Stress Corrosion Crack Growth Rate Research Articles

Analysis of Stress Corrosion Cracking Growth Rate in the Heat-Affected Zone of 316L Based on the Heterogeneity of the Mechanical Properties

The heterogeneity of the microstructure and mechanical properties of safe-end dissimilar metal welded joints (DMWJs) presents a challenge to the quantitative prediction of the stress corrosion cracking (SCC) growth rate directly from laboratory data. This study investigates the effect of the heterogeneity of the mechanical properties of the 316L-welded heat-affected zone (HAZ) in safe-end DWMJs on the SCC tip stress-strain field and the SCC growth rate. First, based on the analysis of microstructures in localized regions within the 316L-welded HAZ and the acquisition of material mechanical properties through microhardness testing, a user-defined material subroutine was developed to characterize the heterogeneous material properties within the 316L-welded HAZ. Then, using this finite element model with an inhomogeneous distribution of the mechanical properties of the material, the crack tip strain rates (CTSRs) at different locations within the 316L-welded HAZ were obtained. In conjunction with the FRI model, the SCC growth rates at various locations within the HAZ were determined. The results show that the closer to the 52Mw/316L fusion boundary within the 316L-welded HAZ, the greater the yield strength of the material and the higher the CTSR and predicted SCC growth rates at the characteristic distance.

Machine Learning-Assisted Prediction of Stress Corrosion Crack Growth Rate in Stainless Steel

Stainless-steel is extensively utilized in the key structural components of the main equipment in the nuclear island of pressurized water reactor nuclear power plants. The operational experience of nuclear power plants demonstrates that stress corrosion is one of the significant factors influencing the long-term safe operation of stainless steel in the high-temperature water of pressurized water reactor nuclear power plants. This study is based on the stress corrosion crack growth rate data of 316SS and 304SS stainless steel in the simulated primary water environment of pressurized water reactor nuclear power plants. Data mining and modeling were conducted using multiple machine learning algorithms, including Random Forest (RF), eXtreme Gradient Boosting (XGBoost), Support Vector Regression (SVR), and Gaussian Process Regression (GPR), and the Sharpley Additive explanation (SHAP) method was employed to analyze the interpretability of the model. The results indicate that the stress corrosion crack growth rate prediction model based on XGBoost outperforms other models in all assessment indicators. Compared with empirical equations, XGBoost exhibits high flexibility and excellent data-driven learning capabilities. In the test set, 90% of the prediction errors are within the range of experimental values, with the maximum error multiple being 2.5, which significantly improves the prediction accuracy. Moreover, the distribution of SHAP values is consistent with the theoretical study of the stress corrosion behavior of stainless-steel, effectively reflecting the impact of cold working, temperature, and stress intensity factor on the stress corrosion crack growth rate, thereby proving the reliability of the model’s prediction results. The achievements of this study hold significant reference value and application prospects for the prediction of the stress corrosion behavior of stainless-steel in a high-temperature and high-pressure water environment of pressurized water reactor nuclear power plants.

Prediction of dK/da effects on stress corrosion crack growth rate of irradiated stainless steels based on slip oxidation mechanism

This study developed a predicting method for the crack growth rate (CGR) of stress corrosion cracking (SCC) under varying stress intensity factor (K) conditions for irradiated stainless steel (SS). First, optimization of the Hashimoto-Koshiishi model equation for calculating CGR under varying dK/da conditions was carried out using the Rice, Dugan, and Sham (RDS) equation for the crack tip strain rate. Second, the model input coefficients were set to incorporate the effect of dK/da on SCC CGR to fit the experimental data. Finally, the effect of dK/da on the CGR for 3 dpa irradiated SS of a core shroud was evaluated taking into account the weld residual stress distribution. The model prediction showed that there was little effect on the CGR for the increasing and decreasing K regions in the plate thickness direction of the core shroud under boiling water reactor (BWR) normal water chemistry, but the effect was not negligible for the decreasing K region under BWR hydrogen water chemistry.

