Stress Corrosion Cracking Growth Behavior Research Articles

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.

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 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.

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 Cold-Work Degree on Stress Corrosion Cracking Behavior of Alloy 600 in Simulated Boiling Water Reactor (BWR) Water Environments

The growth behavior of stress corrosion cracking (SCC) of Alloy 600 with different cold-work levels was investigated in simulated boiling water reactors water environments. In addition, a correlation of cold-work levels, grain boundary characteristic, and the SCC growth behavior of Alloy 600 were studied. The results show that grains with high residual strain caused by cold work provide transgranular crack growth paths. The SCC growth rates of the specimens also increase with an increase in the degree of cold work and decrease remarkably after switching to the hydrogen water chemistry environment. Grain boundary character proves to be a factor more important than the localized strain concentration at the grain boundary in terms of its role in the intergranular crack growth rate of the Alloy 600 with a cold-work degree from 20% to 30%.

Stress corrosion crack growth rate of welded joint used for low-pressure rotor of nuclear turbine in oxygenated pure water at 180 °C

Stress corrosion cracking (SCC) growth behavior of NiCrMoV steels welded joint of nuclear steam turbine was systematically investigated, which was conducted in pure water with 8 ppm oxygen at 180 °C. Crack growth rate (CGR) was used to evaluate the susceptibility of SCC for WM with fine bainites and HAZ with coarse prior austenite grains, simultaneously the cracking mechanisms for both zones were explored. WM has lower CGR than HAZ under the similar stress intensity factor, showing it had higher resistance to SCC. Oxygen promoted the nucleation and propagation for cracks. The oxygen diffusion zone (ODZ) formed in front of inner oxide layer through continually diffusion of oxygen in grain, and caused the embrittlement and transgranular cracking for WM. However, fine grains in WM could bear crack driving force and reduce stress concentration to increase the resistance for transgranular crack propagation. As for HAZ, the chromium-rich carbides along the prior austenite grain boundaries (PAGBs) accelerated the intergranular oxidation and facilitated the formation of intergranular oxide zone (IOZ). Thus, the crack could easily propagate in PAGB, and lead to higher CGR for the HAZ.

Comparison of the stress corrosion cracking growth behavior of cold worked Alloy 690 in subcritical and supercritical water

The stress corrosion cracking growth behavior of cold worked Alloy 690 has been studied in high temperature pressurized water at temperatures between 360 °C and 550 °C. Creep induced cracking was measured at each testing temperature in inert argon environment. Experimental results showed that creep contributed to more than 80% of the overall crack growth rate at temperatures above 450 °C, while only 8% at 360 °C. Sensitization of the post-tested specimens was quantitatively identified, which increased with the testing temperature. The increased degree of sensitization may also contribute to a portion in the overall crack growth rate. It was clearly proved that the dominant mode of cracking from subcritical to supercritical temperatures are different for cold worked Alloy 690. Corrosion induced cracking controls the crack growth rate in subcritical water environment, while creep is the major factor that dominates the cracking in supercritical water.

Investigation on machining induced surface and subsurface modifications on the stress corrosion crack growth behaviour of super duplex stainless steel

After stress corrosion crack testing in a MgCl2 environment, turned surface of super duplex stainless steel showed four types of cracks. The residual stress and surface defects such as feed marks and long grooves generated after machining played a significant role in the direction and orientation of these cracks. The generated cluster of cracks acted as a precursor to the formation of pits. The biaxial tensile stress in the surface promoted successive branching of cracks, which led to high crack density. The subsurface results showed that cracks passing perpendicular to feed marks found more detrimental than the other types.

Stress Corrosion Crack Growth Behavior of Type 310S Stainless Steel in Supercritical Water

Stress corrosion crack (SCC) behavior of Type 310S stainless steel (SS) in supercritical water was evaluated at 400°C to 550°C. Crack growth rates (CGR) were obtained as a function of temperature and corrosion potential. Results show that Type 310S SS exhibits 100% intergranular SCC, and creep plays an important role in the overall growth rate. The SCC CGR increases with temperature between 400°C and 550°C, and is higher at a medium-low corrosion potential (argon deaerated water) than in water with dissolved O2 or dissolved H2. A mechanism for SCC of Type 310S SS in supercritical water is proposed to explain the combined effect of SCC and creep.

On the stress corrosion crack growth behaviour in high temperature water of 316L stainless steel made by laser powder bed fusion additive manufacturing

This paper reports a comprehensive study of the stress corrosion crack growth behaviour of laser additively-manufactured (AM) 316L stainless steel in high temperature water. A wide range of parameters and their effects were evaluated, including microstructure, heat treatment, stress intensity factor, cold work, crack orientation, oxidizing vs. reducing conditions, and porosity. Stress-relieved material exhibits anisotropic microstructure and preferred crack path along material’s build direction. With high-temperature annealing, the material recrystallizes to equiaxed structure and behaves like wrought material. The retained unrecrystallized grains in an annealed AM part may not affect the cracking. Increased porosity may enhance the crack growth rate.

