Pit Depth Research Articles

Fracture resistance of naturally corroded steel after service for 128 years

The fracture resistance of steel in aged structures after long-time service can be significantly degraded by corrosion, which can lead to catastrophic failures of the structure. This paper aims to experimentally investigate the fracture characteristics of naturally corroded steel cut from a bridge girder after 128 years’ service. Mechanical tests and microstructural analyses are conducted on the specimens with various levels of corrosion and the relationship between fracture toughness reduction and corrosion level is quantitatively investigated. The fracture mechanism of the corroded steel is critically analysed and discussed. It is found from the test results that steel subjected to pitting corrosion has strong negative correlation with the local corrosion levels in front of the pre-cracks of the specimens, but is seldom related to the overall corrosion levels. The uneven corroded surfaces of specimens lead to significant differences in the J-R curves of the specimens with a similar range of average pit depth. It is also found from the fractography analyses that less ductile fracture characteristics are exhibited near the severe corrosion pits, which limits the fracture resistance of corroded steel. The findings presented in this paper can contribute to the development of optimal maintenance strategies of aged steel structures for engineers and asset managers.

Atomic simulation of textured silicon carbide surface ultra-precision polishing

In view of increasing accuracy requirements and difficult machining characteristics of silicon carbide materials, this paper proposes new machining method with ultra-high precision. Based on improvement of ultra-precision machining quality by textured surface, specific nano texture was machined on silicon carbide surface. Effects of different texture parameters on polishing force, polishing temperature, potential energy, dislocation, stress and friction coefficient were analyzed. Two typical textures (grooves and pits) with different sizes were compared. Simulation results show that surface morphology, polishing force and friction coefficient are improved with the increase in groove depth and pit depth. The smaller the groove spacing, the better the polishing quality and polishing behavior. In addition, groove texture can effectively inhibit the growth of dislocations and defect atoms during polishing. Compared with non-textured surface, textured silicon carbide surface can improve polishing conditions. It is found that groove texture has more beneficial effect on polishing quality than pit texture with the same size.

High stress corrosion cracking resistance of in-situ nanoparticle strengthened steel

Stress corrosion cracking (SCC) is extremely detrimental to the long-term applications of high-strength low-alloy steels. In this work, the critical effects of the dimension and morphology of the non-metallic inclusions on the SCC susceptibility and pitting corrosion were investigated. With the trace-element regional supply method, the inclusions are transformed from the detrimental sharp-edged (Ti, V)N and enormous MnS into globular or elliptical Al2O3 and multicomponent inclusions with small dimensions (3.41 ± 2.36 μm) and high equivalent shape factor (0.93 ± 0.02) in the in-situ nanoparticles strengthened steel. As a result, the corrosion current, depth and diameter of pits, and roughness of the surface were reduced with suppression of pitting corrosion. The superior SCC resistance in the in-situ nanoparticles strengthened steel was obtained by inclusion refinement. The strategy of inclusion refinement by in-situ nanoparticles is beneficial for designing SCC resistant steels.

Enhanced Bio-corrosion Resistance by Cu Alloying in a Micro-alloyed Pipeline Steel

On the composition base of commercial X65 grade pipeline steels, a Cu modified pipeline steel was designed to show improved resistance to microbially induced corrosion (MIC). The mechanical properties of the Cu-added steel and its corrosion behavior in a soil solution inoculated with sulfate-reducing bacteria (SRB) were investigated in this work. The results demonstrated that Cu-added steel exhibits a good combination of strength and toughness. Cu ions released from the Cu-added steel could effectively kill the SRB attaching on the steel surface, thus evidently decreased the pit depth and diameter of Cu-added steel. Furthermore, during the long-term immersion, the Cu-rich film formed by the enrichment of Cu in the corrosion product layer on the steel surface could also contribute to the improvement of the bio-corrosion resistance of Cu-added steel.

