Investigation into Effects of Coating on Stress Corrosion of Cable Bolts in Deep Underground Environments.

Due to the intricate and volatile nature of the service environment surrounding prestressing anchoring materials, stress corrosion poses a significant challenge to the sustained stability of underground reinforcement systems. Consequently, it is imperative to identify effective countermeasures against stress corrosion failure in cable bolts within deep underground environments, thereby ensuring the safety of deep resource extraction processes. In this study, the influence of various coatings on the stress corrosion resistance of cable bolts was meticulously examined and evaluated using specifically designed stress-corrosion-testing systems. The specimens were subjected to loading using four-point bending frames and exposed to simulated underground corrosive environments. A detailed analysis and comparison of the failure patterns and mechanisms of specimens coated with different materials were conducted through the meticulous observation of fractographic features. The results revealed stark differences in the stress corrosion behavior of coated and uncoated bolts. Notably, epoxy coatings and chlorinated rubber coatings exhibited superior anti-corrosion capabilities. Conversely, galvanized layers demonstrated the weakest effect due to their sacrificial anti-corrosion mechanism. Furthermore, the effectiveness of the coatings was found to be closely linked to the curing agent and additives used. The findings provide valuable insights for the design and selection of coatings that can enhance the durability and reliability of cable bolts in deep underground environments.

The influence Cl- on stress corrosion of 7xxx series aluminium alloys studied by experimental and simulation technology.

The stress corrosion behavior of 7xxx series aluminium alloys in different concentrations NaCl solution was studied, and numerical simulation was conducted in COMSOL Multiphysics based on experimental results. Different stresses were applied on the experiment pieces, the pitting crater deepened with the change of stress level. The corrosion rate increased with the raising stress. There is no positive correlation between stress corrosion degree and chloride ion concentration. The most severe corrosion occurs in 5.0 wt% NaCl solution instead of 6.0 wt% NaCl solution due to the increase of water film conductivity and decrease of solubility of oxygen under high Cl- environment. The finite element model was used to analyze the stress distribution on aluminium alloy surface, to describe the dynamic equation of anodic dissolution of metal due to elastic and plastic deformation. Corrosion occurs mainly in stress concentrated areas. When the stress loading exceeds a certain threshold, plastic strain occurs on the surface of both the specimen and the structural part, the corrosion current density increases instantaneously, and the corrosion behavior in the stress concentration area gradually intensifies. The survey can provide practical theoretical guidance for predicting stress corrosion and extending the service life of equipment in (harsh) marine environments.

Symmetrical structure design of PLGA Biodegradable sinus stents and structure optimization based on surrogate models.

This study aims to enhance the degradation uniformity of PLGA sinus stents to minimize fracture risk caused by stress corrosion. Symmetric stent structures were introduced and compared to sinusoidal structure in terms of stress and degradation uniformity during implantation and degradation processes. Three surrogate models were employed to optimize the honeycomb-like structure. Results showed honeycomb-like structures exhibited the superior stress distribution and highest degradation uniformity. The kriging model achieved the smallest error and degradation uniformity of 83.24%. In conclusion, enhancing the symmetry of stent structures improves degradation uniformity, and the kriging model has potential for the optimization of stent structures.

Data analysis of the influence of microstructure, composition, and loading conditions on stress corrosion cracking behavior of Mg alloys.

Stress corrosion cracking (SCC) can be a crucial problem in applying rare earth (RE) Magnesium alloys in environments where mechanical loads and electrochemical driven degradation processes interact. It has been proven already that the SCC behavior is associated with microstructural features, compositions, loading conditions, and corrosive media, especially in-vivo. However, it is still unclear when and how mechanisms acting on multiple scales and respective system descriptors predictable contribute to SCC for the wide set of existing Mg alloys. In the present work, suitable literature data along SCC of Mg alloys has been analyzed to enable the development of a reliable SCC model for MgGd binary alloys. Pearson correlation coefficient and linear fitting are utilized to describe the contribution of selected parameters to corrosion and mechanical properties. Based on our data analysis, a parameter ranking is obtained, providing information on the SCC impact with regard to ultimate tensile strength (UTS) and fracture elongation of respective materials. According to the analyzed data, SCC susceptibility can be grouped and mapped onto Ashby type diagrams for UTS and elongation of respective base materials tested in air and in corrosive media. The analysis reveals the effect of secondary phase content as a crucial materials descriptor for our analyzed materials and enables better understanding towards SCC model development for Mg-5Gd alloy based implant.

