Stress Corrosion Crack Growth Research Articles

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.

Full‐scale testing of near‐neutral pH stress corrosion cracking growth behavior of a vintage X52 oil pipe

AbstractThis study presents an experimental investigation conducted on a 40‐year‐old vintage X52 oil pipe segment to assess the growth behavior of near‐neutral pH stress corrosion cracking (SCC). Six cracks were introduced on the pipe specimen, each of which was associated with a unique combination of metallurgical and environmental condition. SCC growth was evident in two base metal cracks respectively exposed to C2 and NS4. Stress intensity factors at the two cracks were evaluated using extended finite element method. Near‐neutral pH environment effects were observed to have a more pronounced effect on the stress intensity factor threshold for growth than on the growth rate. Higher stress levels and aging likely contribute to the difference in growth rates of different cracks. Electrochemical analysis suggests the corrosion‐crack propagation interplay, with a faster corrosion in the NS4 solution than that in the C2 solution consistent with the observed slower crack growth in NS4.

Mathematical Modeling of Growth of Stress-Corrosion Cracks in an Oil Pipeline with Regard for Hydroshocks and In-Service Changes in the Characteristics of its Material

Mathematical Modeling of Growth of Stress-Corrosion Cracks in an Oil Pipeline with Regard for Hydroshocks and In-Service Changes in the Characteristics of its Material

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.

Electrochemical Evaluation of Al-5 wt% Zn Metal-Rich Primer for Protection of Al-Zn-Mg-Cu Alloy in NaCl

An intact and X-scribed Al-5wt%Zn-rich primer (AlRP) without pretreatment or topcoat was evaluated for its ability to suppress potential-dependent intergranular corrosion and intergranular stress corrosion cracking of peak-aged AA7075A-T651 in NaCl salt fog and full immersion. The ability of the primer to provide sacrificial anode-based cathodic prevention of peak-aged AA7075-T651 substrate was evaluated both under the primer coating and at scratches. The AlRP evaluated consisted an epoxy-based resin embedded with spherical Al-5wt%Zn pigment particles. Performance was evaluated under full immersion in 0.6 M NaCl solution and compared to ASTM B117 salt spray exposure using two approaches. These consisted of the University of Virginia (UVA) cycle test on intact coatings and the full immersion galvanic couple testing on simulated scratched panels created when intact coatings form bimetal couples with bare AA7075-T651. Focus was placed on the ability of the AlRP to achieve a targeted intermediate galvanic couple potential near a “prevention” potential which suppresses stress corrosion crack growth, intermetallic particle corrosion as well as intergranular corrosion. The long-term (24-h) open-circuit potential (OCP) of AlRP-coated AA7075-T651 in 0.6 M NaCl indicated that the AlRP provided less than 100 mV of cathodic potential shift of the intact coating from its OCP in 0.6 M NaCl. Electrochemical cycle testing conducted at a potentiostatic hold of –0.95 VSCE demonstrates that the AlRP did not enable sacrificial anode-based cathodic protection as the coupled potential remained at the corrosion potential of bare AA7075-T651. Furthermore, the current observed throughout galvanic corrosion experiments coupling of AlRP to AA7075-T651 indicated the AlRP coating was a cathode in the bimetal galvanic couple. ASTM B117 salt spray exposure of the AlRP revealed oxidation of the AA7075-T651 substrate below the primer detected as a continually growing oxygen signal at the primer-substrate interface that did not arrest corrosion over the exposure period.

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.

Evaluation of the stress corrosion crack growth behaviour of high-strength marine steel based on model of crack tip mechano-electrochemical effect

Here, the stress corrosion crack growth behaviour of a high-strength low-alloy steel under anodic potential was investigated in artificial seawater. As applied potential shifts positively, the crack growth rate first increases and then decreases. The crack growth behaviour is controlled by the mechano-electrochemical effect at the crack tip. Even under anodic potential, hydrogen embrittlement (HE) occurs at the crack tip, and HE is the main factor of crack growth. A model of mechano-electrochemical effect at the crack tip is developed to study the phenomenon. It was found that applied potentials change the crack growth behaviour via involvement in HE and anodic dissolution at the crack tip. The critical value of applied potential affecting crack growth is the crack tip potential of –0.0591 pH.

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.

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

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

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.

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 thermal aging on the environmental assisted cracking behavior of 308L weld metal in high temperature water

The effect of thermal aging on environmental assisted cracking (EAC) of 308 L weld metal was investigated. Experimental results reveal that thermal aging promotes corrosion fatigue (CF) crack growth with extensive inter-dendritic cracking, but has a limited effect on the stress corrosion cracking (SCC) growth under constant loads. The higher crack tip strain rate and the enhanced preferential oxidation of deteriorated δ-ferrite are responsible for the enhanced CF susceptibility after thermal aging. The dispersed δ-ferrites and the decreased crack tip strain rate account for the high SCC resistance under constant load regardless of the thermal aging.