A discussion of “optimisation of compressed earth blocks (CEBs) using natural origin materials: A systematic literature review”

On 11 October 2021, this journal published a review article entitled “Optimisation of Compressed Earth Blocks (CEBs) using natural origin materials: A systematic literature review” [1]. The article made a very interesting state of the art review which allows the advancement of the knowledge on the improvement of the performance of CEBs. However, the present discussion points out that the review failed to recommend to take into consideration the reactivity, in addition to the parameters of texture and plasticity, for the selection of earth for the production of optimised CEBs. The review also simplified the relation between the thermal conductivity and density of CEBs, to a linear correlation. Moreover, the correlation between the compressive strength and bulk density is better approached by an exponential law rather than the linear law as was claimed in the review. Finally, the review should have recommended the consideration of eroded area, in addition to the depth of erosion pit, for the assessment of the erosion resistance of CEBs.

Understanding the nature of passivation film formed during corrosion of Fe39Mn20Co20Cr15Si5Al1 high entropy alloy in 3.5 wt% NaCl solution

In metallic materials, the nature of passivation film plays an important role in governing corrosion behavior. The present work focuses on a detailed analysis of the passivation film characteristics of a transformation induced plasticity Fe39Mn20Co20Cr15Si5Al1 (at%) high entropy alloy (HEA) in 3.5 wt% NaCl solution at room temperature. The characteristics of the passivation film were assessed using a potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). The microstructural analysis of the alloy achieved using electron backscattered diffraction revealed that it consisted of two different phases: γ phase (face-centred cubic crystal) and ε (hexagonal closed pack), with the area fraction of ε phase being 96.5%. The electrochemical experiments showed that the HEA maintained excellent uniform corrosion resistance but low pitting corrosion resistance. The scanning electron microscopy revealed deep pits covered with perforated layers, and the average pit size and pit depth was determined to be 202.8 µm and 168 µm, respectively. The EIS revealed a bilayer type of passivation film formations at different voltages. For the passivation film grown at −0.1 V, the upper layer film thickness was 2.08 nm and the inner layer film thickness was 3.14 nm. For the passivation film grown at −0.05 V, the upper and inner film thicknesses were 1.78 nm and 3.10 nm. The passivation film resistance was found to be one order of magnitude higher for the passivation films grown at −0.1 V and −0.05 V than that for the naturally grown passivation film. The XPS of the sample that corroded during the potentiodynamic polarization test revealed that the passive layer contained Fe, Mn, Co, Cr, Si, and O elements as metal oxides and hydroxides with Mn and Cr based chemical species present as dominant species. Their oxidation states were estimated to be present as Fe2+, Fe3+, Mn3+, Co2+, Cr3+, Si4+, O2-, and OH1- along with their corresponding metallic states. According to the proposed corrosion mechanism, a bilayer type of passivation film forms on the alloy. The film’s upper layer is rich in Mn and Cr and the inner layer is devoid of Mn and Cr. The detection of two particles in the same pit with two different chemical compositions seems to corroborate the formation of a bilayer passivation film and its chemical compositions.

Assessment of ablation damage on quartz ceramics through experiment and 3D modelling considering a dynamic heat source

The effects of irradiation time (IT), laser power (LP), and spot diameter (SD) on the damage caused to quartz ceramics under continuous-wave laser irradiation were investigated through an orthogonal experiment. The experimental results show that the LP has the dominant effect on the depth of an ablation pit, while the SD has the greatest impact on the diameter of the ablation centre. The diameter and depth of the ablation pit were both positively correlated to the irradiation energy. The bubbles and molten silica transition layer affected the laser beam's reflection and transmission properties, leading to the incident laser beam scattering into the entire ablation pit and forming an elliptical ablation pit. Furthermore, a 3D finite element (FE) model considering a dynamic heat source was developed to simulate the laser damage process. The shape and dimension of the ablation pit predicted by the FE model were consistent with those obtained through the experiment, demonstrating the effectiveness and rationality of the model. The FE analysis results show that the different ablation rates in the radial and depth directions significantly influence the morphology of the ablation pits. The temperature gradient in the transition region increases while the thickness of the transition region decreases as the LP increases. This indicates that a large LP will lead to greater thermal stress in this area and result in more microcracks.

