Stress Corrosion Crack Propagation Research Articles

A comparative study on the passive film and SCC behavior of Ti-6Al-3Nb-2Zr-1Mo alloy at various test temperatures in simulated seawater

In this work, the electrochemical and stress corrosion cracking (SCC) behavior of Ti-6Al-3Nb-2Zr-1Mo alloy in simulated seawater at various solution temperatures were systematically studied. Results show rising test temperature increases the point defect density in passive film and deteriorates the stability. Therefore, SCC is promoted by localized anodic dissolution (AD). At 25 °C, SCC initiates in αp phase, and β phase hinders SCC propagation on account of the lower electrochemical activity induced by element segregation. While at 4 °C, the SCC propagation rate is higher than that at 25 °C, as the SCC propagation resistance of β phases decreases.

Effect of laser shock peening on stress corrosion cracking of TC4/2A14 dissimilar metal friction stir welding joints

Stress corrosion cracking (SCC) of welded joints is a significant issue that affects the widespread application of multimetal welded structures in aerospace, transportation, and other fields. This paper investigates the effect of laser shock peening (LSP) on the SCC of TC4/2A14 friction stir welded (FSW) joints with dissimilar metals. The microstructural evolution, mechanical properties, and corrosion behavior with and without LSP treatment were investigated using optical microscopy, transmission electron microscopy, X-ray analysis, electrochemical testing, and slow strain rate tensile testing (SSRT). The results showed that the LSP significantly refined the grains and induced work-hardening on the near-surface of the material. After LSP, the compressive residual stresses on the surface of the titanium and aluminium sides were −817.6 MPa and −153.6 MPa for the joint, respectively. Corrosion resistance was also improved, with the self-corrosion current density on the Al side of the joints reduced by 77% and the SCC susceptibility index (Issrt) reduced from 0.140 to 0.121. The enhanced SCC resistance of the LSP-treated TC4/2A14 dissimilar metal FSW joints is primarily due to grain refinement, work-hardening effect, and high-level compressive residual stress. These factors not only enhance the material strength and improve the pitting resistance of the joints but also prevent the initiation and propagation of SCC.

Stress corrosion crack propagation behaviour of MAO ceramic coating on Mg alloy

This study investigates the impact of static tensile loads on magnesium (Mg) alloys with and without ceramic coatings in simulated body fluids (SBF) using a combination of numerical simulation and experimental methods. The surface of an AZ31B Mg alloy was treated with a ceramic coating via micro-arc oxidation (MAO). Subsequently, bare Mg-alloy and MAO ceramic-coated specimens were subjected to static tensile stress testing using a tensiometer. After immersion for 12 h in SBF, the surface morphology and electrochemical corrosion of the stressed specimens were analysed. Notably, under the same tensile stress, the Mg alloy in the SBF exhibited more severe corrosion damage than the ceramic-coated specimen. Furthermore, there was a direct correlation between the corrosion rate of the ceramic coating and the magnitude of the applied tensile stress. Overall, the MAO ceramic coating exhibited superior corrosion resistance compared to the bare Mg alloy, even after undergoing static tensile stresses. The study demonstrates that MAO ceramic coatings can enhance the corrosion resistance of biodegradable Mg implants by protecting them from the combined effects of bodily stresses and fluids.

Assessing the release, transport, and retention of radioactive aerosols from hypothetical breaches in spent fuel storage canisters

Interim dry storage of spent nuclear fuel involves storing the fuel in welded stainless-steel canisters. Under certain conditions, the canisters could be subjected to environments that may promote stress corrosion cracking leading to a risk of breach and release of aerosol-sized particulate from the interior of the canister to the external environment through the crack. Research is currently under way by several laboratories to better understand the formation and propagation of stress corrosion cracks, however little work has been done to quantitatively assess the potential aerosol release. The purpose of the present work is to introduce a reliable generic numerical model for prediction of aerosol transport, deposition, and plugging in leak paths similar to stress corrosion cracks, while accounting for potential plugging from particle deposition. The model is dynamic (changing leak path geometry due to plugging) and it relies on the numerical solution of the aerosol transport equation in one dimension using finite differences. The model’s capabilities were also incorporated into a Graphical User Interface (GUI) that was developed to enhance user accessibility. Model validation efforts presented in this paper compare the model’s predictions with recent experimental data from Sandia National Laboratories (SNL) and results available in literature. We expect this model to improve the accuracy of consequence assessments and reduce the uncertainty of radiological consequence estimations in the remote event of a through-wall breach in dry cask storage systems.

