Stress Corrosion Cracking Mechanism Research Articles

New insights into stress corrosion cracking mechanism of Alloy 600 in boiling water reactor (BWR) environment

Several mechanisms have been proposed to explain the intergranular stress corrosion cracking (IGSCC) of Alloy 600 in BWR, but slip-dissolution at grain boundaries remains the most recognized cause. However, it is still uncertain whether the above degradation is accompanied by selective internal oxidation (SIO) as a precursor. Following new insights into the creviced bent beam (CBB) test, relevant evidence was discovered. Additionally, the results of First Principle Calculation indicate interstitial O actively competes for chromium in IG carbides to form chromium oxides during the SIO process, instead of passively waiting for the oxidation/decomposition of carbides to provide a chromium source.

Stress corrosion cracking behavior and mechanism of 2205 duplex stainless steel under applied polarization potentials

In this work, a non-steady electrochemical model for assessing stress corrosion cracking (SCC) of 2205 duplex stainless steel (DSS) under applied polarization potentials was proposed, and the SCC mechanism was revealed. With the negative shift of potentials, hydrogen enhances SCC susceptibility by deteriorating passive film, inhibiting repassivation and causing serious damage. In particular, at −850 mV (vs. SCE), the synergetic effect of anodic dissolution (AD) and hydrogen embrittlement (HE) causes severe pitting and SCC. The negative shift of applied potentials changes the preferential pit/SCC initiation site due to high hydrogen concentration in austenite.

Study of stress corrosion cracking susceptibility of irradiated ferrite-martensitic stainless steel 07Kh12NMFB in supercritical water. Part 2. Development of corrosion crack identification technique and analysis of autoclave test results

The studies of stress corrosion cracking have been carried out for the stainless ferritic-martensitic steel with chromium content of 12% irradiated to a damage neutron dose of ~12 dpa. This steel was chosen as a candidate material for the internals of supercritical water-cooled reactors (SWCR).The first part of the paper was devoted to autoclave testing of specially designed disk specimens under constant load in a supercritical water environment (at 450°C and 250 atm pressure). In this part of the article the developed technique for corrosion cracks identification is presented and analysis of autoclave tests results is performed.As a result of the experiments performed, the threshold stress values below which stress corrosion cracking initiation doesn’t occur. The values of threshold stresses are determined for the studied steel irradiated at temperatures of 390 and 550°C. Possible mechanisms of stress corrosion cracking of the studied steel are analyzed and directions for further research are proposed.

In vitro evaluation of stress corrosion cracking susceptibility of PEO-coated rare-earth magnesium alloy WE43

Controlling material degradation in complex mechanobiological environments is the current challenge in advancing biodegradable magnesium implants for orthopaedic applications. Understanding stress corrosion cracking (SCC) mechanisms of magnesium alloy-coating systems in physiological fluids facilitates the design of magnesium implants with excellent biomedical performance. In this study, we investigated the SCC behaviour of a medical grade PEO-coated magnesium alloy WE43 under different loading conditions. Constant loadings tests (CLT) and slow strain rate tests (SSRT) were conducted to evaluate the SCC susceptibility of this alloy-coating system under in vitro conditions. Fracture surfaces of the non-coated and PEO-coated specimens were characterised by scanning electron microscopy to reveal the SCC mechanisms under different loading configurations. The experimental results showed that the alloy-coating system exhibits a high SCC resistance in SSRT conditions. However, high stress levels and plastic deformations lead to a significant acceleration of the SCC process. Moreover, the fracture surface analysis demonstrated that the brittle nature of the PEO coating deteriorates the mechanical integrity of the alloy under critical mechanical loadings, which results in an increased susceptibility towards stress corrosion cracking of the coated WE43.

