Stress Corrosion Cracking Crack Growth Rate Research Articles

Influences of microstructures and macrozones on the stress corrosion cracking sensitivity of a near alpha titanium alloy

In this study, we investigated stress corrosion cracking (SCC) behaviors in a near alpha titanium alloy (Ti-6Al-3Nb-2Zr-1Mo) with distinct microstructures and microtextures. By analyzing fracture surfaces, crack growth paths, and grain orientations, we found that the SCC crack growth rate increased with an increase in the volume fraction of the primary αp phase, due to elevated crack initiation density and concentrated grain orientations. Additionally, SCC cracks exhibited a preference for propagating along boundaries between neighboring soft macrozones (easy for slip) and hard macrozones (relatively hard for slip), as well as through macrozones favorable for slip.

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 Anodic Polarization on the Susceptibility of AA6111 Automotive Sheet to Stress Corrosion Cracking

AA6xxx Al-Mg-Si-Cu alloys are increasingly used to meet lightweight objectives in automotive applications given their high strength-to-weight ratio. However, their use in conjunction with steels and carbon fiber-reinforced polymers in these applications will result in galvanic coupling that may be deleterious to the Al alloy. As such, the ability of anodic polarization to induce stress corrosion cracking (SCC) in AA6xxx, an alloy typically considered SCC-resistant, is explored. In this study, fracture mechanics-based testing under full immersion in 0.6 M NaCl was used to quantify the threshold stress intensity above which SCC can occur (KTH) and stage II SCC crack growth rate (da/dtII) as a function of applied potential at and above the freely corroding potential. Under freely corroding conditions and potentials applied within the range observed for the freely corroding potential, no SCC was observed as results matched those gathered in the air (i.e., KTH was equivalent to the measured fracture toughness). When applying potentials anodic to the freely corroding potential (greater than −706 mVSCE), a decrease in KTH and an increase in da/dtII was observed. Crack growth rates measured under anodic polarizations were slowed through the reapplication of the freely corroding potential. These data imply that galvanic coupling may have the capacity to induce severe SCC in AA6111.

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.

An Investigation of a New Parameter Based on the Plastic Strain Gradient to Characterize Composite Constraint around the Crack Front at a Low Temperature.

Stress corrosion cracking (SCC) is an important destruction form of materials such as stainless steel, nickel-based alloy and their welded components in nuclear reactor pressure vessels and pipes. The existing popular quantitative prediction models of SCC crack growth rate are mainly influenced by fracture toughness values KJc or Jc. In particular, the composite constraint, containing the in-plane constraints and out-of-plane constraints around the crack front, has a significant influence on the fracture toughness of structures in nuclear power plants. Since the plastic strain gradient is a characterization parameter of the quantitative prediction model for crack growth rate, it may be a characterization parameter of composite constraint. On the basis of the experimental data at a low temperature of alloy steel 22NiMoCr3-7 used in nuclear pressure vessels, the gradient of equivalent plastic strain DPEEQ around the crack fronts at different constraint levels was calculated using the finite element method, which introduces a new non-dimensional constraint parameter Dp, to uniformly characterize the in-plane and out-of-plane constraint effects. Compared with constraint parameters APEEQ or Ap, the process of obtaining parameters DPEEQ or Dp is much simpler and easier. In a wide range, a single correlation curve was drawn between parameter Dp and normalized fracture toughness values KJc/Kref or Jc/Jref of specimens at a low or high constraint level. Therefore, regardless of whether the constraint levels of the structures or standard specimens are low or high, constraint parameter Dp can be used to measure their fracture toughness. To build an evaluation method that has structural integrity and safety while containing the composite constraint effects, in addition to accurate theoretical interpretation, further verification experiments, numerical simulations and detailed discussions are still needed.

Stress corrosion crack propagation affected by microstructures for nuclear steam turbine rotor steels in the simulated environment

The propagation behavior of stress corrosion cracking (SCC) for two CrNiMoV steels in the simulated environment of low-pressure nuclear steam turbine rotor was systematically investigated by microstructural characterizations, electrochemical measurements, slow strain rate tensile tests, and crack growth rate (CGR) measurements. The results showed that both the corrosion susceptibility and stress corrosion susceptibility increased with the increase of localized residual strain, yield strength, and the decrease of grain size. With the higher stress corrosion susceptibility, the SCC CGR of Steel A was higher than Steel B in the corrosive solution at 80 °C, however, at 180 °C the SCC CGR of Steel A was lower than Steel B under the lower applied K. The change of SCC CGR was strongly affected by crack branches, crack deflections and plastic deformation during the SCC propagation, which may have some correlations with the microstructural distribution.