Pioneering research on the role of strain burst in the early-stage stress corrosion crack propagation

This work pioneered the study on the effect of cyclic-loading-induced strain burst on Stage-1b stress corrosion crack (SCC) growth under alternating static and cyclic loading. Results show that Stage-1b growth occurred by microcrack initiation and its linking to the main crack's tip. Increasing static hold duration caused crack growth rate per cycle to increase after an incubation period. This was because the occurrence of strain burst induced a high strain rate, leading to film rupture, and thus microcrack initiation. The effects of different stress levels and durations of static hold, and their interactions with cyclic loading, on crack growth were systematically studied.

Stress Corrosion Cracking of High-Strength Ni-Base Alloys in Pressurized Water Reactor Primary Water Containing KOH vs. LiOH

The stress corrosion cracking (SCC) behavior of high-strength Ni-base Alloys X-750 and 718 has been investigated to assess the effect of replacing LiOH with KOH as the pH moderator in pressurized water reactor (PWR) primary circuit coolant. The SCC initiation behavior of X-750 was evaluated by multitensile specimen constant load test in either LiOH- or KOH-containing PWR primary water. The SCC growth behavior of X-750 and Alloy 718 was evaluated on compact tension specimens with on-the-fly changes between LiOH- and KOH-containing water in three different PWR primary water chemistries. Direct current potential drop technique was used for in situ monitoring of crack initiation time and crack extension in SCC initiation and propagation tests, respectively. The results suggest no significant effect of KOH vs. LiOH on the SCC initiation or propagation of the tested materials.

Stress Measurement of Stainless Steel Piping Welds by Complementary Use of High-Energy Synchrotron X-rays and Neutrons

Probabilistic fracture mechanics (PFM) is increasingly recognized as a viable approach for evaluating the structural integrity of nuclear components, such as piping, primarily affected by stress corrosion cracking (SCC). PFM analysis requires several input parameters, among which welding residual stress is critically important due to its significant influence on SCC initiation and propagation. Recently, a novel technique involving a double-exposure method (DEM) utilizing synchrotron X-rays was introduced as an effective means for measuring welding residual stress with high spatial resolution. In this paper, we applied DEM to assess the residual stress of a plate specimen, which was extracted from a welded pipe through electrical discharge machining. Consequently, detailed stress maps under a plane stress state were generated. Additionally, the residual stress distributions in the welded pipe under a triaxial stress state were evaluated using neutron diffraction. Based on these findings, we proposed a methodology to acquire detailed stress maps of welded pipes by combining high-energy synchrotron X-rays and neutron diffraction.

Electrochemical potential dependence of SCC initiation in X60 pipeline steel in near-neutral pH environment

Stress corrosion crack (SCC) in pipelines directly affects the long-term safety service and has a major impact on the continuity of oil and gas delivery. The near-neutral pH SCC propagation process has been widely reported in the past decades, while the crack initiation mechanism is rarely studied in-depth. Here, the crack initiation behavior of ×60 pipeline steel under different electrochemical potential levels was investigated by interrupted slow strain rate tensile testing (SSRT) and microstructural characterization. The experimental results show that the SCC initiation is dominated by hydrogen-facilitated anodic dissolution (AD) under the open circuit potential (OCP) environment, while it is by the hydrogen embrittlement (HE) under −1.1 and −1.2 VSCE cathodic potentials. All the SCC cracks in ×60 pipeline steel show transgranular features, pathing through the grains in different crystallographic orientations, which showed dependence on the electrochemical potential of the steel: initiation via slip-enhanced dissolution of {110}//ND or {112}//ND texture under OCP environment, but mostly by quasi-cleavage cracking of {100}//ND texture under −1.1 and −1.2 VSCE cathodic potentials.