Investigation of Multi-Factor Stress Corrosion Cracking Failure of Safe-End Feedwater Lines of Submarine Power System.

The corrosion process under the complex safe-end feedwater line conditions was investigated via experimental lab testing and numerical simulation. The corrosion of safe-end feedwater lines was controlled through the combination of galvanic corrosion, residual stress, and flow velocity. Firstly, galvanic corrosion occurred once the 20 steel was welded with 316L stainless steel. The pitting corrosion could be observed on the 20 steel side of the weld joint. Secondly, a vortex flow was detected around the welding bump and within the pits. The growth of the pits was accelerated in both the vertical and horizontal directions. Finally, under the residual stress condition, the stress intensity factor (K) at the bottom of the pits was easier to reach than the critical stress intensity factor (KISCC). Then, pitting was transformed into stress corrosion cracking which then propagated along the weld line. Therefore, the critical factor inducing the failure of safe-end feedwater lines was the combined action of galvanic corrosion, residual stress, and flow velocity.

Stress corrosion cracking under extreme near-neutral GCC conditions, parametric and comparative study using phase field modeling.

Stress Corrosion Cracking (SCC) is a failure mechanism that occurs when certain materials are subjected to both external or residual stresses and corrosion. This combined effect leads to the development of cracks in the susceptible materials. Submerged steel pipelines in the petroleum sector are built of low-alloy steels having a ferrite-cementite composition, including API 5L X70. Such materials are sensitive to SCC damage in aqueous systems. The film rupture dissolution repassivation (FRDR) process is used in this study to evaluate the cracks and pits growth in oil and gas pipelines in the Gulf area under diverse SCC environmental conditions. The SCC crack propagation and pit growth under near-neutral environmental conditions were analyzed using phase field modelling. X70 steel under NS4 the solution was used for the analysis to represent the anodic dissolution film rupture mechanism. A parametric study was done to study the impact of different electrochemistry and phase field parameters on crack growth behaviour. The study assess the susceptibility to SCC caused by an pit by employing diverse settings to evaluate the impact of corrosion parameters and the interaction among the FRDR mechanism. The corrosion rates are influenced by the interface kinetics coefficient (L), which exhibits an accelerated effect as L increases. This transition from fracture-controlled to dissolution-controlled SCC growth occurs until the system reaches the diffusion limit, beyond which further increases in L do not significantly impact corrosion rates. Moreover, higher values of the kinetic coefficient (k) advance the creation of SCC cracks at the crack front, resulting from corrosion originating from pitting at the crack mouth. This process leads to the refinement of the pit and its transformation into a crack. A comparison analysis was utilized to validate our simulation under a near-neutral NS4 solution for X70 steel by correlating the findings with other numerical methods for crack growth utilizing the same material and environmental parameters. The results show decent agreement with the comparative study.

Human Body-Fluid-Assisted Fracture of Zinc Alloys as Biodegradable Temporary Implants: Challenges, Research Needs and Way Forward.

Alloys of magnesium, zinc or iron that do not contain toxic elements are attractive as construction material for biodegradable implants, i.e., the type of implants that harmlessly dissolve away within the human body after they have completed their intended task. The synergistic influence of mechanical stress and corrosive human body fluid can cause sudden and catastrophic fracture of bioimplants due to phenomena such as stress corrosion cracking (SCC) and corrosion fatigue (CF). To date, SCC and CF of implants based on Zn have scarcely been investigated. This article is an overview of the challenges, research needs and way forward in understanding human body-fluid-assisted fractures (i.e., SCC and CF) of Zn alloys in human body fluid.

