Stress Corrosion Cracking Mechanism Research Articles

Effects of thermal aging on the stress corrosion cracking behavior of cast stainless steel with different δ-ferrite levels in high temperature water environment

This study focused on the combined effect of ferrite content and thermal aging on the stress corrosion cracking (SCC) of CF8A by using an alternating current potential drop (ACPD) technique to measure the SCC growth rates in high temperature water environment. The results show that thermal aging and high δ-ferrite content increased the susceptibility to SCC. The SCC susceptibility to the factor of δ-ferrite content of CF8A is greater than that for thermal aging treatment. Furthermore, the SCC mechanisms at the crack tip were investigated using transmission electron microscopy (TEM). The formation of Fe oxide ahead of the crack tip enhanced the crack propagation along γ / δ-ferrite interface. For the specimen with high δ-ferrite content, the δ-ferrites were distributed in continuous networks, which provide continuous SCC-sensitive paths.

Effect of annealing time on the microstructure and SCC behavior of an austenite-based low-density steel in a marine atmosphere

The microstructure and stress corrosion cracking (SCC) behavior of the Fe-Mn-Al-C-Ni low-density steels (LDSs) with different annealing times were studied in a simulated marine atmosphere, and the relation between them was discussed. The results indicated that the SCC mechanism of the LDSs was a combination of anodic dissolution and hydrogen embrittlement. This behavior was greatly facilitated by a micro-galvanic corrosion effect between B2 phase and austenite. The SCC resistance of the LDSs increased gradually as the annealing time extended, attributing to the transformation of B2 band to B2 particle, the decrease in the potential difference, and the homogenization of the strain distribution.

Susceptibility of Dissimilar IN600 Welded Joints to Stress Corrosion Cracking Using Slow Strain Rate Test in Sodium Electrolytes

The stress corrosion cracking (SCC) behavior of aged plates of Inconel 600 welded to Inconel 600 plates in the as-received condition was studied using the slow strain rate test (SSRT) in two sodium containing electrolytes at 25 and 80 °C. The aged plate was used to simulate damage by the operation service. Electrochemical noise (EN) was used to monitor the SCC. The plates were gas metal arc welded (GMAW) employing ERNiCrMo-3 and ER310 filler wires along with 95% Ar + 3% N2 + 2% O2 and 97% Ar + 3% N2 as the shielding gas, respectively. The microstructure of the welded joints was characterized using optical and scanning electron microscopy. The results of the SCC revealed that when sodium thiosulfate was used, the loss in plasticity was higher in the NiCrMo-3 joint with around a 20 percent decrease. Conversely, in the 310 welds, the loss in plasticity was higher in the sodium hydroxide, which diminished by 12 percent. A few secondary microcracks were observed in the transversal section in specimens of both welds. The results of the EN showed an increase in the potential and current when the sample reached the tensile strength and then decreased when the neck was formed; these changes indicate that some events occurred during the SSRT. The EN data showed two types of corrosion: general corrosion for NiCrMo-3 and mixed corrosion for the 310 welded joint in both environments. Electrochemical polarization was also employed to understand the mechanism of SCC.

Advanced microstructural characterization of transgranular Pb-caustic SCC in Alloy 690TT

Alloy 690TT was tested at 340 °C in mildly caustic environments containing lead (Pb) to investigate the transgranular cracking mechanism of Pb-induced stress corrosion cracking (PbSCC). Advanced electron microscopy characterization revealed that the fracture surfaces exhibited evidence of cleavage and regions with significant enrichment of metallic Ni, which maintained the same orientation as the original grain matrix. Moreover, there are some indications that crystallographic cracking along {100} and {110} planes is possible at high pH in Pb-containing environment. These experimental observations are consistent with a form of film-induced cleavage mechanism, assisted by de-alloying and exacerbated by planar slip in the matrix.

Stress corrosion cracking mechanism of cold spray coating on a galvanically similar substrate

The chloride-induced stress corrosion cracking (CISCC) mechanism of cold spray (CS) coating on a galvanically similar substrate is investigated. Arc welded 304L stainless steel (SS) specimens are loaded into four-point bend fixtures, cold sprayed with 304L SS, then immersed in boiling MgCl2. Interconnected porosity forms through crevice corrosion along CS splat boundaries, allowing corrosive species to penetrate through the CS layer. Nevertheless, the substrate is resistant to CISCC likely because of compressive stress introduced by peening during CS particle impacts. These findings underscore the importance of residual stress in the environmental degradation of CS coatings or repairs of engineering structures.

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.