Data Mining Applied to the Electrochemical Noise Technique in the Time/Frequency Domain for Stress Corrosion Cracking Recognition

In this paper, time/frequency domain data processing was proposed to analyse the EN signal recorded during stress corrosion cracking on precipitation-hardening martensitic stainless steel in a chloride environment. Continuous Wavelet Transform, albeit with some limitations, showed a suitable support in the discriminatory capacity among transient signals related to the different stress corrosion cracking mechanisms. In particular, the aim is to propose the analysis of electrochemical noise signals under stress corrosion cracking conditions in the time–frequency domain by using the Hilbert–Huang approach. The Hilbert–Huang Transform (performed by the Empirical Mode Decomposition approach) was finally proposed to carry out an identification of the corrosion mechanisms in comparison to conventional data processing methods. By using this approach, a detailed simultaneous decomposition of the original electrochemical noise data in the time and frequency domain was carried out. The method gave useful information about transitions among different corrosion mechanisms, allowing us to (i) identify a specific characteristic response for each corrosion damaging phenomenon induced by stress corrosion cracking, (ii) time each corrosion of the damaging phenomenon, and (iii) provide a topological description of the advancing SCC damaging stages. This characteristic evidences that the Hilbert–Huang Transform is a very powerful technique to potentially recognize and distinguish the different corrosion mechanisms occurring during stress corrosion cracking.

Influence of AC/DC on stress corrosion cracking of Ti-6Al-3Nb-2Zr-1Mo alloy in simulated marine solution

The study investigated the influence of alternating current (AC) and direct current (DC) on stress corrosion cracking (SCC) behavior of Ti-6Al-3Nb-2Zr-1Mo (Ti80) alloy in simulated marine solution with different pH levels. Electrochemical measurements, slow strain rate tensile (SSRT) tests and fracture morphology analysis were used to evaluate SCC behavior. Under conditions of pH = 2 or 1, AC enhances SCC susceptibility by disrupting the passive film, primarily attributed to anodic dissolution and hydrogen embrittlement. When both AC and DC coexist, the excessively negative potential intensifies the hydrogen evolution reaction, leading to hydrogen embrittlement dominating the SCC mechanism of Ti80.

Understanding the non-steady electrochemical mechanism on SCC of 304 SS under applied polarization potentials

In this work, the non-steady electrochemical model on stress corrosion cracking (SCC) was established, which was verified by SCC of 304 SS with various microstructures. SCC mechanism depends on applied potentials including anodic dissolution (AD), hydrogen embrittlement (HE) and AD+HE, and the potential range for each mechanism was determined with the critical potentials on slow/fast scan potentiodynamic curves. The quantitative relationship of SCC susceptibility and applied potentials is acquired with the model, which is effective for assessing SCC. It was verified by 304 SS with various microstructures, which presents similar non-steady electrochemical characteristics and SCC susceptibility.

Effect of low dose irradiation of heavy ion on electrochemical corrosion and IASCC behavior of austenitic steel

The impacts of low dose irradiation on the behavior of electrochemical corrosion and irradiation assisted stress corrosion cracking for 321 stainless steel were studied using Fe2+ ion irradiation to simulate neutron radiation damage in primary circuit environment of pressurized water reactor. Low dose irradiation can improve the pitting resistance and reduce the cracking tendency of the alloy in B-Li solution to a certain extent, which was related to the δ phase content on the near-surface of the sample: The higher δ phase content on the near-surface of the 2 dpa irradiated sample was observed by grazing incident X-ray diffraction. In addition, the pits was significantly increased near micro-cracks for the unirradiated sample, indicating that the existence of pits induced the initiation of cracks. The research results provided an important reference for the failure mechanism of irradiation assisted stress corrosion cracking of core components.