Insights into the stress corrosion cracking propagation behavior of Alloy 690 and 316 L stainless steel in KOH versus LiOH oxygenated water

The stress corrosion cracking (SCC) propagation behavior of 20% cold worked 316 L stainless steel (SS) and Alloy 690 was investigated in high-temperature oxygenated water. No discernable effect was observed at the same pH level for LiOH or KOH. Increasing pH could dramatically enhance the crack growth rates (CGRs) due to the dissolution of Cr-rich oxide film and the weakening of passivity in high pH regimes. The similarities in SCC behavior and cracking characteristics indicate that the cracking mechanism of both austenite alloys occurs by a slip-dissolution model.

Effect of Thermo-Mechanical Processing on Initiation and Propagation of Stress Corrosion Cracking in 304L Austenitic Stainless Steel

Despite the high corrosion resistance of austenitic stainless steels (SSs), a significant reduction of stress corrosion cracking (SCC) resistance has been reported in cases of high residual stress and metastable microstructural features. In this study, the effect of thermo-mechanical processing (TMP) on the initiation and propagation of SCC in 304L SS was studied. To better understand the SCC mechanisms, three TMPs conditions—welded, solution annealed at 1050 °C for tens of seconds, and straightened—were used. The research focused on analyzing the initial microstructure, residual stress, and hardness along the depth direction to assess SCC resistance and establish correlations with the observed SCC modes. Experimental results demonstrated that transgranular SCC was observed in regions exhibiting elevated residual stress induced by welding and straightening processes. Furthermore, the presence of strain-induced martensite transformation and slip bands formed during plastic deformation were identified as additional factors contributing to the susceptibility of SCC. The study findings highlighted that the magnitude and distribution of residual stresses, in conjunction with microstructural evolution, could be varied depending on the specific TMP condition, leading to different SCC susceptibilities, cracking modes, and directions.

Insights into the effects of δ-ferrite on crack tip stress/strain and stress corrosion cracking propagation behavior of austenite weld metal: A numerical and experimental study

The effects of δ-ferrite on stress corrosion cracking behaviors of austenite weld metal were analyzed by a ferrite-crack model. The results show that the δ-ferrite might inhibit the crack propagation initially once the crack tip meets it by reducing the local plastic strains. Thereafter, the crack might still propagate either along the δ-ferrite boundary (intergranular, IG) or across the δ-ferrite (transgranular, TG). The IG cracking will accumulate much more plastic strains at the crack tip and tends to promote crack growth. The TG cracking might be enhanced by the oxidation-induced embrittlement of the δ-ferrite.

Innovative prevention of stress corrosion crack propagation in nuclear power pipe welds

Abstract Failure caused by stress corrosion cracking (SCC) is inevitable during the long-term service of nuclear power pipe welds. This is mainly due to the propagation of microcracks in the deposited metal, which seriously affects the operation safety of nuclear power pressure pipes. Overlay welding is practical for pressure pipe repair welding, which can introduce compressive residual stress inside the weld seam. In this work, a diagonal T-pipe joint was fabricated using tungsten inert gas arc welding with ERRS-3 wire, and an overlay weld was also fabricated using tungsten inert gas arc welding with ERRS-3 wire under circumstances of water in the pipe and no water in the pipe. And then the contour method and finite element method were employed to measure and calculate the residual stress distribution in the diagonal T-pipe joint. Both results showed that overlay welding can introduce compressive residual stresses into the pipe joint. The compressive residual stress zone area inside the weld seam with water in the pipe is larger than that without water in the pipe, and the compressive residual stress zone area varies at different positions of the weld seam. This work is expected to promote the application of overlay weld technology in the diagonal T-shaped pipe joint repair and prevent stress corrosion crack propagation of nuclear power pipe welds.