Methods of corrosion testing used for development and commercial exploitation of new shipbuilding steels and alloys. Review. Part II. Corrosion cracking and field marine tests

The review describes methods of stress corrosion cracking (SCС) tests that implement various conditions for samples loading: at a constant static load or deformation, at a constant or increasing load of samples with a previously grown fatigue crack, with a slow strain rate. Such tests shall be carried out to determine the resistance of shipbuilding materials to be used in loaded ship structures in contact with seawater. Brief descriptions of the mechanism of stress corrosion cracking of steels and alloys are given. The necessity to carry out bench tests of steels and their welded joints, as well as models simulating individual units and elements of structures, is indicated. At this stage, conditions are ensured as close to operating conditions as possible due to exposure in various climatic zones of the world’s oceans (variations in temperature, chloride concentration, amount of dissolved oxygen, degree of biofouling, and their simultaneous impact). It is shown that during verification field tests (final stage) new materials promising for operation in marine conditions pass the final evaluation of corrosion resistance in the form of elements of ship structures and systems in the conditions of ship operation.

Influencing factors and mechanism of iodine-induced stress corrosion cracking of zirconium alloy cladding: A review

Influencing factors and mechanism of iodine-induced stress corrosion cracking of zirconium alloy cladding: A review

Hydrogen trapping by irradiation-induced defects in 316 Lstainless steel: A combined experimental and modeling study

The irradiation-induced defects in stainless steel internal components of pressurized water reactors combined with hydrogen uptake during the oxidation process could be a key parameter in the mechanism for Irradiation-Assisted Stress Corrosion Cracking (IASCC). A heat-treated 316 L SS containing a low amount of defects was Fe3+ ions-implanted; irradiation-induced defects types and depth distributions were characterized by Transmission electron microscopy (TEM). Deuterium was then inserted in the specimens either by cathodic charging or by sample exposure to deuterated primary water. Secondary Ions Mass Spectrometry – SIMS – permitted to access the deuterium distribution at the implanted stainless steel surface. A finite difference numerical solver accounting for hydrogen diffusion/trapping coupling was used to simulate the hydrogen transport in the implanted material, taken into consideration the specific heterogeneous character of the irradiation-induced defects distribution in matter. Taking as input data the experimental defects distribution associated with Frank loops or voids, the main trapping sites for hydrogen were assigned to voids, not Frank loops. Such numerical approach was able to deal accurately with the problem of hydrogen transport in a heterogeneous material as well as to differentiate two potential trap sites contributions to the experimental deuterium distribution. In addition, according to results obtained after primary water exposure, trapping at voids was still effective at 320 °C, signature of a high binding energy of hydrogen in voids.

Анализ влияния предела текучести на коррозионное растрескивание под напряжением мартенситных и ферритных сталей в кислых средах

To evaluate the effect of yield stress on hydrogen embrittlement (HE) of martensitic and ferritic steels, the effect of hydrogen (H) capture by structural inhomogeneities (hydrogen traps) and the effect of plastic deformation and stress on the mechanism of stress corrosion cracking (SCC) are considered. In the presence of hydrogen, the brittle fracture of high-strength martensitic steels consists of flat areas of intergranular fracture at the initial austenitic grain boundaries and quasi-brittle cracks at the boundaries of martensite blocks. In low-strength steels, brittle fracture manifests itself in the form of transgranular fracture of ferrite grains. The decrease in the characteristics of martensitic steels with an increase in the yield strength occurs due to an increase in the hydrogen concentration at the stage of anodic dissolution (AD) due to the growth of the carbide/matrix interface. The reason for the growth hydrogen concentration in ferritic steels is a large mechanical overstress, an increase in the number of active dissolution centers, the formation of an electrochemical pearlite-ferrite pair, and an increase in surface roughness with increasing deformation. It is concluded that the bell-shaped dependences of the critical stress of the transition from AD to SCC and other characteristics of mechanical tests on magnitude are due to different mechanisms of hydrogen accumulation in martensitic and ferritic steels.

Analysis of the effect of yield stress on stress corrosion cracking of martensitic and ferritic steels in acidic environments

To evaluate the effect of yield stress on hydrogen embrittlement (HE) of martensitic and ferritic steels, the effect of hydrogen (H) capture by structural inhomogeneities (hydrogen traps) and the effect of plastic deformation and stress on the mechanism of stress corrosion cracking (SCC) are considered. In the presence of hydrogen, the brittle fracture of high-strength martensitic steels consists of flat areas of intergranular fracture at the initial austenitic grain boundaries and quasi-brittle cracks at the boundaries of martensite blocks. In low-strength steels, brittle fracture manifests itself in the form of transgranular fracture of ferrite grains. The decrease in the characteristics of martensitic steels with an increase in the yield strength occurs due to an increase in the hydrogen concentration at the stage of anodic dissolution (AD) due to the growth of the carbide/matrix interface. The reason for the growth hydrogen concentration in ferritic steels is a large mechanical overstress, an increase in the number of active dissolution centers, the formation of an electrochemical pearlite-ferrite pair, and an increase in surface roughness with increasing deformation. It is concluded that the bell-shaped dependences of the critical stress of the transition from AD to SCC and other characteristics of mechanical tests on magnitude of the yield stress are due to different mechanisms of hydrogen accumulation in martensitic and ferritic steels. Keywords: hydrogen embrittlement, high-angle boundaries, interfaces, traps, hydrogen binding energy, structural inhomogeneities, fracture.