Effect of cold work level on the crack propagation behaviour of 316LN stainless steel in high-temperature pressurized water

We investigated the microstructure, mechanical properties, and stress corrosion cracking (SCC) propagation behaviour of 316LN austenitic stainless steel with various cold work (CW) levels. CW increased the crack growth rate of 316LN. The stress corrosion crack growth rate (SCCGR) for 316LN with 5% CW was approximately 6.52% higher than that of the solution-annealed state; 10%, 20%, and 30% CW resulted in 1.20, 3.18, and 6.10 times higher SCCGRs, respectively. A larger residual strain and proliferation of slip bands via cold deformation augmented the SCCGR. The SCC propagation mechanism of 316LN changed with increasing CW levels owing to slip bands.

Ameliorating dilution of Cr and Ni and improving PWSCC resistance of 52 M overlay by hot wire plasma arc cladding

The multi-scale chemical composition distribution and microstructure of Alloy 52 M overlay on low alloy steel by hot wire plasma arc cladding (HWPC) were characterized. Stress corrosion cracking (SCC) growth rates were quantified in the dilution zone (DZ) near the fusion boundary and in the bulk of Alloy 52 M using compact tension samples with a thickened cladding overlay. The DZ of the Alloy 52 M side exhibited a single macroscopic dilution zone containing approximately 27–28 wt% Cr and 50 wt% Ni, in contrast to the multiple dilution zones observed in the DZ of Alloy 52 M overlays or joints prepared using other welding technologies such as submerged arc welding (SMAW). The DZ of the HWPC overlay exhibited less dilution of Cr and Ni compared to SMAW weldment. This resulted in a shorter average SCC band and fewer local intergranular cracks in the DZ of HWPC, as observed from SCC crack growth rate specimens tested in simulated PWR primary water at 325 °C and 350 °C. These findings highlight the advantages of utilizing HWPC to enhance SCC resistance in the DZ of Alloy 52 M overlays over conventional cladding technologies.

Prediction of stress corrosion crack growth rate of cold worked stainless steels in BWR conditions by the slip oxidation model

Stress corrosion cracking (SCC) is a critical issue for boiling water reactor (BWR) components, and their cold working is considered to be an accelerating factor for SCC crack growth rates (CGRs). However, no method has been proposed to quantitatively evaluate the SCC CGRs of cold worked stainless steels. In this study, the changes in material properties due to cold working were reflected in the input parameters of the Hashimoto-Koshiishi model, a mechanistic model of SCC growth based on the slip oxidation mechanism, to enable a quantitative evaluation of the SCC crack growth rate (CGR) of cold worked SSs. In addition, a simplified equation as a function of the yield strength of cold worked 316LSSs was developed for ease of practical use in the integrity assessment of components. The CGRs calculated by the model and/or the simplified equation were in good agreement with the experimentally obtained CGRs for cold worked SSs and the heat affected zone (HAZ) of Type 316L SSs.

Effect of material chemical composition on oxidation and stress corrosion cracking of the submerged arc welding Alloy 52M overlay in a simulated PWR primary water

Compact tension (CT) specimens from submerged arc welding Alloy 52 M overlay are used to determine the stress corrosion cracking (SCC) resistance of the dilution zones and bulk overlay metal on the 52 M side in a simulated pressurized water reactor (PWR) primary water. SEM-EDS and X-ray fluorescence spectroscopy (XRF) results show three dilution zones (DZs) on the 52 M side. Oxidation test results show that the thickness of the compact oxide layer and maximum local oxidation penetration depth decrease for 1st DZ, 2nd DZ, and bulk 52 M, which are consistent with the average SCC growth rate and the number of local intergranular SCC cracks in these regions. The dilution zones with low Cr but high Fe content possess lower oxidation and SCC resistance than the bulk 52 M.