Effect of alternating current on the electrochemical behavior and stress corrosion cracking of TA2 in simulated marine environment

This study investigated the effect of alternating current (AC) on the electrochemical and stress corrosion cracking (SCC) behavior and mechanism of TA2 in a simulated marine solution. The increase in the open circuit potential and charge transfer resistance indicated that the passivation film remained undamaged by varying AC densities, indicating a low risk of SCC. However, under the synergistic effect of AC and direct current (DC), the potential significantly shifted negatively, leading to hydrogen evolution reactions and the formation of a hydride layer. This hydride-induced hydrogen embrittlement posed a potential risk to the integrity of TA2.

Stress corrosion cracking behavior on carbon steel under the synergistic effect of chloride and bicarbonate ions in alternating wet-dry environment

The stress corrosion cracking mechanism of X80 carbon steel under the combined actions of chloride and bicarbonate ions in alternating wet-dry environment was investigated by performing slow strain rate tensile test and in-situ electrochemical detection during the SCC process under constant load. The results showed that the oxidation and reduction reaction cycle of iron oxide during wet-dry cycle would accelerate the corrosion process. The pitting under the corrosion product layer at high concentrations of chloride and bicarbonate was the origin of SCC under the action of stress concentration, which made steel display high SCC susceptibility.

Improving Corrosion and Stress Corrosion Cracking Performance of Machined Biodegradable Alloy ZX20 by HF-Treatment

The treatment with hydrofluoric acid (HF-treatment) was suggested to be an effective way of improving the corrosion resistance of Mg alloys, including Mg-Zn-Ca (ZX) ones used for biodegradable implants. However, the effect of the HF-treatment on the stress corrosion cracking (SCC) susceptibility of ZX alloys has not been reported yet, although this phenomenon can induce premature brittle failures of the metallic medical devices, and thus, it is critical for their in-service structural integrity. In the present study, the effect of the HF-treatment on the microstructure, cytotoxicity, corrosion rate, mechanical properties, and fracture and side surface characteristics of the as-cast ZX20 alloy were investigated with the use of scanning electron microscopy, immersion, and slow-strain rate tensile testing in Hanks’ solution and indirect cell viability tests. It is found that the HF-treatment exerts no cytotoxic effect and results in a significant reduction in corrosion rate (up to 6 times of magnitude) and SCC susceptibility indexes (up to 1.5 times of magnitude). The observed improvement of corrosion and SCC performance of the alloy by the HF-treatment is found to be attributed to three effects, including (i) formation of the protective surface film of MgF2, (ii) removal of surficial contaminations originating from sample preparation procedures, and (iii) dissolution of surficial secondary phase particles. The mechanism of corrosion and SCC in the specimens before and after the HF-treatment are discussed.

The synergistic effect of parallel magnetic field and sulfate-reducing bacteria on stress corrosion cracking of buried X80 pipeline steel

In this work, the synergistic effect of parallel magnetic field and sulfate-reducing bacteria (SRB) on stress corrosion cracking (SCC) of X80 pipeline steel in buried soil environments was investigated for the first time by electrochemical experiments, slow strain rate tensile tests (SSRT) and surface characterization. The results showed that the parallel magnetic field suppressed electrochemical corrosion in a sterile environment; the SCC susceptibility decreased with increasing magnetic field strength (0–100 mT). The magnetic field and SRB synergistically promoted the formation of a dense film layer on the surface of the specimen in the inoculated SRB environment. The dense film layer suppresses the local corrosion of the metal and therefore the SCC susceptibility is reduced. The suppression effect no longer increased significantly when the magnetic field strength reached 75 mT. The synergy between the parallel magnetic field and the SRB was responsible for the reduced susceptibility of the SCC. This work contributed to a more in-depth study of the mechanisms of pipeline SCC and the development of pipeline SCC prevention technologies.