Experimental study of bed morphology evolution under two-dimensional dam-break flow

The present study discusses the evolution of bed morphology under 2D dam-break flow by conducting a set of laboratory experiments. The experiments were conducted in a 1.6 m × 28 m × 1.0 m glass flume with non-uniform fly ash as the bed material. Two scenarios were designed: no inflow (scenario 1) and nearly constant water level (scenario 2) in the upstream reservoir. During the experiment, the water levels were measured by pressure sensors which were buried under the sediment layer, and the bed morphology was measured by an ultrasonic ranging system. The results showed that: (1) in scenario 1, the range and depth of the scour pit continued to increase, but the location of the deepest scour point did not change significantly; (2) in scenario 2, the depth and range of scour increased after the dam break, but the growth rate slowed down obviously after t = 15 min. The data can be employed to understand the bed morphology evolution under a dam-break flow, validate numerical approaches, and test geomorphic flood models.

Fatigue life assessment of high-strength steel wires: Beach marks test and numerical investigation

High-strength steel wires are widely used in large-span bridges. Fatigue damage of steel wires is becoming more and more prominent under adverse environment and repeated load. This paper performed the fatigue crack growth rate tests of high strength steel wires under different stress ratios. The striated fracture morphology was obtained by stepwise fatigue loading method. The fatigue crack growth rate of steel wire was determined by measuring fracture stripe width by optical microscope. The experimental curves of fatigue crack growth rate versus stress intensity factor range under various stress ratios were obtained. The fracture morphology of steel wires after fatigue was observed by scanning electron microscopy. The characterization parameters of fatigue crack growth and critical fracture required for numerical simulation were obtained based on experimental results and statistical method. Following that, a numerical fatigue crack propagation model was established combined with ABAQUS and FRANC3D. The numerical model was validated by experimental observations in the present study and open literature. A parametric analysis method considering initial pit depth and stress amplitude was proposed to evaluate the residual life of steel wires. The results showed that the linear elastic fracture mechanics and numerical simulation-based method can be used to assess the fatigue life of virgin and corroded steel wires.

Effect of Er on Microstructure and Corrosion Behavior of Al-Zn-Mg-Cu-Sc-Zr Aluminum Alloys.

In this study, the influence of Er addition on the microstructure, type transformation of second phases, and corrosion resistance of an Al–Zn–Mg–Cu alloy were explored. The results revealed that the added Er element could significantly refine the alloy grains and change the second-phase composition at the grain boundary of the alloy. In the as-cast state, the Er element significantly enhanced the corrosion resistance of the alloy due to its refining effect on the grains and second phases at the grain boundary. The addition of the alloying element Er to the investigated alloy changed the type of corrosion attack on the alloy’s surface. In the presence of Er, the dominant type of corrosion attack is pitting corrosion, while the alloy without Er is prone to intergranular corrosion attack. After a solution treatment, the Al8Cu4Er phase was formed, in which the interaction with the Cu element and the competitive growth relation to the Al3Er phase were the key factors influencing the corrosion resistance of the alloy. The anodic corrosion mechanism of the Al8Cu4Er and Al3Er phases evidently lowered the alloy corrosion rate, and the depth of the corrosion pit declined from 197 μm to 155 μm; however, further improvement of corrosion resistance was restricted by the morphology and size of the Al8Cu4Er phase after its formation and growth; therefore, adjusting the matching design of the Cu and Er elements can allow Er to improve the corrosion resistance of the Al–Zn–Mg–Cu aluminum alloy to the greatest extent.

The effect of salt composition on the stress-free and corrosion-fatigue performance of a fine-grained nickel-based superalloy

This paper describes work to study hot corrosion damage in the nickel-based gas turbine alloy RR1000 coated with various salts at 600 °C. Interest in type-II hot corrosion on the fatigue resistance of gas turbine alloys has increased to minimise power/thermal inefficiencies. Stress-free corrosion demonstrated a greater impact of sulphate (versus chloride) on maximum pit depth, a key influencing factor of fatigue lives. In corrosion-fatigue testing, at low stresses sulphate was shown to be more influential of fatigue life. At high stresses, the presence of greater crack initiation sites, reduced initiation lives and cracked oxide suggests chlorine influenced the crack-initiation behaviour.