Prediction of stress corrosion crack growth rate of irradiated alloy X-750 with different crack tip strain rate models

This study developed a prediction method for the crack growth rates (CGRs) of irradiated X-750 using the crack tip strain rate. First, the optimum input parameters for the Hashimoto-Koshiishi model, which is a mechanistic crack growth model of stress corrosion cracking (SCC), were obtained for unirradiated X-750. Second, the methodology to incorporate the effect of neutron irradiation on SCC CGRs was developed to fit the experimental data. The strain rate equation for elastic-ideally plastic materials was employed for evaluating the crack tip strain rate since irradiated X-750 showed no strain hardening in its stress–strain curve. Calculated CGRs agreed well with experimental CGRs at 0.3 dpa and 1.4 dpa not only for normal water chemistry but also for hydrogen water chemistry. Finally, the CGR dependency on irradiation dose was evaluated with the developed model. The model prediction showed that the CGRs increased slowly with irradiation dose and became almost constant above 1 dpa.

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.

Оценка скорости развития трещин и ресурса магистральных трубопроводов

In this article, based on determining strain parameters such as the equivalent (von Mises) strain and average strain, calculations of the depth growth rate of fatigue and stress-corrosion cracks as well as the operating life of the pipeline sections are performed. The results are presented as the operating time to failure and cycles number to failure by loading internal pressure. The obtained graphs of the dependence of the crack growth rate, crack depth, equivalent (von Mises) strain, average strain in the defective zone on the pipeline operation time are presented. During computational experiments for the main pipeline the destructive depth of defects, the residual operating life of the pipeline with cracks having different initial depth and length were determined.

Probabilistic analysis of crack tip mechanical properties in welded joints for nuclear structures

The crack tip mechanical properties of welded joints are essential factors that influence the failure and stress corrosion cracking (SCC) behaviors of nuclear structures. Owing to the inherent statistical characteristics of the load, material properties, and geometric parameters, the mechanical properties of the crack tips of the base and weld metals in welded joints are uncertain and inhomogeneous. Because welded joints are prone to failure and SCC, a probabilistic methodology for determining the crack tip mechanical properties based on the elastic–plastic finite element and sparse polynomial chaos expansion methods was developed to investigate the influence of material mismatch and uncertainties in welded joints on the failure probability and SCC growth rate. To process the results more efficiently, MATLAB was used for pre- and post-processing during the automated simulation procedure using ABAQUS finite element software. The mechanical properties of the welded joints, such as their J-integrals and plastic strain zones, were examined. Additionally, the failure probabilities and SCC growth rates were determined based on the statistical characteristics of the mechanical properties of the welded joint. The material mismatch and uncertainties in a welded joint have a significant influence on the probabilistic distribution of the mechanical properties of the crack tip, thereby influencing its failure probability and SCC growth rate.

Effect of Material Inhomogeneity on the Crack Tip Mechanical Field and SCC Growth Rate of 52M/316L Dissimilar Metal Welded Joints

The stress–strain conditions at the crack tip in dissimilar metal welded joints (DMWJ) are a critical factor influencing stress corrosion cracking (SCC) behavior. The processing technology and working environment of DMWJ lead to a randomly inhomogeneous distribution of material mechanical properties, making the crack tip mechanical field more complex. An inhomogeneous model was obtained using a combination of physical experiments and the elastic–plastic finite element method to understand the effect of this inhomogeneous distribution of mechanical properties on the direction of SCC growth and the growth rate in DMWJ and the impact of inhomogeneity on the SCC growth behavior was compared and analyzed. The findings demonstrate that Type I (opening mode) cracks are more likely to form due to the inhomogeneity of mechanical properties and are more likely to deflect toward the Alloy 52M region at the interface between Alloy 52M and 316L stainless steel. Additionally, the strain gradient at the crack tip increases with the degree of inhomogeneity, which has a bigger impact on the accuracy of SCC growth rate predictions.

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.