METHODICAL APPROACH TO THE STUDY OF STRESS CORROSION CRACKING MECHANISM OF PIPELINE STEEL AT CATHODIC PROTECTION BY LINEAR SWEEP VOLTAMETRY

A methodological approach to the rapid assessment by linear sweep voltammetry method stress corrosion cracking (SCC) mechanism of pipeline steels of various grades under cathodic protection has been developed. The proposed approach serves as the basis for the electrochemical study of the mechanism of stress corrosion cracking of pipeline steel at various protective potentials for laboratory conditions. The ratio of polarization currents at fast () and slow () scanning potential rate was determined, its analysis was carried out depending on the polarization potential for steels of various grades. It was established that polarization potentials at which the difference between corrosion rate of the crack’s tip and the other surface is the maximum (maximum value of ) and the rapid development of stress corrosion cracks begin, which is differ for steels of various grades and equal near -0.75 V for X70 steel, -0.85 V for 09G2S steel and -0.8 V for 17G1S steel. The boundaries of the polarization potentials are established, beyond which the SCC mechanism of the investigated steels in the model soil environment NS4 changes, namely: from -0.75 V to -1.05 V for X70; -0.85 V to -1.0 V for 09G2S; from -0.8 V to -0.98 V for 17G1S. This indicates the possibility of SCC development with different rates and patterns, all other things being equal. The results of the work can be useful both for a theoretical understanding of the SCC mechanism and for an express assessment of the SCC mechanism in a soil environment and, in particular, in underfilm electrolyte under a disbanded coating.

Investigating the mechanism of stress corrosion cracking of controllable rolling pipe steel X70 in near-neutral environment

The results of investigating the mechanism of stress-corrosion cracking of a controllable rolling pipe steel X70 at a cathodic protection in near-neutral pH environment, using slow strain rate tests and polarization curves, are presented. Using the method of polarization curves, a critical range of potentials, namely, from −0.75 VAg/AgCl to −0.97 VAg/AgCl was determined, in which the steel stays in a non-equilibrium electrochemical state and anodic dissolution proceeds simultaneously with hydrogen reducing. It has been shown that in this range, the sensitivity of X70 steel to a stress-corrosion cracking is observed, which correlates with the loss of plastic properties and the appearance of a brittle component in the fracture. At the potential of −2.0 VAg/AgCl, the predominant cathodic reaction is hydrogen reducing at the tip of a crack and its walls. Here, the brittle fracture dominates, which correlates with the character of the fracture.

Effect of pre-strain and quench rate on stress corrosion cracking resistance of a low-Cu containing Al–Zn–Mg–Cu alloy

The synergy effect of quench rate and pre-strain prior to artificial aging heat treatment on microstructure, stress corrosion cracking (SCC) resistance, and mechanical property of a low-Cu containing Al–Zn–Mg–Cu alloy have been investigated using SCC and room temperature tensile tests, combined with X-ray diffraction, scanning electron microscopy (SEM), and high-angle angular dark-field scanning transmission electron microscopy (HAADF-STEM) microstructural examinations. The results showed that the SCC resistance was significantly improved by pre-strain and slow quench-rate owing to discontinuous distribution, large inter-space, and high Cu content of grain boundary precipitates. Moreover, the pre-strain was more effective for fast-quenched samples on improving SCC resistance compared with slowly quenched samples. The SCC mechanisms have been discussed in detail.

Intergranular SCC mechanism of ultrasonic nanocrystalline surface modified AISI 304 SS in H2SO4 solution containing chloride

In this work, the stress corrosion cracking (SCC) susceptibility of AISI 304 stainless steel processed using ultrasonic nanocrystalline surface modification (UNSM) treatment, was studied in 1 M H2SO4 containing 5 wt.% NaCl by means of combined slow strain rate test with electrochemical methods. The mechanical properties are improved by the UNSM, however the time to failure decreases due to the higher anodic dissolution kinetics of the UNSM sample, which remain in the order of mA/cm2 compared to µA/cm2 of the as-received (AR) sample. Adsorption of chloride ions has been identified by the presence of an inductive loop in the Nyquist plot, indicating a more reactive surface of the UNSM sample, which promotes dealloying of the metal. The development of several transgranular SCC (TG‒SCC) areas in the UNSM sample, compared to the AR, plus the nucleation of intergranular SCC (IG‒SCC) in the UNSM region is studied by scanning electron microscopy (SEM), X-ray micro-computed tomography (micro-CT), and electron back scattered diffraction (EBSD).

