion behaviors that may be analyzed along the length of the metal. Nevertheless, the challenge is to configure the experimental setup in a way that promotes a one-dimensional distribution of applied potential on a 2d surface while ensuring the polarization is high enough to produce the necessary corrosion response. Doing so allows one to study pitting characteristics such as pit initiation rates and distribution as well as pit growth rate from post-analysis of pit size distributions. References R. Backhurst, J. M. Coulson, F. Goodridge, R. E. Plimley, and M. Fleischmann. A preliminary investigation of fluidized bed electrodes. Journal of the Electrochemical Society, 116 197 (11):1600, 1969Braun, T. M., and D. T. Schwartz. "Localized electrodeposition and patterning using bipolar electrochemistry." Journal of The Electrochemical Society162, no. 4 (2015): D180.Rahul Dhopeshwarkar, Dzmitry Hlushkou, Mark Nguyen, Ulrich Tallarek, and Richard M. Crooks. Electrokinetics in microfluidic channels containing a floating electrode. Journal of the American Chemical Society, 130(32):10480–10481, 2008Yiqi Zhou and Dirk Lars Engelberg. Application of a modified bi-polar electrochemistry approach to determine pitting corrosion characteristics. Electrochemistry Communications, 220 93:158–161, 2018.Sara Munktell, Leif Nyholm, and Fredrik Bjorefors. Towards high throughput corrosion screening using arrays of bipolar electrodes. Journal of Electroanalytical Chemistry, 747: 239 77–82, 2015.Ryo Takeuchi and Hidetaka Asoh. Effects of size and position of an unconnected aluminum electrode on bipolar anodization in an AC electric field. Scientific reports, 11(1):1–7, 2021Vera Eßmann, Jan Clausmeyer, and Wolfgang Schuhmann. Alternating current-bipolar electrochemistry. Electrochemistry Communications, 75:82–85, 2017Gwendoline Tisserant, Zahra Fattah, Ce´dric Ayela, Je´roˆme Roche, Bernard Plano, Dodzi Zigah, Bertrand Goudeau, Alexander Kuhn, and Laurent Bouffier. Generation of metal composition gradients by means of bipolar electrodeposition. Electrochimica Acta, 179:276–281, 2015. Figure 1

Estimating Pitting Corrosion Depth and Density on Carbon Steel (C-4130) using Artificial Neural Networks

The purpose of this research is to investigate the impact of corrosive environment (corrosive ferric chloride of 1, 2, 5, 6% wt. at room temperature), immersion period of (48, 72, 96, 120, 144 hours), and surface roughness on pitting corrosion characteristics and use the data to build an artificial neural network and test its ability to predict the depth and intensity of pitting corrosion in a variety of conditions. Pit density and depth were calculated using a pitting corrosion test on carbon steel (C-4130). Pitting corrosion experimental tests were used to develop artificial neural network (ANN) models for predicting pitting corrosion characteristics. It was found that artificial neural network models were shown to be quite effective; the results were validated by the experimental agreement with those acquired from laboratory tests. Specifically, the correlation coefficient, R = 0.9944.

Numerical analysis of the correlation between the pitting severity and surface roughness of corroded specimens

ABSTRACT Repeated wet–dry cycle exposure to seawater during ballasting processes hastens the surface corrosion rate. Moreover, the larger volumetric changes of corroded ballast tanks generate lower pitting severity. This paper models the pitting severity of corroded ballast tanks of varying roughness and volumes. Seven rectangular finite elements models with Gaussian rough surfaces are examined. The surface roughness modelling is analyzed with correlation among corrosion-statistical parameters at various corroded specimen volume changes. Additionally, the paper elaborates the severity of pitting corrosion characteristics using the pitting factor and the relationship between the maximum and average pit depth. The pitting severity – volumetric changes scenario investigates the model’s stress distribution, showing that the greater change in volume and lower pitting severity tend to have a lower stress distribution, which is randomly concentrated on the larger area. Comparison of the theoretical results with physical test data using 3D laser scans indicates a close match.