Characterisation of stress corrosion durability and time-dependent performance of cable bolts in underground mine environments

Premature failures of cable bolt caused by stress corrosion cracking (SCC) has been more and more often observed with the increasing depth of underground mines. Investigating and predicting this failure are critical in maintaining and accessing the integrity of the reinforcement system. In this study, with application of the designed SCC-AE testing system, the SCC failure processes of cold-drawn cable bolts used in underground reinforcement system was investigated using the acoustic emission (AE) techniques in simulated underground conditions. Damage evolution of the specimens was monitored with AE in real-time. The scanning electron microscopy was adopted to examine the fractographic features of the failed specimen. Through the integrated analysis of specimens’ elongation, the evolution of acoustic activities and fractographic features, three different stages during SCC failure processes were determined including cracks initiation due to the local corrosion, cracks propagation characterised as tear ridges appearance and fast fracture failure evidenced by the shear lips. The parameters of elongations, AE signals in each failure stage were investigated and the SCC propagation rates were determined. As a result, this study confirms the AE technique in combination with the designed testing system can give important insights into the SCC failure as well as the possibilities of real-time SCC monitoring in underground reinforcement systems.

Stress corrosion cracking growth rate prediction model for nuclear power turbine rotor steel in a simulated environment

Considering the electrochemical reaction and chemical reaction near the crack in the local corrosion environment, the stress corrosion cracking growth rate prediction model for nuclear power turbine rotor steel was established based on the slip dissolution mechanism and finite element method. The calculated parameters were defined based on the material and electrochemical properties of steam turbine rotor in the simulated environment, and the calculated results can agree well with the experiment results. Results revealed that the stress intensity factor has an important influence on the local corrosion environment at the crack tip, the electrode potential is decreased and the process of anodic dissolution is accelerated with the increase of the stress intensity factor. Furthermore, the prediction model can describe stage-I and stage-II of stress corrosion cracking propagation well, and provide a possible trend prediction for practical production practice.

Nucleation and propagation of stress corrosion cracks: Modeling by cellular automata and finite element analysis

The stress corrosion cracking process of pipeline steel was modeled using cellular automata and finite element analysis, the initiation and propagation of the cracks were simulated. Before the initiation of cracks, the extent of pitting corrosion was revealed to be controlled by anodic reactions and mechanical factors, in which electrochemical corrosion played a leading role. The deposition of corrosion products created a diffusion barrier between the reactants participating in the corrosion process, limiting the rate of electrochemical reactions. During the crack propagation process, the mechanochemical effects caused by plastic deformation promoted anodic dissolution at the crack tip, driving crack propagation.

Stress corrosion characteristics of electron beam welded titanium alloys joints in NaCl solution

The Ti6321 titanium alloy has stress corrosion sensitivity in 3.5% NaCl solution, and the sample with cracks will fracture in a short time. The aim of this paper is to reveal the key factors affecting the stress corrosion resistance and clarify the stress corrosion mechanism of different regions of the joint by studying the crack propagation and stress corrosion critical stress intensity factor of the different regions of titanium alloy welded joint. Stress corrosion cracking, fracture and crack propagation path of electron beam welded titanium alloy joint were analyzed, characteristics of microstructure, texture and electrochemical were studied. The results indicated that the stress corrosion intensity factor KISCC of the weld metal is >76.50 MPa • m 1 / 2 , and the maximum KISCC value of heat affected zone is 51.62 MPa • m 1/2 , so KISCC of weld metal is better than heat affected zone. The crack growth rate of weld metal is slightly higher than that of heat affected zone. The fractured surface of weld metal has no obvious stress corrosion characterization, while heat affected zone has. The propagation path of weld metal is more zigzag than that of heat affected zone. The results reveal that microstructure, texture and electrochemical properties are the main reasons for stress corrosion. • The stress corrosion of titanium alloy electron beam welded joint in different regions has been studied. • The stress corrosion resistance of weld metal is significantly higher than heat affected zone, which is related to composition, microstructure and microtexture. • The stress corrosion crack mechanism of titanium alloy welded joint is the combined action of crack propagation and potential corrosion under stress.