Effect of Local Strain Distribution of Cold-Rolled Alloy 690 on Primary Water Stress Corrosion Crack Growth Behavior

Abstract This work aims to study the stress corrosion crack growth behavior of cold-rolled Alloy 690 in the primary water of a pressurized water reactor. Compared with Alloy 600, which shows typical intergranular cracking along high angle grain boundaries, the cold-rolled Alloy 690, with its heterogeneous microstructure, revealed an abnormal crack growth behavior in mixed mode, that is, in transgranular cracking near a banded region, and in intergranular cracking in a matrix region. From local strain distribution analysis based on local mis-orientation, measured along the crack path using the electron back scattered diffraction method, it was suggested that the abnormal behavior was attributable to a heterogeneity of local strain distribution. In the cold-rolled Alloy 690, the stress corrosion crack grew through a highly strained area formed by a prior cold-rolling process in a direction perpendicular to the maximum principal stress applied during a subsequent stress corrosion cracking test.

Bayesian nonparametric analysis of crack growth rates in irradiated austenitic stainless steels in simulated BWR environments

To investigate influential parameters for irradiation-assisted stress corrosion cracking (IASCC) growth behavior, we attempt to analyze statistically existing data on the crack growth rate (CGR) in irradiated austenitic stainless steels (SSs) in boiling water reactor (BWR) environments using the Bayesian nonparametric (BNP) method. From the probability distribution of CGR and some input parameters, such as yield stress of irradiated material (σYS-irr), stress intensity factor (K), electrochemical corrosion potential (ECP), and fast neutron fluence, the mean CGR is estimated and compared with the measured CGR. The analytical results show good reproducibility of the measured CGR. The results also indicate the possible neutron fluence effects on CGR in high CGR region (i.e., high neutron fluence condition) by radiation-induced segregation (RIS), localized deformation, and/or other mechanisms than radiation hardening.

The influence of ppb levels of chloride impurities on the stress corrosion crack growth behaviour of low-alloy steels under simulated boiling water reactor conditions

The effect of chloride on the stress corrosion crack (SCC) growth behaviour in low-alloy reactor pressure vessel steels was evaluated under simulated boiling water reactor conditions. In normal water chemistry environment, ppb-levels of chloride may result in fast SCC after rather short incubation periods of few hours. After moderate and short-term chloride transients, the SCC crack growth rates return to the same very low high-purity water values within few 100h. Potential long-term (memory) effects on SCC crack growth cannot be excluded after severe and prolonged chloride transients. The chloride tolerance for SCC in hydrogen water chemistry environment is much higher.

Effect of Local Strain Distribution on Stress Corrosion Cracking of Cold-Rolled Alloy 690 With Inhomogeneous Microstructure

This article undertakes an investigation of the stress corrosion crack growth behavior of a cold-rolled Alloy 690 (UNS N06690) with microstructural inhomogeneity in the primary water of a pressurized water reactor, and ascertains the relationship between this behavior and the local distribution of the residual strain. Stress corrosion cracking (SCC) was found to propagate in a transgranular mode through a banded region composed of intragranular carbides and small-sized grains, and in an inter-granular mode through a normal matrix region of normal-sized grains, with an abnormally high growth rate when aligning the cold-rolling and crack growth directions with the intragranular carbide bands. The Vickers hardness and the degree of misorientation increased as plastic deformation as a result of cold-rolling proceeded. Moreover, these parameters were consistently higher in the banded region than in the matrix region. From an analysis of the residual strain, it was suggested that higher residual strain near int...

Estimation of Stress Corrosion Cracking Growth Behavior Under Weld Residual Stress in the Bottom of a Reactor Pressure Vessel by Finite Element Analysis