Iron sulphide formation and interaction with corrosion inhibitor in H2S-containing environments

Corrosion of carbon steel in H2S-containing environments poses serious challenges to operations in oilfield and geothermal applications. Carbon steels exposed to H2S-containing environments are often susceptible to pitting and uniform corrosion, and linked to the properties of iron sulphide (FeS) layers that forms at the corroding interface. This paper investigates the corrosion characteristics of carbon steel in H2S-containing environments focussing on the early stage kinetics of FeS formation and its interaction with corrosion inhibitors (CI). Experiments were conducted in 3.5 and 5.8 wt% NaCl solution at 80 °C in 10% H2S-90% CO2-containing environments. In-situ electrochemical responses were measured using the linear polarisation resistance (LPR) technique. This was combined with post-experiment surface analysis; scanning electron microscopy (SEM) and X-ray diffraction (XRD) to investigate the nature and morphology of formed FeS. 3D surface profilometry was used to investigate the pitting corrosion characteristics of carbon steel caused by FeS interaction with CI. The results show a fast kinetics of FeS formation by direct reduction of H2S(aq) with a distinct and easily identifiable morphology, and evidence of minimum level of ferrite dissolution. The early stages of FeS formation and its interaction with CI have a strong influence on the overall corrosion characteristics of carbon steel. A dose of 30 ppm of a commercial corrosion inhibitor (CI); salts of nitrogenous molecules with a fatty acid group, at the corrosion interface induced a competition for surface absorption between CI and emerging FeS. Over the 48 h duration of this test, the FeS formation process was delayed and the mechanisms of its formation quickly became the main driver of pitting corrosion. The amount of CI dosed in this study was not able to prevent FeS-induced pitting corrosion attack on the surface.

Numerical simulation and experimental verification of random pitting corrosion characteristics

Corrosion is the most common type of damage to the hull structures of ships, and pitting corrosion damage has garnered the attention of researchers owing to its complexity and randomness. This study investigated the effects of random pitting on the performance of ship hull plates by developing Python script and proposing a numerical simulation method for establishing the randomness of pitting (form and distribution). The applicability and reliability of the proposed method were then verified through a pitting test. Finally, under the same degree of pitting damage condition, the influences of different random pitting patterns on the tensile properties of unstiffened plates and the ultimate strength of stiffened plates were investigated. The method presented in this paper provides technical support and establishes a foundation for the investigation of the influence of pitting randomness on the fatigue life of steel plate structures and the development of methods for the intelligent identification of steel plate pitting damage.

Application of a modified bi-polar electrochemistry approach to determine pitting corrosion characteristics

The application of bi-polar electrochemistry produces a linear potential gradient between two feeder electrodes, allowing the full spectrum of anodic to cathodic reaction kinetics to be controlled. A modified bi-polar approach is introduced, by superimposing a constant electrochemical potential on the potential gradient, thereby controlling the location and spatial distribution of anodic to cathodic reactions along the exposed sample surface. Application of this approach is demonstrated by controlling the extent of pitting corrosion in austenitic stainless steel as a function of the applied potential.

A Study of the Pitting and Uniform Corrosion Characteristics of X65 Carbon Steel in Different H2S-CO2-Containing Environments

There have been increasing concerns related to the challenges posed by hydrogen sulfide (H2S) corrosion to the integrity of oilfield pipeline steels. In environments containing variable quantities of both carbon dioxide (CO2) and H2S gas, the corrosion behavior of carbon steel can be particularly complex. There is still no universal understanding of the changes in the mechanisms, sequence of electrochemical reactions and impact on the integrity of carbon steel materials as a result of changes in H2S-CO2 gas ratio. The film formation process, film characteristics, and morphology in CO2- and H2S-containing systems are also known to be different depending upon the environmental and physical conditions and this influences the rates of both general and pitting corrosion. Questions still remain as to how the combined presence of CO2 and H2S gases at different partial pressure ratios influence the corrosion mechanisms, as well as initiation and propagation of surface pits. This paper presents an investigation into the overall (i.e., general and pitting) corrosion behavior of carbon steel in CO2-H2S-containing environments. The work explores the impact of changes in ratios of CO2 and H2S partial pressures at both 30°C and 80°C in a 3.5 wt% NaCl solution. All experiments are performed at atmospheric pressure, while H2S gas content is varied at 0 ppm (0 mol%), 100 ppm (0.01 mol%), 1,000 ppm (0.1 mol%), 10,000 ppm (1 mol%), and 100,000 ppm (10 mol%) in H2S-CO2 corrosion environments. Corrosion film properties and morphology are studied through a combination of scanning electron microscopy and x-ray diffraction. The results show that the morphology and composition of iron sulfide formed changes with H2S gas concentration because of the continuous interaction of the corrosion interface with the corrosion media even in the presence of initially formed FeS (mainly mackinawite). This often leads to the formation of a different morphology of mackinawite as well as different polymorphs of FeS. This also has the impact of either increasing or decreasing the uniform corrosion rate at low and higher concentration of H2S gas depending on the temperature. Pitting corrosion is also evaluated after 168 h to determine the impact of increasing H2S content on the extent and morphology of pitting corrosion attack. The results from the pitting corrosion investigation show that increased and severe pitting corrosion attack occurs at higher H2S concentration and temperature. The morphology of pitting corrosion attack is also linked to the changes in the H2S content with an indication of a critical concentration range at which the nature of attack changes from narrow and small diameter pits to severe localized attack. The critical concentration threshold for such transition is shown in this study to reduce with increasing temperature.