Crack Propagation in Pipelines Under Extreme Conditions of Near-Neutral PH SCC

Stress Corrosion Cracking (SCC) process through which cracks occur in a variety of susceptible materials is a result of a combination of residual or applied stresses and corrosion. In oil and gas field, buried pipeline steels are made of low-alloy steels with a ferritic-pearlitic structure, such as X70. In dilute solutions, these materials are prone to SCC failure. The Near-neutral simulated soil solution (NS4) solution is established to imitate SCC conditions and subsequently became the industry requirement for crack growth experiments in the majority of laboratories. The strain-assisted active crack pathways are considered while modelling SCC growth as an oxide film rupture and anodic dissolution process. It’s been hypothesized that increasing the strain concentration can help with dissolution at the film-free crack tip. This research focuses on estimating the SCC crack growth rate under various environmental conditions in oil and gas pipelines using finite element modelling. The simulation is carried out using the J-integral theory in the COMSOL Multiphysics program. Simulations are performed to model the crack growth rate (CGR) using slip anodic dissolution (film rupture) mechanism. The plastic strain gradient is required to compute the SCC CGR (da/dt). Because the plastic strain located at crack tip increases proportionally to the crack length as it propagates, the CGR increases as the stress intensity factor (SIF) increases. The crack growth rates increase when constant loads are applied and as the temperature rises, and elevating the cathodic potential has a minimal influence on the propagation rate of cracks but raises the material yield strength and imparts brittle behavior to it.

Effect of XFEM mesh density (mesh size) on stress intensity factors (K), strain gradient ([formula omitted]) and stress corrosion cracking (SCC) growth rate

The extended finite element method (XFEM) is now widely used for crack simulations. The researchers have performed the crack simulations using the XFEM without re-meshing. Due to recent problems of discrepancies in the experimental and computational results, the mesh density (numbers of elements/unit area) or mesh size of the XFEM is a questionable field. In this research, the effect of the XFEM mesh density (mesh size) on stress intensity factors (K), strain gradient (dεdr) and stress corrosion cracking (SCC) growth rate has been investigated using the XFEM method provided by the ABAQUS. Two specimens with embedded cracks in a flat plate of Inconel-600, under the same load and environment (340 °C), are used. The embedded cracks are of different lengths with localized circles of randomly chosen radius. The stress intensity factors, K, strain gradient with respect to the propagated crack, dεdr, and the stress corrosion cracking (SCC) growth rate are estimated. In order to check the trend, the process is repeated on three different applied loads. It has been noticed, well studied and proposed that when “local mesh size (MS)” to “embedded crack length (Le)” ratio (MS/Le) ≤ 0.0005 in two of the specimen used, the K and dεdr become smooth and the simulated SCC crack growth results are nearest to the experimental values of the SCC crack growth rate.

Laser glazing of cold sprayed coatings for the mitigation of stress corrosion cracking in light water reactor (LWR) applications

The effect of laser power, traverse speed, and cold spray coating thickness were examined with the goal of mitigating and repairing stress corrosion cracking (SCC) in light water reactor (LWR) environment. For this purpose, SCC-susceptible Alloy 600 substrate material was coated with SCC-resistant Alloy 690 via the cold spray technique. The cold spray coated substrate was then laser-glazed using various laser parameters. Single pass and multiple pass laser glazed regions were created to determine the effects. For this purpose, the area of the fusion zone, depth of the fusion zone, and elemental composition of the cross section were examined by optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy. It was shown that chromium dilution from the laser glazed region into the substrate is not a significant factor in laser glazed cold spray coated samples. Separate laser glazed samples were subjected to ASTM 633C to determine coating adhesion. Finally, by using interrupted SCC crack growth rate tests, it was shown that low traverse speeds and high laser powers produce deep fusion zones within the cold sprayed coating and substrate that can be used to seal pre-existing cracks, thus stopping SCC growth.

Study on the Rate of Elastic-plastic Crack Propagation of Heterogeneous Metal Welded Joints in Nuclear Power

In the high-temperature water environment of nuclear power, austenitic stainless steel, nickel-based alloy materials and welded joints composed thereof are the key locations for environmental cracking (EAC) problems such as stress corrosion cracking (SCC). In order to understand the crack propagation behavior and expansion rate of welded joints under the condition of abrupt and heterogeneous material properties of welded joints, this paper uses the extended finite element technique (XFEM) in the large nonlinear finite element software ABAQUS, based on the elastoplastic material model. Under the condition of welding residual stress field, the effects of different initial crack length and strength mismatch ratio on the crack growth rate of stress corrosion crack under constant load were studied. The results show that the SCC crack growth rate increases with the increase of the initial crack length. When the crack length of the initial welded joint is constant, different mismatch ratio has a certain effect on the crack growth rate. In the low ratio range(less than 1), the crack growth rate also increase if the strength mismatch ratio increase. but the crack growth rate is gradually reduce in high ratio range(more than 1). This indicates that the mismatch ratio of 1 is favorable for crack propagation, and the larger the mismatch ratio, the crack propagation is hindered.