Stress corrosion cracking failure of X80 carbon steel U-bend caused by Desulfovibrio vulgaris biocorrosion

Sulfate reducing bacteria (SRB) are widely present in oil and gas industry, causing pitting corrosion on pipeline steel. Stress corrosion cracking (SCC) often occurs in the presence of mechanical stress before pitting perforation failure, leading to economic losses and even catastrophic accidents. In this study, stress distribution simulation using the finite element method (FEM), corrosion analysis techniques and electrochemical corrosion measurements were employed to investigate the SCC mechanism of X80 pipeline steel caused by Desulfovibrio vulgaris, which is a common SRB strain used in microbiologically influenced corrosion (MIC) studies. It was found that D. vulgaris MIC caused sharp microcracks on an X80 U-bend coupon after only 2 weeks of immersion at 37 °C in the deoxygenated ATCC 1249 culture medium inoculated with D. vulgaris. The X80 U-bend coupon's weight loss-based uniform corrosion rate for the 12 cm2 surface was 60% of that for the unstressed flat square coupon (2.3 mg cm−2 vs. 3.8 mg cm−2). This was likely because the square coupon had wide MIC pits, providing a larger effective surface area for more sessile cells (4.2×108 cells cm−2 on square coupon vs. 2.4×108 cells cm−2 on U-bend coupon) to attach and harvest more electrons. An SCC failure occurred on an X80 U-bend pre-cracked at the outer bottom after a 6-week immersion in the D. vulgaris broth. Apart from MIC damage, this could also be because D. vulgaris metabolism increased the availability hydrogen atoms on the steel surface, and promoted the diffusion of hydrogen atoms into the metal lattice, thus increasing the brittleness of the steel.

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.

Effect of Ti on stress corrosion cracking behavior and mechanism of Monel K500 alloy in flowing seawater

Purpose The purpose of this paper is to investigate the effect Ti on stress corrosion cracking (SCC) and flow accelerated stress corrosion cracking (FA-SCC) behavior and mechanisms of Monel K500 alloy. Design/methodology/approach Monel K500 alloy with different Ti contents was designed. A metallurgical microscope (XJP-3C) and scanning electron microscopy (EV0 MA15 Zeiss) with an energy dispersive spectroscopy were used to analyze the microstructure of the Monel K500 alloy. In situ electrochemical tests were carried out in static and flowing seawater to study FA-SCC behavior. Findings The number of TiCN particles in the alloy increased as the increase of Ti content. The static corrosion and SCC of Monel K500 alloy are reduced as the content of Ti increases. Generally, the SCC of alloys was caused by the synergistic effect of the anodic dissolution at exposed metal matrix and the pit corrosion of metal matrix adjacent to TiCN particles, which was further accelerated by flowing. Originality/value The corrosion behavior and mechanism of Monel K500 alloy with different Ti contents in a complex flowing seawater environment are still unclear, which remain systematic study to insure the safe service of the alloy.

A mechanistic study on dealloying-induced stress corrosion cracking of Alloy 800 in boiling caustic solutions

Alloy 800 (Fe-30Ni-20Cr) is used in steam generators of some nuclear power plants. In-service performance has been excellent, but stress corrosion cracking (SCC) can occur in certain off-chemistry environments. In this study, the SCC mechanism for Alloy 800 in boiling caustic solution is investigated. After exposure, a Ni-rich porous surface film is formed with a large density of cracks. Complementary electron microscopy techniques are applied to study the SCC mechanism at the nanoscale from chemical and mechanical perspectives. Results suggest SCC initiation occurs by transmission of a micro-crack from the Ni-rich layer into the substrate material via a cleavage mechanism.

Analysis of Cracks of Thermostats Casings Made of Brass

As part of the project “Thermostat for universal use in (electro) mobility”, an analysis of three currently used thermostats failed during operation was performed. In all three cases, cracks occurred in the brass outer casings. The cracks were open and fractographical observation was performed. The microstructure of the material was evaluated using both the light and scanning electron microscopy. The local composition of the material was determined by EDS microanalysis. Furthermore, hardness profiles were measured. The cracks were predominantly intergranular with a smaller portion of transgranular cleavage. The microstructure was formed by a mixture of α- and β-phase grains and lead particles. In addition to the stress caused by the overpressure of the molten wax, a higher level of residual stresses caused by deformations can be expected. The failure was caused by the mechanism of stress-corrosion cracking. Metal induced embrittlement or/and corrosion fatigue could interact too.