A method for evaluating crack growth by repeatedly modeling and analyzing the transitional crack shapes is developed for a general computing environment in which a commercial finite element preprocessor and analysis code are used. The proposed method calculates stress intensity factors (SIFs) by finite element analysis (FEA) by directly distributing estimated weld residual stress obtained from noncracked components on the crack surface on the basis of the superposition principle. In present case, to specify a nonuniform residual stress distribution, a subroutine for a commercial FEA code (ABAQUS) was developed. Arbitrary crack shapes during the crack propagation were expressed by applying the submodeling technique which allowed arbitrary crack shapes to be meshed. The sequence of steps in the proposed method was designed to make it possible to consider complicated stress distributions, such as weld residual stress, and to express arbitrary crack shapes. The applicability of the proposed FEA based method was verified by comparing the result of a stress corrosion cracking (SCC) growth analysis results of a flat plate obtained with the proposed method and with the ASME code procedure. As an application example, the SCC growth behavior of a crack at the bottom of a nuclear reactor pressure vessel (RPV) involving a dissimilar metal weld and a unique geometry was evaluated by the proposed method. The evaluation results were compared with results obtained using a conventional method, i.e., the influence function method (IFM). Since both sets of results were in reasonable agreement, it was concluded that IFM can be applied to this case. Previously, it was difficult to assess the applicability of conventional methods, such as the code procedure and IFM, to a complicated problem because of the existence of complicated residual stress fields, dissimilar metals, and the complicated crack shapes involved. The proposed method using FEA allows the applicability of conventional methods to complicated crack growth evaluations to be assessed.

PS0016-258 ステンレス鋼のSCCき裂進展挙動に及ぼす荷重条件の影響

PS0016-258 ステンレス鋼のSCCき裂進展挙動に及ぼす荷重条件の影響

Intergranular Stress Corrosion Cracking Growth Behavior of Ni-Cr-Fe Alloys in Pressurized Water Reactor Primary Water

The purpose of this research was to compare the stress corrosion cracking (SCC) resistance of materials used at the present time for steam generator (SG) tubing in pressurized water reactor (PWR) primary water. Our results in PWR primary water for 20% cold-worked (CW) Alloy 800 (UNS N08800) are compared with already published data for SCC growth from 20%CW Alloy thermally treated (TT)690 (UNS N06690), 20%CW Alloy mill-annealed (MA)600 (UNS N06600), and 20%CW austenitic stainless steels. The second purpose was to examine the dependence of SCC growth on nickel and chromium in PWR primary water; the objective was to obtain the basic knowledge to understand SCC behavior of SG tubing materials. The third objective was to understand whether accelerated testing at higher temperatures is appropriate for predicting SCC initiation and growth at lower temperatures. For these objectives, SCC growth was measured in PWR primary water at 290, 320, 330, 340, and 360°C under static load conditions. Tests were performed us...

Stress corrosion cracking in dissimilar metal welds with 304L stainless steel and Alloy 82 in high temperature water

For a better understanding toward stress corrosion cracking (SCC) in dissimilar metal welds with 304L stainless steel and Alloy 82, the SCC growth behavior in the transition regions of weld joints was investigated via slow strain rate tensile (SSRT) tests in 280 °C pure water with a dissolve oxygen level of 300 ppb. Prior to the SSRT tests, samples with dissimilar metal welds were prepared and underwent various pretreatments, including post-weld heat treatment (PWHT), shot peening, solution annealing, and mechanical grinding. In addition to the SSRT tests, measurements of degree of sensitization and micro-hardness on the transition regions of the metal welds were also conducted. According to the test results, the samples having undergone PWHTs exhibited relatively high degrees of sensitization. Distinct decreases in hardness were observed in the heat-affected zones of the base metals in all samples. Furthermore, the fracture planes of all samples after the SSRT tests were located at the stainless steel sides and were in parallel with the fusion lines. Among the treating conditions investigated in this study, a PWHT would pose a detrimental effect on the samples in the aspects of mechanical property and degree of SCC. Solution annealing would lead to the greatest improvement in ductility and SCC retardation, and shot peening would provide the treated samples with a positive improvement in ductility and corrosion retardation, but not to a great extent.

Effect of Welding Conditions on Residual Stress and Stress Corrosion Cracking Behavior at Butt-Welding Joints of Stainless Steel Pipes

Stress corrosion cracking (SCC) in Type 316 L low-carbon austenitic stainless steel recirculation pipes have been observed near butt-welding joints. These SCC in Type 316 L stainless steel grow near the welding zone mainly because of the high tensile residual stress caused by welding. Therefore, for SCC growth analysis, it is important to assess the residual stress caused by welding of stainless steel piping. In the present study, which is focused on the scatters of welding parameters such as heat input and welding speed, these values were measured experimentally by fabricating a series of butt-welded specimens of Type 316 pipes. The distribution and scatter of residual stress were also measured by stress relief and X-ray diffraction methods. The effects of welding parameters on residual stress distribution have been evaluated through welding simulations based on finite-element analysis using three-dimensional and axisymmetric models. Parametric analyses were also performed, while taking into account the variation of some welding parameters based on the experiments. SCC growth behavior was calculated using simulated residual stress distributions and applying a procedure in the fitness-for-service code. It was clearly shown that the uncertainties on welding heat input and speed have strong influences on SCC growth behavior because residual stress is also affected by the scatter of these welding parameters.