Corrosion of anchorage head system of post‐tensioned prestressed concrete structures under chloride environment

Corrosion of anchorage head system may lead to severe structural failure. To understand the characteristics of corrosion and the risks of anchoring failure, 11 post‐tensioned prestressed concrete specimens with single‐hole anchorage‐plate system sealed with postcast concrete contaminated by NaCl were fabricated and then corroded for 8 months. By periodically monitoring corrosion current density and breaking the specimens to detect mass loss, the time‐varying law of corrosion rate and the influences of chloride concentration and cover layer depth on corrosion rate were found. The mean corrosion rate of each component of anchorage head system varies with effective prestress level in a light growing trend with approximate linear relationship. The plates were corroded most severely and manifested relatively full and uniform corrosion characteristics, whereas the barrels and wedges were corroded slightly and exhibited relatively local and pitting corrosion characteristics. The average corrosion rate of the plates is 50 times and 80 times higher than that of the barrels and wedges, respectively. The interfaces of the contacted components were hardly corroded. Finally, the corrosion risk of the anchorage head system was analyzed.

Cluster analysis of acoustic emission signals in pitting corrosion of low carbon steel

The pitting corrosion characteristics of low carbon steel specimens are studied by acoustic emission (AE) and electrochemical techniques, in a 3.0 wt.% NaCl solution acidified to pH 2.0. The acoustic emission signals generated by pitting corrosion are classified based on multiple acoustic emission parameters using K‐means clustering algorithm, then each classified signals are analyzed by acoustic emission parameters correlation plot and distribution with time. Furthermore, each acoustic source characteristics is extracted using Gabor wavelet transform (WT) in the time and frequency domain. An error back propagation (BP) artificial neural network (ANN) is trained according to the classified signals, so as to successfully identify the acoustic emission signals from parallel experiments. Experimental results show that the hydrogen bubble activation, oxidized film rupture and pit growth are typical acoustic emission sources in pitting corrosion process, which can be effectively classified by cluster analysis and recognized by back propagation neural network. The data gathered from laboratory tests combined with the real data from acoustic emission on‐line storage tank floor inspection can help to evaluate the bottom corrosion severity and interpreter the corrosion source, further to make the on‐site testing more reliable and reduce the risk.

Effect of deformation route on the development of low CN Fe-20%Cr alloy by Equal Channel Angular Pressing

The effect of deformation routes on the microstructure, mechanical, and electrochemical properties of low CN Fe-20%Cr alloys by equal channel angular pressing (ECAP) has been investigated in detail focusing on the anisotropy of the microstructure. This alloy is pressed at 423K up to eight passes via the so-called routes A, Bc and C. The continuous refinement of the microstructure is sustained by ECAP until the sub-grain range. However, the degree of anisotropy of microstructural development was different among the three deformation routes. Materials processed by Route Bc exhibited a comparable micro-hardness value in three orthogonal planes than those processed by routes A and C. Pitting corrosion characteristics of the ECAP processed sample were investigated using an electrochemical potentiodynamic test. The increased pitting potential along with an increased number passes of ECAP were explained by enhanced protective passive layer of ultrafine grain structure, as compared to the coarse grain counterpart.

Study of the correlation between pitting corrosion and the component ratio of the dual phase in duplex stainless steel welds

Three duplex stainless steel weldments were produced by changing the chromium element to study the correlation between the pitting corrosion characteristics and the component ratio of the dual phase. The pit morphologies showed that metastable pits were generated at a lower pitting resistance equivalent number (PREN) phase. The secondary austenite phases seemed to serve as a path for the corrosive environment regardless of the ferrite number (FN). There is some discrepancy between the measured values (pitting potential (Ep) through polarization test) and expected values (sequence ranked by PREN of weaker phase) in 1moll−1 NaCl solution at 60°C.

Prediction of Pitting Corrosion Characteristics using Artificial Neural Networks

Precorroded steel A-106 B specimens were prepared at different surface roughness. These specimens were immersed in corrosive ferric chloride solution in different concentrations (1.5, 3.0, 4.5, 6.0% wt.) at specified durations to initiate primarily the pitting corrosion. The corrosion pits distribution depend on the corrosive concentration, degree of surface roughness, and immersion duration. The pits were characterized using metallurgical microscope. Also, The pitting characteristics aimed to be predicted by “Artificial Neural Networks” (ANNs). The results obtained of pit quantification by ANNs predictions are shown to be agreed well against experimental values. i.e. R2=0.9839