Effects of dendrite axis and fusion boundary on stress corrosion cracking of ER 308 L/SS 304L welds in a high-temperature water environment

This study investigated the effects of dendrite axis and fusion boundary (FB) on the stress corrosion cracking (SCC) of 308 L/304 L welds by using an alternating current potential drop (ACPD) technique to measure the SCC growth rates in a simulated boiling water reactor environment. The results show that the ferrite/austenite interfaces are more susceptible to SCC in the SS 308 L welds. Furthermore, the angle between the applied load and the dendrite axis affects the SCC growth rate, and as this angle approached 90°, the SCC crack growth rate increases. The SCC cracks in the heat affected zone (HAZ) are mainly intergranular and some cracks propagate transgranularly. Furthermore, the primary crack in the HAZ propagates along the FB; when reaching FB, some secondary cracks are arrested at the FB. The residual strain caused by weld shrinkage is the crucial factor for the increase in SCC susceptibility in HAZ.

An Approach to Estimate SCC Growing Rate in Slow Strain Rate Tensile Test Based on EPFEM

The slow strain rate tensile test (SSRT) is a common means to investigate stress corrosion cracking (SCC) in key engineering structural materials of light-water reactors, and it is an important task to real-time monitor the crack growing length and rate of the specimen during the test. Because the specimen is placed in an autoclave with high-pressure and high-temperature water environment-simulated light-water reactor, the current potential drop method, which includes current potential drop (DCPD) and alternating current potential drop (ACPD), is the main means to real-time monitor crack growth rate in the SCC test. As a supplementary means to obtain the crack growth rate during the test, the SSRT process of nickel-based Alloy 600 CT specimens is investigated by using the elastic-plastic finite element method (EPFEM) in this paper. Based on the consideration that both the elastic-plastic deformation and crack length of the specimen would affect the relationship between the load and the displacement of the loading point during the SSRT test, the relationship between the loading point displacement caused by crack propagation ΔLc and plastic deformation ΔLp is separated by EPFEM. Then, the SCC crack growth rate and the real-time crack length are obtained. This proposed approach could be used to improve the test results in the SSRT test.

Quantitatively related acoustic emission signal with stress corrosion crack growth rate of sensitized 304 stainless steel in high-temperature water

Stress corrosion cracking (SCC) of sensitized 304 stainless steel in high-temperature water was in-situ monitored by coupling acoustic emission (AE) and direct current potential drop (DCPD) techniques. The AE signals were identified using novel recurrence quantification analysis (RQA) and k-mean cluster method. It was found that the RQA is feasible to identify the evolution of different AE waveforms generated by ligament tearing and plastic deformation of the crack tip. The AE cumulative hits rate was linear with the SCC crack growth rate, providing a possibility for applying the AE technique to quantitatively evaluate SCC in high-temperature water.

Stress corrosion cracking behavior of warm forged 316L stainless steel at different orientations

Stress corrosion cracking (SCC) behavior of ∼20% warm forged 316L stainless steel (SS) round bar was evaluated for different cracking orientations relative to the applied deformation in hydrogenated and oxygenated high purity water at 325 °C. Different SCC crack growth rates (CGRs) obtained at three orientations demonstrates that the L-R orientation where cracking occurred in the plane of deformation has the highest SCC susceptibility, while the C-L orientation where cracking was oriented to run along the forging direction has the lowest SCC susceptibility. The anisotropic cracking behavior of warm forged 316L SS at different orientations, which is prominent in hydrogenated water, depends highly on the distribution of lamellar plastic strains that are produced during deformation in different planes.

Environmentally assisted cracking of forged 316LN stainless steel and its weld in high temperature water

The corrosion fatigue (CF) and stress corrosion cracking (SCC) crack growth rates (CGRs) of type 316LN SS and its welds that are used for pressurized water reactor primary water components were evaluated. Effects on CGRs of loading condition, water chemistry and metallurgical microstructure were studied. Experimental results indicated that stress intensity factor K, loading ratio, and frequency control the CGRs of materials along with corrosion potential, chloride, and pH also significantly influencing the cracking behavior. Similar CGRs under various conditions were observed in the base metal and its weld, with low SCC susceptibility in hydrogenated water, but high SCC susceptibility in oxygenated water. The weld metal showed lower SCC CGRs than base metal in oxygenated high purity water but shifted to higher values after adding ppb levels of chloride because of the presence of δ-ferrite in the weld.