The Validity of Iscan’s Age Estimation Method applied to the Fourth Rib in a Thai Male population

Abstract Iscan’s staging method for age estimation from fourth ribs has been proved to be a potentially useful tool for various populations. However, due to interracial variations, it is necessary to calibrate its’ accuracy in reference to a population of Thai males before it can be applied. This study aimed to evaluate the validity of phasing analyses of sternal ends of fourth ribs developed by Iscan, et al., on a Thai male population. The Iscan’s method was applied to 50 Thai males aged 18 years and above. Staging of sternal ends of the ribs was analyzed based on 3 morphological features: pit depth, pit shape, and rim and wall configurations – designated as components 1, 2, and 3, respectively. The data was analyzed using descriptive statistics, one-way ANOVA, and cross-tabulation with Kendall’s Tau-c correlation. It was found that sternal end stages of fourth ribs in each component, inclusive of composite scores, are positively correlated to the age of the individual (P < 0.001). However, Iscan’s result - which was derived from a population of white males - delivers age-underestimation in a Thai population. Hence, we developed a modified age prediction reference table for application to Thai males. Applying cross-tabulation analysis, stages 1 and 2 were found only in individuals who were less than 40 years old, and stages 4 and 5 were found only in the 40 years and above age-group except for 1 case. Keywords: Age estimation, Fourth rib, Iscan’s method, Thai male

A procedure for numerically model surface of the corroded specimen

ABSTRACT The paper presents a procedure for numerically modelling the surface of corroded specimens. A 3D laser scan is utilised to derive surface morphology and corrosion pit depth distribution. This corrosion depth is analyzed with a probability model to assess the morphology difference and the characteristic of the corrosion pit depth at a particular volumetric change. Furthermore, the goodness fit test statistic is carried out to observe the propensity of corrosion depth to a specific distribution, i.e. the Gaussian and non-Gaussian. The corroded specimens that conform to Gaussian distribution are numerically modelled with ANSYS APDL to generate a Gaussian surface. Furthermore, the non-Gaussian surface model is simplified as a single corrosion pit with various geometrical shapes. The mesh convergence is carried out to provide accurate stress distribution . The procedure is adjustable and applicable to the other surface morphology.

Mechanism of molten KOH+NaOH etching of GaN revealed by the slopes of etch pits formed at threading dislocations

The etch pit method is used widely to reveal dislocations in GaN via a molten KOH+NaOH solution. To understand the pit formation mechanism better, we performed a statistical analysis of the three-dimensional pit geometry. Particular attention was focused on the slope of the pit facet that forms an angle θ with the {0001} plane. It was found that tanθ is linearly proportional to the apparent pit depth D for a given type of dislocation. Therefore, the slope of the linear fitting (SLF) of tanθ vs. D/t (t is the etch time) could be used to identify the dislocation type and was more reliable than using pit widths. Transmission electron microscopy was used to confirm the results. It is thought that the SLF reflects the configuration of atomic steps at the dislocation core. Our results imply that pit formation is governed by thermodynamic pit nucleation at the dislocation core, followed by kinematic facet development.

Comparative life cycle cost assessment of (lean) duplex stainless steel in wastewater treatment environments