Formulation of Irradiation Assisted Stress Corrosion Crack Growth Rates for Neutron-Irradiated Stainless Steels under Hydrogen Water Chemistry Conditions of Boiling Water Reactors

ABSTRACT This study developed a formula for the calculation of crack growth rates (CGRs) of irradiated austenitic stainless steels (SSs) under hydrogen water chemistry (HWC) conditions of boiling water reactors. First, the input parameters for the Hashimoto–Koshiishi model, which is a mechanistic crack growth model of stress corrosion cracking (SCC), were optimised for SSs irradiated up to 11 dpa. Electrochemical corrosion potential (ECP) of those SSs during crack growth tests nearly equalled −200 mVSHE. Second, a simplified formulation was developed to reproduce the model calculations of SSs. Calculated CGRs agreed well with experimental CGRs of various types of SSs, which were irradiated up to 13 dpa and tested at ECPs from −550 mVSHE to −200 mVSHE, when the experimental CGRs were less than the values for NWC conditions. On the other hand, there were some data in which experimental CGRs were much higher than calculated CGRs. By analysis of the experimental conditions of the data, the possible influencing factor for the discrepancy between the calculated and experimental CGRs was found to be the -validity. If the -validity criterion was not satisfied, the strain distribution used in the model calculation was not adequate for the actual strain distribution.

Impact of Chloride on the Environmentally-Assisted Crack Initiation Behaviour of Low-Alloy Steel under Boiling Water Reactor Conditions

Low-alloy reactor pressure vessel steels have a rather low susceptibility to stress corrosion cracking (SCC) in a boiling water reactor (BWR) environment if the high-temperature water contains no anionic impurities. Recent investigations revealed that under oxidizing BWR normal water chemistry (NWC) conditions extremely small amounts of chloride, can cause very high SCC growth rates in these materials. Therefore, the effect of continuous and temporary chloride additions on the crack initiation behaviour was explored by a series of constant extension rate tensile (CERT) and constant load tests in high-temperature water. In an NWC environment, containing ≥2 ppb of chloride, strain-induced corrosion cracking (SICC) initiation occurred briefly after the onset of plastic yielding and at much smaller strains than in high-purity water. On the other hand, under reducing hydrogen water chemistry conditions with up to 700 ppb chloride, no SICC was detected up to very high strains. CERT experiments, with moderate short-term chloride transients before and during the loading, showed that even serious mechanical loading transients, one day after returning to high-purity water, did not result in early SICC initiation.

Correlating oxidation resistance to stress corrosion cracking of 309L and 308L stainless steel claddings in simulated PWR primary water

Stress corrosion cracking (SCC) growth behaviors of 309L and 308L stainless steel claddings in simulated pressurized water reactor primary water at 325 °C and 350 °C were investigated by compact tension specimens and correlated to the oxide film properties in terms of microstructure. SCC growth rates of 308L were much lower than those of 309L. 309L showed typical intergranular SCC characteristics. The high SCC resistance of 308L was related to the low oxidation rate and crack tip retardation due to the presence of highly networked ferrites. The lower Cr content, as well as less and sparsely distributed δ-ferrite phases in 309L than in 308L, led to more severe local oxidation penetration beneath the metal/inner oxide interface and more porous inner oxide, therefore, contributed to its enhanced SCC growth in 309L. The SCC growth rate results by compact tension specimens are consistent with those by slow strain rate tests.

Reflections on Early Stages of Environmentally Assisted Cracking from Corrosion Pits

A perspective is presented on the evolution of damage due to environmentally assisted cracking (EAC), from crack precursor development through to long crack growth. The variable nature of crack precursors is highlighted with an observation that uncontrolled chemistry excursions or fabrication defects could eliminate any significant delay associated with that step in the damage evolution process. Specimen preparation by machining and grinding can be critical in determining the apparent susceptibility of the metal to EAC and corrosion, and an example for 316L stainless steel is given to show how physical defects generated by the grinding wheel can become the dominant site for pitting attack relative to MnS inclusions. Corrosion pits are the most commonly observed precursor to cracks in aqueous chloride environments. The loci of sites of crack initiation around a pit are discussed and the inherent challenges in quantifying the growth of cracks smaller than the pit depth described with implications for modelling of the pit-to-crack transition. The remarkably enhanced stress corrosion crack growth rate data for short and small cracks in a 12Cr steam turbine blade in a simulated condensate environment are discussed in the context of crack electrochemistry modelling and the implications for engineering integrity.