Mechanisms of Stress Corrosion Cracking of Irradiated Austenitic Chromium–Nickel Steels Used for WWER and PWR Vessel Internals

Mechanisms of Stress Corrosion Cracking of Irradiated Austenitic Chromium–Nickel Steels Used for WWER and PWR Vessel Internals

On the role of intergranular nanocavities in long-term stress corrosion cracking of Alloy 690

The life extension of nuclear power plants beyond 60-years relies on the integrity of the steam generator tubes during the extended life. Alloy 690 steam generator tubes have been generally believed to be resistant to stress corrosion cracking (SCC) failures until the recent unexpected observation of intergranular cavities during long-term SCC testing. Here, a multi-technique characterisation approach has been used to study the behaviour of 30% cold worked samples exposed to long-term SCC testing at constant load. This has provided quantitative results on the effect of intergranular cavities and oxidation ahead of the crack tip. SCC mechanisms of creep cavity formation and associated oxidation through the cavity networks are discussed and the required stress to failure calculated, providing a quantitative measure of their weakening effect and a reliable way of assessing and predicting this important degradation problem.

Stress corrosion cracking behavior induced by Sulfate-reducing bacteria and cathodic protection on X80 pipeline steel

Oil and gas pipelines with cathodic protection (CP) are often affected by Sulfate-reducing Bacteria (SRB), so it is of great relevance to understand the effect of SRB and CP potentials on the stress corrosion cracking (SCC) behavior of pipeline steel. In this paper, the SCC mechanisms in SRB-inoculated and sterile near-neutral soil environments were investigated at different CP potentials. Electrochemical tests and slow strain rate tensile tests showed that at −850 mV the pipeline steel was in a cathodic protected state. At −1000 mV and −1200 mV, strong cathodic polarization promotes the hydrogen evolution reaction, while SRB not only promotes pitting to provide a basis for crack nucleation, but also has a poisoning effect. The results show that the strong cathodic polarization potential and SRB increase the SCC susceptibility of pipeline steel and the hydrogen embrittlement (HE) risk.

Stress corrosion cracking behavior and mechanism of super 13Cr stainless steel in simulated O2/CO2 containing 3.5 wt% NaCl solution

Good CO2 corrosion resistance has made super 13Cr martensitic stainless steel become widely used in oil industry. However, the corrosion of OCTG (Oil CountryTubular Goods) changes from pure CO2 to O2/CO2/Cl- and other multi-component containing complex environment. To clarify the stress corrosion cracking (SCC) behavior and fracture mechanism of the super 13Cr stainless steel in the corrosive environment containing O2, CO2 and Cl-, the effect of applied potential on the SCC susceptibility of super 13Cr stainless steel in a 10% O2 and 90% CO2 containing 3.5 wt% NaCl solution was investigated by means of potentiodynamic polarization, slow strain rate tensile (SSRT) test and combined with scanning electron microscopy (SEM). The results show that the polarization potential has an influence on the SCC susceptibility of super 13Cr stainless steel in O2/CO2/Cl- containing medium. The SCC susceptibility is high with the anode and cathode polarization applied, and increases with the rise of theabsolute potential values. The SCC mechanism has the following relationships with the applied potentials: a) anodic dissolution happens at 50 mV and 250 mV, b) anodic dissolution and hydrogen embrittlement were observed at −300 mV, and c) hydrogen embrittlement was obtained at −800 mV and −1000 mV.

Stress corrosion cracking of A517 steel in marine environments

PurposeThe purpose of this study is to develop the existence and mechanism of stress corrosion cracking (SCC) for A517 steel in marine environments.Design/methodology/approachSlow strain rate test (SSRT) and constant load tests were used to investigate the SCC susceptibility of A517 steel. In addition, the additive stresses caused by the corrosion film and hydrogen entering into steel were applied to reveal the fundamental mechanism of the SCC.FindingsThe SCC susceptibility increased due to anodic dissolution and additive stress caused by the corrosion-produced film under anode polarization. Furthermore, the SCC susceptibility increased with increasing cathodic polarization, which is due to the increased additional stress caused by hydrogen entering into the steel. However, when the cathode polarization further increased, the additional stress remained due to the constant hydrogen content, thus the SCC susceptibility did not vary. Moreover, the SCC susceptibility of A517 steel under an alternate immersion environment (AIE) was lower than that under a full immersion environment and the steel under the AIE with 0.5 W/D had the lowest SCC susceptibility.Originality/valueThe stress corrosion behaviors of A517 in marine environments under various conditions were systematically analyzed.