Some unit operations in wastewater treatment plants (WWTPs), such as settling tanks and pipes for aeration or sludge transfer, are composed of austenitic stainless steel (EN 1.4307 or EN 1.4404) instead of galvanised or painted carbon steel to reduce the maintenance costs. The sensitivity to pitting and crevice corrosion of austenitic grades in certain WWTP environments has also led to the use of duplex grades. The purpose of this study is to evaluate the maintenance of piping systems (WWTPs) and its effect on their life cycle environmental impacts and costs (LCC) for both austenitic and duplex stainless steel grades. The final objective is to aid grade selection for piping in a WWTP environment. The considered functional unit (FU) is a complete piping system. Conventional austenitic stainless steel grades (e.g., EN 1.4404) are studied alongside duplex ones (e.g., EN 1.4362 and EN 1.4462). The calculated environmental impacts are the Global Warming Potential (GWP) and Primary Energy Demand (PED). The production, manufacturing, transport, use including maintenance activities, and end-of-life (burdens and credits) phases are included in the life cycle assessment (LCA). The maintenance activities consist of the required replacements of stainless steel piping during the lifespan of the WWTP. Thus, the service lives of the pipes included in the considered WWTP environment are determined based on long-term corrosion prediction models (power law), which predict the evolution of pit or crevice depth as a function of time. The model parameters are estimated based on own experimental results, supplemented by the existing literature. The corrosion rates determine the number and frequency of replacements, i.e., define the different scenarios of maintenance. The LCA, LCC and corrosion prediction models are then combined into a user-friendly tool, which can be used in industry for an appropriate grade selection for pipes in a WWTP environment. The tool includes several degrees of freedom such as piping distribution, water pressure, chloride content, replacement criteria, etc. The results show that using duplex stainless steel grade EN 1.4462 leads to lower GWP and PED at the end of the WWTP's service life of 40 years. This is mainly due to multiple replacements of the system's parts in wastewater with high levels of chloride (>3000 ppm) if more conventional austenitic stainless steel alloys such as EN 1.4404 are used. Leaner duplex stainless steel grades were also included in this LCC assessment. The duplex grade EN 1.4062 showed the lowest total LCC, thanks to its leaner chemical composition (i.e., lower nickel content) combined with good localized corrosion resistance.

Mathematical modelling of microbial corrosion in carbon steel due to early-biofilm formation of sulfate-reducing bacteria via extracellular electron transfer

Sulfate-reducing bacteria (SRB) are the most studied microorganisms related to severe episodes of microbially influenced corrosion (MIC). A mechanism used by SRB to corrode steel alloys is the extracellular electron transfer (EET), which was described by the biocatalytic cathodic sulfate reduction (BCSR) theory. This theory was supported by several experimental research and some mathematical approaches. However, mathematical modelling that represents the effect of the EET on pit development and the subsequent changes in surface topography has not been reported. In this study, a mechanistic mathematical model of microbial corrosion induced by SRB through EET was developed and implemented. The developed model used data from previously reported experiments to describe the phenomenon and define stoichiometric and kinetic parameters. Results of biofilm development and growth-associated corrosion (i.e. weight loss and maximum pit depths) obtained by simulations were similar to experimental evidence reported in the literature. These simulations reveal that the main parameters that control MIC are the maintenance coefficient of SRB, the initial planktonic cell concentration, and the probability of surface colonization.

Micro-cutting force model of micro-jet induced by cavitation collapse in the ultrasonic field at micro-nano scale

The micro-jet is the main mechanism of cavitation on materials. More and more ultrasonic cavitation assisted machining uses the micro-jet effect in the industrial field. In this paper, the micro-jet impact is considered the micro-cutting process. To deeply analyze the micro-cutting mechanism of micro-jet, the size effect of materials was considered, and the micro-cutting force model of micro-jet was established and solved based on the spherical indentation test theory and the strain gradient plasticity theory. The results showed that the micro-cutting force and impact pressure of micro-jet with size effect are larger than those without size effect and the micro-cutting force of single micro-jet is within 2.35 N. The micro-cutting force of micro-jet increases exponentially with the increase of pit radius, but only slightly increases with the increase of pit depth. When the size effect is considered or not, the impact pressure of micro-jet is 1616–2922 MPa or 1615–1980 MPa, respectively. The increased ratio of micro-cutting force with size effect is \(\left(\sqrt{1+\frac{2{\overline{m} }^{2}{a}^{2}{G}^{2}bh}{\left({a}^{2}+{h}^{2}\right){\sigma }_{\mathrm{JC}}^{2}}-1}\right)\times 100\%\), which can directly reflect the strength of size effect. The size effect is more obvious when the pit size is smaller, and the maximum increased ratio is 47.54%. The increased ratio increases nonlinearly with the decrease of pit radius and the increase of pit depth. It has a strong correlation with pit radius and pit depth. This paper can provide a theoretical viewpoint and support for the quantitative description of cavitation effect in ultrasonic-assisted machining.