Hydrogen effects on passivation and SCC of 2205 DSS in acidified simulated seawater

In this work, hydrogen effects on passivation and stress corrosion cracking (SCC) of 2205 duplex stainless steel (DSS) in acidified seawater were investigated. Results show hydrogen deteriorates passive film, accelerates localized anodic dissolution (AD) and causes hydrogen damage, leading to high SCC susceptibility by hydrogen embrittlement (HE) and hydrogen facilitated anodic dissolution (HFAD). SCC initiates in ferrite, and propagates as transgranular-SCC (TGSCC) and intergranular-SCC (IGSCC). When loaded along rolling direction (RD), hydrogen segregating in austenite hardens austenite during SCC propagation; while hydrogen enriching in ferrite causes hydrogen enhanced localized plasticity (HELP) effect for transverse direction (TD) load.

Real-time monitoring of stress corrosion cracking in 304 L stainless steel pipe using acoustic emission

A stress corrosion cracking (SCC) monitoring indicator (MI) based on the acoustic emission (AE) technique is proposed for the real-time detection and monitoring of SCC initiation in 304 L stainless steel (SS) pipes used for the primary circuits of nuclear power plants (NPPs). A device is used to accelerate the initiation of SCC to shorten the experiment timeframe. A non-crack AE signal criterion was established, which was conducted by injecting an etchant and distilled water into 304 L SS pipe specimens as experimental and control groups, respectively. Furthermore, to characterize the AE signal responsible for cracking, the characteristics of the AE signal measured in the section between necking and fracture (where cracks occur and propagate) among the stress curves obtained from the 304 L SS tensile test using AE sensors were investigated. Subsequently, the maximum amplitude, energy, frequency characteristics (range and magnitude), and waveform of the remaining AE signals were investigated after removing some AE signals by applying the non-crack AE signal criterion in the experiment where the SCC penetrated the pipe. These were compared with the maximum amplitude, energy, frequency characteristics, and waveform which were investigated in the tensile test to derive common characteristics for the two sets of crack signals to establish an SCC MI. To evaluate the performance of the developed SCC MI, the SCC monitoring experiment was halted when AE signals corresponding to the SCC MI criteria were measured, to fabricate a pipe wherein non-penetrating SCC was formed. In this manner, by applying the SCC MI to detect SCC in real time, we verified that the SCC MI had excellent SCC detection performance. Furthermore, we performed scanning electron microscopy (SEM) image analyses and SEM-energy dispersive X-ray spectrometry analyses to investigate the causes of SCC propagation.

A Review of Factors Affecting SCC Initiation and Propagation in Pipeline Carbon Steels

Pipelines have been installed and operated around the globe to transport oil and gas for decades. They are considered to be an effective, economic and safe means of transportation. The major concern in their operation is corrosion. Among the different forms of corrosion, stress corrosion cracking (SCC), which is caused by stresses induced by internal fluid flow or other external forces during the pipeline’s operation, in combined action with the presence of a corrosive medium, can lead to pipeline failure. In this paper, an extensive review of different factors affecting SCC of pipeline steels in various environmental conditions is carried out to understand their impact. Several factors such as temperature, presence of oxidizers (O2, CO2, H2S, etc.), composition and concentration of medium, pH, applied stress, and microstructure of the metal/alloy have been established to affect the SCC of pipeline steels. SCC susceptibility of a steel at a particular temperature strongly depends on the type and composition of the corrosive medium and microstructure. It was observed that pipeline steels with water quenched and quenched and tempered heat treatments, such as those that consist of acicular ferrite or bainitic ferrite grains, are more susceptible to SCC irrespective of solution type and composition. Applied stress, stress concentration and fluctuating stress facilitates SCC initiation and propagation. In general, the mechanisms for crack initiation and propagation in near-neutral solutions are anodic dissolution and hydrogen embrittlement.

Stress corrosion crack initiation and propagation before proceeding to Stage 2 for hydrostatically tested pipeline steels

Stress corrosion crack initiation and propagation before proceeding to Stage 2 for hydrostatically tested pipeline steels