Stress Corrosion Cracking of 316L Stainless Steel Additively Manufactured with Sinter-Based Material Extrusion.

This study investigates the stress corrosion cracking (SCC) behavior of type 316L stainless steel (SS316L) produced with sinter-based material extrusion additive manufacturing (AM). Sinter-based material extrusion AM produces SS316L with microstructures and mechanical properties comparable to its wrought counterpart in the annealed condition. However, despite extensive research on SCC of SS316L, little is known about the SCC of sinter-based AM SS316L. This study focuses on the influence of sintered microstructures on SCC initiation and crack-branching susceptibility. Custom-made C-rings were exposed to different stress levels in acidic chloride solutions at various temperatures. Solution-annealed (SA) and cold-drawn (CD) wrought SS316L were also tested to understand the SCC behavior of SS316L better. Results showed that sinter-based AM SS316L was more susceptible to SCC initiation than SA wrought SS316L but more resistant than CD wrought SS316L, as determined by the crack initiation time. Sinter-based AM SS316L showed a noticeably lower tendency for crack-branching than both wrought SS316L counterparts. The investigation was supported by comprehensive pre- and post-test microanalysis using light optical microscopy, scanning electron microscopy, electron backscatter diffraction, and micro-computed tomography.

Investigation of Stress Corrosion Cracking Resistance of Irradiated 12Cr Ferritic-Martensitic Stainless Steel in Supercritical Water Environment.

The supercritical water-cooled reactors (SWCR) belong to Generation IV of reactors. These reactors have a number of advantages over currently operating WWERs and PWRs. These advantages include higher thermal efficiency, a more simplified unit design, and the possibility of incorporating it into a closed fuel cycle. It is therefore necessary to identify candidate materials for the SWCR and validate the safety and effectiveness of their use. 12Cr ferritic-martensitic (F/M) stainless steel is considered a candidate material for SWCR internals. Radiation embrittlement and corrosion cracking in the primary circuit coolant environment are the main mechanisms of F/M steels degradation during SWCR operation. Here, the stress corrosion cracking (SCC) in supercritical water at 390 and 550 °C of 12Cr F/M steel irradiated by neutrons to 12 dpa is investigated. Autoclave tests of specially designed disk specimens in supercritical water were performed. The tests were carried out under different constant load (CL), temperature 450 °C, and pressure in autoclave 25 MPa. The threshold stress, below which the SCC initiation of irradiated 12Cr F/M steel does not occur, was determined.

Attaining High Functional Performance in Biodegradable Mg-Alloys: An Overview of Challenges and Prospects for the Mg-Zn-Ca System.

This article presents a concise overview of modern achievements and existing knowledge gaps in the area of biodegradable magnesium alloys. Hundreds of Mg-based alloys have been proposed as candidates for temporary implants, and this number tends to increase day by day. Therefore, while reviewing common aspects of research in this field, we confine ourselves primarily to the popular Mg-Zn-Ca system, taken as a representative example. Over the last decades, research activities in this area have grown enormously and have produced many exciting results. Aiming at highlighting the areas where research efforts are still scarce, we review the state-of-the-art processing techniques and summarize the functional properties attained via a wide variety of processing routes devised towards achieving a desired properties profile, including the mechanical response in terms of strength, ductility, and fatigue resistance paired with biocompatibility and bio-corrosion resistance or controlled degradability. We pay keen attention to a summary of corrosion properties and mechano-chemical interactions between an aggressive environment and loaded Mg-based structures, resulting in stress corrosion cracking and premature corrosion fatigue failures. The polemic issues and challenges practitioners face in their laboratory research are identified and discussed.

Effect of the Combination of Torsional and Tensile Stress on Corrosion Behaviors of Biodegradable WE43 Alloy in Simulated Body Fluid.