Food-grade D-limonene enhanced a green biocide in the mitigation of carbon steel biocorrosion by a mixed-culture biofilm consortium.

Microbiologically influenced corrosion (MIC), or microbial biocorrosion, is caused directly by microbial metabolic activities/products or induced by microbial biofilm's damage of a protective film that exposes a solid surface to a pre-existing corrosive environment. MIC causes billions of dollars of losses in various industrial processes, especially in oil and gas and water utilities. The mitigation of problematic industrial microbes typically relies on biocides whose discharges can cause environmental problems. Thus, more effective biocide applications are desired to minimize environmental impact. D-Limonene, a citrus peel oil, generally regarded as safe (GRAS), was used to enhance the popular biodegradable tetrakis hydroxymethyl phosphonium sulfate (THPS) biocide. An oilfield mixed-culture biofilm was grown anaerobically in enriched artificial seawater containing C1018 carbon steel coupons for 7days at 37°C. One hundred ppm (w/w) D-limonene reduced general heterotrophic bacteria (GHB) and acid-producing bacteria (APB) effectively, leading to 5.4-log and 6.0-log reductions in sessile GHB and APB cell counts, respectively, compared to no treatment control. The combination of 100ppm D-limonene + 100ppm THPS achieved extra 1.0-log SRB, 0.6-log GHB and 0.5-log APB reductions in sessile cell counts, which led to extra 58% reduction in microbial corrosion mass loss (1.2 vs. 0.5mg/cm2) and extra 30% reductions in maximum pit depth (11.5 vs. 8.1µm), compared to 100ppm THPS-only treatment. Linear polarization resistance and potentiodynamic polarization (PDP) corrosion data supported mass loss and pitting data. Mixed-culture biofilms on carbon steel coupons after 7day incubation at 37°C showing enhanced biocide treatment outcome using D-limonene + THPS: A no treatment, B 100ppm D-limonene, C 100ppm THPS, D 100ppm D-limonene + 100ppm THPS.

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.

Evaluation of trehalase as an enhancer for a green biocide in the mitigation of Desulfovibrio vulgaris biocorrosion of carbon steel.

Trehalase can biocatalyze the conversion of trehalose to glucose. It is an enzyme that plays an important role in biofilm formation. Thus, trehalase has been patented as a chemical for preventing and treating biofilms. Sulfate-reducing bacteria (SRB) biofilms are often found responsible for biocorrosion, also known as microbiologically infuenced corrosion (MIC), especially in the oil and gas industries and in water utilities. The MIC treatment process typically requires biocide treatment of biofilms, sometimes together with scrubbing. Owing to environmental concerns, a lower biocide dosage is desired in the treatment process. In this work, trehalase was tested as a green biocide enhancer to enhance tetrakis hydroxymethyl phosphonium sulfate (THPS) in the prevention of Desulfovibrio vulgaris MIC of C1018 carbon steel in ATCC 1249 culture medium at 37°C. THPS is one of the most popular industrial biocides owing to its broad-spectrum efficacy and green chemical status. After 7days of incubation in 50mL anaerobic vials containing 40mL culture medium at pH 7.0, the sessile cell counts indicated that 50ppm (w/w) THPS + 30ppm (w/w) trehalase led to an extra 5.7-fold sessile cell reduction when compared with the 50ppm THPS alone treatment. As a consequence, the combination treatment also resulted in an extra 54% in pit depth reduction and 30% in weight loss reduction when compared with the 50ppm THPS alone treatment (with 9.0μm and 1.0mg/cm2). The biofilm images corroborated the decreased sessile cell count and pitting corrosion.