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.

Pre-cyclic-loading-enhanced Stage-1b stress corrosion crack growth of pipeline steels

The influence of prior cyclic loading on Stage-1b stress corrosion cracking (SCC) growth of X52 pipeline steels was investigated. Results showed that Stage-1b SCC growth was observed for pre-cyclically-loaded specimens under subsequent cyclic loading at the maximum stress intensity factor of 16 MPa m0.5 rather than those without pre-cyclic-loading. Large magnitude of prior stress cycles favored the SCC crack growth and its transition. Intergranular attack by static corrosion contributed marginally to the Stage-1b crack growth. Prior cyclic loading plus heat treatment facilitated strain-aging-assisted SCC crack growth. Removal of the plastically deformed regions before re-coating could reduce the cracking susceptibility.

Overview of Stage 1b Stress Corrosion Crack Initiation and Growth of Pipeline Steels

Stress corrosion cracking (SCC) can cause catastrophic failure of buried pipelines for oil and gas transmission. The life cycle of pipeline steels experiencing SCC consists of five stages: incubation stage, stage 1a (crack initiation), stage 1b (early-stage crack growth), stage 2 (sustainable crack growth caused by mechanical driving force), and stage 3 (rapid crack propagation to rupture). Stage 1b encompasses a large portion of the pipeline’s lifespan, which is of great significance to pipeline integrity management aimed at service life extension. However, this stage is less studied so far. This invited paper provides a brief review of the recent progress on stage 1b stress corrosion crack initiation and growth for buried pipeline steels. Emphasis is placed on the effects of loading conditions and their interactions on stage 1b growth of high pH SCC, while some progress of near-neutral pH SCC is included for the purpose of comparison. It first introduces SCC in pipeline steels which is followed by a definition of stage 1b and its significance in terms of the service life of pipeline steels. Then the most recent advancements in understanding early-stage crack growth in stage 1b are reviewed and discussed. In summary, stage 1b growth can be self-induced by existing cracks (the so-called mother-daughter analogy), involving crack initiation in the plastic zone ahead of the surface tip of a surface crack, which is quite different from the stochastic process of coalescence of randomly formed individual cracks. Stage 1b growth extends crack length and increases the stress intensity factor at the depth tip without a physical increase in crack depth, serving as a bridge to stage 2. Further, the need for future research on stage 1b SCC initiation and growth of pipeline steels is discussed.

Stress and Strain State Analysis of Crack Front in Dissimilar Metal Welded Joints with Dual Field of Mechanical Heterogeneity and Residual Stress

The micro-mechanical state at the crack front is one of the key factors affecting the stress corrosion cracking (SCC) growth behavior. The mechanical heterogeneity and residual stress in the dissimilar metal welded joint (DMWJ) induce the micro-mechanical state at the crack front to become more complex. The sandwich model and dual-field model of the DMWJ with inner surface axial crack were established in this study. The stress and strain states at the crack front with different crack locations and lengths under the interaction of the mechanical property and the residual stress were investigated. The results show that a more accurate evaluation of stress and strain states can be obtained when using the dual-field model to describe the material mechanical property and residual stress of the DMWJ. The sandwich model overestimates the crack driving force including the stress and strain at the crack front. The tensile stress in the middle of shallow cracks is smaller than that at both ends, while the tensile stress in the middle of deep crack is larger than that at both ends. The variation trend of the tensile stress and normal strain at the crack apex is basically the same as that of the residual stress with the crack depth. However, there is almost no normal plastic strain in the initial stage of crack propagation due to the small residual stress in the initial stage.

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.

Tolerance assessment and crack growth of chloride-induced stress corrosion cracking for Chinshan dry storage system

Evaluating the susceptibility of canister used in Chinshan Independent Spent Fuel Storage Installation (CSISFSI) to chloride-induced stress corrosion cracking (CISCC) has been an aging management plan in an initial license period of 20 years. The presence of concentrated chlorides, temperature and relative humidity, and sufficient weld residual stress are the three key environmental conditions for atmospheric CISCC. A single 2-D model was used to simulate natural exposure of austenitic stainless steel (SS) of SS304 and SS304L dry storage system (DSS) for transportable storage canister (TSC). This model will calculate the temperature on the TSC surface based on CFD method. This study estimated RH and DRH on the TSC surface by the realistic environmental conditions (e.g., ambient RH, ambient temperature, and the temperature on the TSC surface) after 1st, 10th, and 20th years, respectively. The flaw tolerance to part-depth (PD) and through-wall (TW) critical flaw were evaluated, and the two-phase CGR induced by CaCl2 or MgCl2 of the TSC surface under 0.18 m height were predicted. The results show that the fastest CISCC CGR was on the bottom induced by CaCl2 in the 20th year, and the slowest CGR was at the 0.18 m of TSC induced by MgCl2 in the 10th year. The two-phase CGR trends were very close if the deliquescence threshold had been considered under different environmental conditions.

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.