The real physiological environment of the human body is complicated, with different degrees and forms of loads applied to biomedical implants caused by the daily life of the patients, which will definitely influence the degradation behaviors of Mg-based biodegradable implants. In the present study, the degradation behaviors of modified WE43 alloys under the combination of torsional and tensile stress were systematically investigated. Slow strain rate tensile tests revealed that the simulated body fluid (SBF) solution could deteriorate the ultimate tensile stress of WE43 alloy from 210.1 MPa to 169.2 MPa. In the meantime, the fracture surface of the specimens tested in the SBF showed an intergranular corrosion morphology in the marginal region, while the central area appeared not to have been affected by the corrosive media. The bio-degradation performances under the combination of torsional and tensile stressed conditions were much more severe than those under unstressed conditions or single tensile stressed situations. The combination of 40 MPa tensile and 40 MPa torsional stress resulted in a degradation rate over 20 mm/y, which was much higher than those under 80 MPa single tensile stress (4.5 mm/y) or 80 MPa single torsional stress (13.1 mm/y). The dynamic formation and destruction mechanism of the protective corrosion products film on the modified WE43 alloy could attribute to the exacerbated degradation performance and the unique corrosion morphology. The dynamic environment and multi-directional loading could severely accelerate the degradation process of modified WE43 alloy. Therefore, the SCC susceptibility derived from a single directional test may be not suitable for practical purposes. Complex external stress was necessary to simulate the in vivo environment for the development of biodegradable Mg-based implants for clinical applications.

Failure analysis of local settlement induced Q345R bottom plate cracking of crude oil storage tank.

A 5000m3 single deck floating roof crude oil storage tank was found to have a cracked Q345R bottom plate during an open tank inspection. To analyze the cause of the failure, a series of experiments were carried out. The results showed that the chemical composition of the failed crude oil storage tank bottom plate material Q345R had a slight excess of S, V, and Ti which causes the material to form a bainite structure, resulting in a hard and brittle material with poor toughness. Q345R is susceptive to H2S stress corrosion cracking according to SCC test. Based on the working condition investigation, the cracked plate was subjected to the local settlement and H2S contained corrosive medium. With the stress concentration induced by local settlement, the bottom plate cracked. In order to avoid such incidents, Q345R material should be avoided in H2S containing environment, and online monitoring should be carried out regularly to assess the overall condition of the tanks.

The Failure Mechanism of the 316 SS Heat Exchanger Tube in the Geothermal Water Environment.

In this work, the intrinsic reason for the premature failure of a 316 stainless steel heat exchanger tube in geothermal water environment is disclosed. The chemical composition of the tube was tested, and the microstructure was examined for material inspection. Fracture morphology and secondary cracks were analyzed, and electron backscattered diffraction was applied to explore the crack propagation mode. The corrosion morphology was observed. The electrochemical behavior was studied with cyclic polarization and double-loop electrochemical potentiokinetic reactivation. It is found that the main failure cause was stress corrosion cracking (SCC). Attacked by chloride ions, the tube is susceptible to SCC under the residual stress as a result of the substandard Mo and Ni content. The SCC mechanism is localized anodic dissolution, and the propagation mode is a mixture of transgranular SCC and intergranular SCC.

Effect of Air Storage on Stress Corrosion Cracking of ZK60 Alloy Induced by Preliminary Immersion in NaCl-Based Corrosion Solution.

The preliminary exposure of Mg alloys to corrosion solutions can cause their embrittlement. The phenomenon is referred to as pre-exposure stress corrosion cracking (PESCC). It has been reported that relatively long storage in air after pre-exposure to the corrosion solution is capable of eliminating PESCC. This effect was attributed to the egress of diffusible hydrogen that accumulated in the metal during pre-exposure. However, recent findings challenged this viewpoint and suggested that the corrosion solution retained within the side surface layer of corrosion products could be responsible for PESCC. The present study is aimed at the clarification of the role of hydrogen and the corrosion solution sealed within the corrosion products in the "healing" effect caused by post-exposure storage in air. Using the slow strain rate tensile (SSRT) testing in air and detailed fractographic analysis of the ZK60 specimens subjected to the liquid corrosion followed by storage in air, we found that PESCC was gradually reduced and finally suppressed with the increasing time and temperature of air storage. The complete elimination of PESCC accompanied by recovery of elongation to failure from 20% to 38% was achieved after 24 h of air storage at 150-200 °C. It is established that the characteristic PESCC zone on the fracture surface is composed of two regions, of which the first is always covered by the crust of corrosion products, whereas the second one is free of corrosion products and is characterised by quasi-brittle morphology. It is argued that the corrosion solution and hydrogen stored within the corrosion product layer are responsible for the formation of these two zones, respectively.