Stress Corrosion Cracking Mechanisms of UNS S32205 Duplex Stainless Steel in Carbonated Solution Induced by Chlorides

Herein, the chloride-induced stress corrosion cracking (SCC) mechanisms of UNS S32205 duplex stainless steel (DSS) reinforcing bars in alkaline and carbonated solutions are studied. Electrochemical monitoring and mechanical properties were tested using linear polarization resistance and electrochemical impedance spectroscopy, coupled with the slow strain rate tensile test (SSRT) to evaluate the SCC behavior and unravel the pit-to-crack mechanisms. Pit initiation and crack morphology were identified by fractographic analysis, which revealed the transgranular (TG) SCC mechanism. HCO3− acidification enhanced the anodic dissolution kinetics, thus promoting a premature pit-to-crack transition, seen by the decrease in the maximum phase angle in the Bode plot at low frequencies (≈ 1 Hz) for the carbonated solution. The crack propagation rate for the carbonated solution increased by over 100% compared to the alkaline solution, coinciding with the lower phase angle from the Bode plots, as well as with the lower charge transfer resistance. Pit initiation was found at the TiN nonmetallic inclusion inside the ferrite phase cleavage facet, which developed TG-SCC.

Scanning Kelvin Probe for Detection in Steel of Locations Enriched by Hydrogen and Prone to Cracking

Hydrogen, due to corrosion processes, can degrade high strength steels (HSS) through embrittlement and stress corrosion cracking mechanisms. Scanning Kelvin probe (SKP) mapping of surface potential was applied, to visualize the locations with an increased subsurface concentration of hydrogen in mild steel and martensitic HSS. This work can help to determine the reasons behind hydrogen localization in a steel microstructure, leading to embrittlement and hydrogen-assisted cracking. Cathodic charging was used to insert hydrogen, which decreased the steel potential. Hydrogen effusion in air passivates steel, increasing the potential of HSS and mild steel. The passivation of steels was monitored depending on different conditions of cathodic pre-charging and the amount of absorbed hydrogen. The SKP could determine the area of diffusible hydrogen and the area of cracks. In addition, low potential locations linked to the hydrogen trapped in the deformed HSS microstructure were also determined, which delayed the steel passivation. Mild steel showed a uniform potential distribution related to interstitial hydrogen, without potential extremes attributed to locally accumulated hydrogen. Thus, SKP sensing can detect locations containing increased concentrations of hydrogen and sensitive to steel cracking.

Failure analysis of S13Cr-110 telescopic tube used in an ultra-deep gas well

The failure reason and stress corrosion cracking mechanism of S13Cr-110 telescopic tube used in an ultra-deep gas well are discussed based on physical and chemical properties, operating conditions and construction processes. The results show that: stress corrosion cracking occurred in S13Cr-110 telescopic tube during acid fracturing, the crack initiated from the bottom of the corrosion pit in the inner wall of the telescopic tube and the crack propagation mode is inter-granular cracking. The reason for cracking is that S13Cr-110, the telescopic tube material, is exposed to high-chlorine-containing acid environment for a long time in the acid fracturing process, and the corrosion inhibitor used at the temperature of ultra-deep well has poor corrosion inhibition effect, resulting in inter-granular crack originated from the bottom of the corrosion pit on the inner wall of the telescopic tube. During the subsequent acidizing operations, the telescopic tube sustained a high circumferential tensile stress, stress corrosion occurs, and the stress corrosion cracks expand rapidly. It is suggested that the S13Cr-110 pipe string used in acidic environments with high chloride concentrations should be selected with appropriate corrosion inhibitor based on well depth and formation temperature.