Analysis on Crack Driving Force at Stress Corrosion Cracking Tip Induced by Scratch in Nickel-based Alloy

To understand the effects of the oxide morphology on the crack tip of scratched surface on stress corrosion cracking (SCC) behavior of nickel-based alloy, the local stress-strain field at scratched crack tip in the presence of film-induced stress was simulated. Results show that wedge force is the major crack driving force that causes the SCC growth. Greater oxide thickness of scratch crack will give rise to larger wedge force and lead to an increase in SCC crack growth rate (CGR). The formation of oxide at crack tip will induce compressive stress, compressive strain and negative strain gradient, and thus retard the SCC propagation in the upper and lower part of the semi-elliptical crack front.

Main mechanical factors affecting creep strain at crack tip of stress corrosion cracking in full life cycle

Stress Corrosion Cracking (SCC) is a failure mechanism that is caused by environment, susceptible material and tensile strain at crack tip. The mechanical state at crack tip is one of the main factors affecting stress corrosion crack propagation rate in structural materials of nuclear power plants. To understand the effect of mechanical factor on creep strain on SCC crack growth rate in the light water reactor environments, the creep strain at crack tip in full life cycle is studied by elastic-plastic finite element method (EPFEM) in this paper. Study results indicate that it is suitable to use the creep strain in front of crack tip as a mechanical factor of SCC behaviors, and also show that wedging stress is the main mechanical factor affecting creep strain in micro crack stage, while external load are gradually becoming the main mechanical factor in long crack stage. Crack propagation rate is very slow in micro crack stage, and it will expand rapidly under the combined effect of residual stress and working load if there is an initial crack l.

Characterizing the effect of creep on stress corrosion cracking of cold worked Alloy 690 in supercritical water environment

The effect of creep on stress corrosion cracking (SCC) was studied by measuring crack growth rates (CGRs) of 30% cold worked (CW) Alloy 690 in supercritical water (SCW) and inert gas environments at temperatures ranging from 450 °C to 550 °C. The SCC crack growth rate under SCW environments can be regarded as the cracking induced by the combined effect of corrosion and creep, while the CGR in inert gas environment can be taken as the portion of creep induced cracking. Results showed that the CW Alloy 690 sustained high susceptibility to intergranular (IG) cracking, and creep played a dominant role in the SCC crack growth behavior, contributing more than 80% of the total crack growth rate at each testing temperature. The temperature dependence of creep induced CGRs follows an Arrhenius dependency, with an apparent activation energy (QE) of about 225 kJ/mol.

A mechanistic study of the temperature dependence of the stress corrosion crack growth rate in SUS316 stainless steels exposed to PWR primary water

Complementary analytical transmission electron microscopy (TEM) and transmission Kikuchi diffraction (TKD) were used to study the influence of temperature on the crack growth rate (CGR) in SUS316 stainless steels. An Arrhenius-type temperature dependence of the CGR has been observed between 250 °C and 320 °C. However, stress corrosion cracking (SCC) CGRs were found to decrease between 320 °C and 360 °C, which cannot be explained in terms of a single operating mechanism. High-resolution characterization has produced direct evidence that the SCC CGR in SUS316 is subjected to, at least, two rate-controlling processes: thermally activated diffusion and mechanical response to external stress and internal strain. While diffusion of metallic and non-metallic species at the crack flanks are enhanced at higher temperatures (350 °C and 360 °C), mechanical response-based mechanisms appear to dominate at lower temperatures (320 °C and 340 °C). Higher strain concentrations and dislocation densities around the crack tip were found at low temperature, potentially leading to accelerated crack growth and a peak in the CGR at ∼320 °C. It is suggested that phenomena occurring near the crack tip can be potentially very different at high and low temperatures.

Effects of chloride and oxygen on stress corrosion cracking of cold worked 316/316L austenitic stainless steel in high temperature water

Cold work of materials, dissolved oxygen and chloride in water are crucial factors that accelerate the stress corrosion cracking (SCC) crack growth rate of stainless steel in high temperature water. Cold worked austenitic stainless steel type 316 and 316L were studied in order to obtain their effects on SCC crack growth rates in 288 and 325°C water. Similar SCC behavior were identified for 316 and 316L. Cold working induced comparatively high crack growth rate up to 10−8mm/s even in hydrogenated water, and the collaboration of dissolved oxygen and chloride in water accelerated the SCC crack growth rates much more significantly.