Correlation of Lack of Fusion Pores with Stress Corrosion Cracking Susceptibility of L-PBF 316L: Effect of Surface Residual Stresses.

Stress corrosion cracking (SCC) of laser powder bed fusion-fabricated 316L was studied under the variation in energy input density to emulate the existence of distinctive types of defects. Various electrochemical polarization measurements were performed in as-received polished and ground states, to elucidate the effect of defect type on corrosion and SCC behaviour in marine solution. The results revealed severe localized corrosion attack and SCC initiation for specimens with a lack of fusion pores (LOF). Moreover, the morphology of SCC was different, highlighting a more dominant effect of selective dissolution of the subgrain matrix for gas porosities and a more pronounced effect of brittle fracture at laser track boundaries for the specimens with LOF pores.

Effects of Multi-Pass Turning on Stress Corrosion Cracking of AISI 304 Austenitic Stainless Steel.

Austenitic stainless steels are extensively used in mechanical engineering. The machined surface integrity has an essential influence on the stress corrosion cracking (SCC) performance of stainless steels. In this paper, the effects of multi-pass turning on the SCC susceptibility of AISI 304 austenitic stainless steel were investigated by correlating the SCC crack density to the machining-induced surface characteristics in terms of roughness, micro-hardness, and residual stress. In the multi-pass turning, the surface roughness and residual stress were the least after the double pass turning, and the surface micro-hardness was the maximum after the triple-pass turning. The SCC susceptibility was evaluated after SCC tests in boiling MgCl2 solution. The results showed that the weakest SCC sensitivity was observed in double-pass turning 304 stainless steel, while the most susceptible SCC was found in triple-pass turning. Compared with the double-pass turning, the increase in SCC sensitivity of triple-pass turning was attributed to the larger roughness, higher micro-hardness and greater residual tensile stresses.

Microstructural Effects in the Development of Near-Neutral pH Stress Corrosion Cracks in Pipelines.

The corrosion and stress corrosion cracking (SCC) behaviors of 20#, X60, and X80 pipeline steels in a near-neutral pH environment were investigated by means of electrochemical measurement, immersion test, and interrupted slow strain rate tensile (SSRT) test. The propensity for SCC, as indicated by the stress threshold value for crack initiation, was found to be dependent on the type of steel microstructure. Cracks were initiated in the high-strength steel X80 at a stress less than its yield strength, whereas in the other lower-grade steels, the initiation of cracks occurred after the yielding point. The threshold stress of SCC initiation in the near-neutral pH environment for 20#, X60, and X80 steels were 130.64% σys, 106.79% σys, and 86.92% σys, respectively. The SCC of 20# and X60 were characterized by the formation of transgranular and intergranular cracks, while X80 steel was only by transgranular cracking. The occurrence of corrosion had a great effect on crack initiation and the growth at the later stage. The latter involved hydrogen effects. A correlation between SCC sensitivity and the yield strength of the steel has been identified.

Electrochemical Evaluation of Stress Corrosion Cracking Susceptibility of Ti-6Al-3Nb-2Zr-1Mo Alloy Welded Joint in Simulated Deep-Sea Environment.