Effect of Cold Working and Long-Term Heating in Air on the Stress Corrosion Cracking Growth Rate in Commercial TT Alloy 690 Exposed to Simulated PWR Primary Water

The authors have previously reported that the number of cavities at or near grain boundary (GB) carbides in commercial thermally treated (TT) Alloy 690 increases with increasing cold work reduction ratio and with heating temperature in air. In the present work after very long-term heating in air, the number of cavities at or near GB carbides in cold worked commercial TT Alloy 690 was observed to saturate, and the shape and size of the cavities changed. The shape and size of cavities and cracks were categorized, and a GB defect index number was defined as a function of their number, shape and size. Stress corrosion cracking growth rates in a commercial TT Alloy 690 with various levels of cold work exposed to simulated PWR primary water at 633 K (360 °C) have been measured and correlated with the defined GB defect index number. Cavities and cracks in the same materials before and after long-term heating in air have also been correlated with the defined GB defect index number. For the heavily cold worked (≥ 15 pct) commercial TT Alloy 690, a good correlation has been observed between the PWSCCGR and the GB defect index number. By contrast, for lightly cold worked (≤ 10 pct) commercial TT Alloy 690, the SCCGR in the simulated PWR primary water was very low and the GB defect index number was usually zero, regardless of cold working reduction ratio ≤ 10 pct. It is concluded that the mechanism of SCCGR for lightly cold worked TT Alloy 690 in PWR primary water is likely to be different from that for heavily cold worked TT Alloy 690.

Atmospheric stress corrosion crack growth rates of 316 L stainless steel for nuclear waste containment

Atmospheric stress corrosion cracking (SCC) tests were conducted for a 316 L stainless steel (SS) at an applied stress of 1.1 σ0.2 with a chloride deposition density of approximately 100 μg/cm2 deposited as MgCl2 from solution. The test specimens were exposed in an atmospheric chamber at a constant temperature of 40 °C with initial relative humidity (RH) of 40 %, followed by an increase to 60 % RH, then 80 % RH, and finally a decrease to 60 % RH. The total exposure period was 6500 h (about 9 months). The stress corrosion crack growth rate decreased with increasing RH and with increasing crack depth.

Technical Basis Part 2 for Code Case N-889: Reference Stress Corrosion Crack Growth Rate Curves for Irradiated Austenitic Stainless Steels in Light Water Reactor Environments

Abstract A multiyear international data collection, data review, modeling, and implementation project was recently completed, producing stress corrosion crack growth rate (CGR) reference curves for irradiated austenitic stainless steels in light water reactor (LWR) environments that were adopted as ASME B&PV Section XI Code Case N-889. As described in a technical basis Part 1 paper, over 800 CGR data points were collected from six laboratories worldwide, an international expert panel reviewed and ranked the data, and the better-ranked data were used to calibrate empirical models for irradiation-assisted stress corrosion cracking (IASCC) CGR in boiling water reactor (BWR) normal water chemistry (NWC), BWR hydrogen water chemistry (HWC) and pressurized water reactor (PWR) primary water environments. Part 1 also describes the custom fitting process, quality of fit, and comparisons with related literature and data not used for fitting. This technical basis Part 2 paper describes shifting the mean models to the 75th percentile of the calibration data, simplifying to produce the N-889 curves, and comparing with previous reference curves and over 500 data points not used for developing the N-889 curves, including weld, cast, and heat-affected-zone (HAZ) materials, additional wrought laboratory data, and field data from repeated inspection of BWR core shrouds. Part 2 also describes the irradiated yield stress model in Case N-889, compares that model with its calibration data and other data not used for calibration, and presents example calculations using both yield stress and CGR equations.