Titanium alloys have high specific strength and excellent corrosion resistance and have been applied in deep-sea engineering fields. However, stress corrosion cracking may become one of the biggest threats to the service safety of a high-strength titanium alloy, as well as its weldment. In this work, stress corrosion cracking of a gas-tungsten-arc-welded Ti-6Al-3Nb-2Zr-1Mo (Ti6321) alloy influenced by the applied potentials in simulated deep-sea and shallow-sea environments was investigated by combining slow strain rate testing with electrochemical measurements. The results showed that the service environment and applied potential have a substantial effect on the stress corrosion cracking behavior of the Ti6321 welded joint. The Ti6321 welded joint exhibited higher stress corrosion susceptibility in a simulated deep-sea environment and at a strong polarization level owing to the diminishing protection of the passive film under passivation inhibition and the enhancement of the hydrogen effect. The fracture of a Ti6321 welded joint in the weld material could be attributed to the softening effect of the thick secondary α within the coarse-grained martensite. The electrochemical evaluation model of stress corrosion cracking susceptibility of a Ti6321 welded joint in a simulated marine environment was established by adding the criterion in the passivation region based on the literature model, and four potential regions corresponding to different stress corrosion cracking mechanisms were classified and discussed. Our study provides useful guidance for the deep-sea engineering applications of Ti6321 alloys and a rapid assessment method of stress corrosion risk.

Role of non-carious cervical lesions multicausality in the behavior of respective restorations.

OBJECTIVES: To evaluate biocorrosion and eccentric occlusal loading interplay in marginal quality of cervical restorations. METHODS: Cervical wedge-shaped cavities were prepared in extracted premolars and restored with a composite. Premolars underwent either an erosive challenge (E: 1% citric acid/10 min), eccentric occlusal loading (EOL: 150 N/2.5 Hz/106 cycles), E before EOL (E + EOL), E intermediate to EOL (EOL/E/EOL), E after EOL (EOL + E), or no E or EOL (C: control). Marginal quality was analyzed based on a series of Optical Coherence Tomography images. Each of the margins was assigned a gap score (0, 1, 2, or 3) and measurement (µm). For each margin, scores data were analyzed with Kruskall Wallis and Dunn tests, and µm data, with Kruskall Wallis. Overall and for each group, the different margins were compared using Wilcoxon signed-rank test, and the correlation between scores and µm, Spearman's correlation coefficient (α = 0.05). RESULTS: E and EOL, even if associated, did not influence enamel marginal quality. EOL/E/EOL impaired dentin/cementum marginal quality only in the case of scores and compared to E. E + EOL, EOL + E or EOL and even C, without differences between each other, did not influence results differently from E or EOL/E/EOL. Margins in dentin/cementum always showed lengthier gaps. Except for C, E and EOL + E cervical margin, there was a strong positive correlation between scores and µm. CONCLUSIONS: Eccentric occlusal loading and/or biocorrosion cannot be assumed as causes of marginal failure of cervical restorations in wedge-shaped cavities. A relevant concern may still be the establishment of adhesive interfaces in dentin/cementum. CLINICAL SIGNIFICANCE: Although non-carious cervical lesions are strongly being recognized multifactorial and their respective restorations not always behave as expected, biocorrosion and eccentric occlusal loading interplay cannot serve as an explanation for marginal gaps they often present.

Effects of Temperature and Applied Potential on the Stress Corrosion Cracking of X80 Steel in a Xinzhou Simulated Soil Solution.

In this research, the stress corrosion cracking (SCC) behavior of X80 pipeline steel in a Xinzhou soil environment at different temperatures and applied potentials was studied with a slow strain rate test (SSRT), potentiodynamic polarization curve measurements, and scanning electron microscopy (SEM). When a higher anodic potential was applied, anodic dissolution occurred at the crack tip and on the crack wall. The cracking mechanism of X80 steel in Xinzhou soil solution is anodic dissolution (AD). At positive cathodic potentials, X80 steel is under an anodic polarization state at the crack tip and under a cathodic polarization state at the crack wall. The SCC of X80 steel is affected by the combined effects of anodic dissolution (AD) and hydrogen embrittlement (HE). At more negative cathodic potentials, both crack tips and crack walls are under cathodic polarization. The SCC of X80 steel is dominated by hydrogen embrittlement (HE). SCC susceptibility has the same variation trend with potentials at different temperatures. The susceptibility to SCC increases notably as the temperature increases at weak cathodic potentials and open circuit potential due to the effect of temperature on the corrosion potential and the diffusion of atoms.