Stress Corrosion Cracking Process Research Articles

A phase‐field framework for stress corrosion cracking prediction in elastoplastic metallic materials

AbstractTo capture the stress corrosion cracking (SCC) in metallic materials, a phase‐field framework considering localized plastic deformation and stress states is established. A new function of critical energy release rate is proposed to describe the degradation of cracking resistance of materials in the SCC process. This proposed framework can reproduce SCC results consistent with experimental observations in C‐ring steel SCC tests, especially capturing the directionally characteristic of the cracks. Furthermore, the influences of localized plastic deformation and stress states on the SCC process are studied. This novel phase‐field framework can capture (1) the influences of coupled electricity, mechanics to the SCC mechanisms; (2) the contribution of plastic strain energy as the driving force for the phase‐field; (3) the potential and preferential crack initiation and propagation morphology within the complex stress and strain domain; and (4) the dependence of SCC rate and propagation direction on stress state and localized plastic deformation.

A semi-phenomenological dynamics model for full-life predictions of stress corrosion cracking

A semi-phenomenological model mimicking the full-time process of stress corrosion cracking (SCC) is proposed, and its attractive characteristics can be summarised as follows. Firstly, the role played by the hydrostatic pressure gradient at a crack tip in anodic dissolution is centralised by the proposed partial differential equation system, so as to formulate the interplay of load and corrosion in a mechanistic manner. As a result, the model can naturally reproduce the repeated film rupture mechanism that is believed central to general SCC phenomena. Secondly, the model implementation is extremely efficient, outputting a full-life SCC prediction within a few seconds on a normal laptop computer. Thirdly, a general rule for model calibration is introduced against limited experimental data, enabling its predictability over SCC indices that are not experimentally trackable. The efficacy and the generality of the proposed model are examined with three SCC scenarios, including (a) Inconel 600 alloys in nuclear pipelines, (b) stainless steels in oil pipelines, and (c) magnesium alloys used as structural materials in blood vessels. It is shown that SCC indices such as the SCC incubation period, which may be too long to be experimentally measured, can be quickly predicted with the present model after being calibrated.

Hydrogen permeation and SCC susceptibility of X70 pipeline steel in CO2-saturated water environment containing acidic impurity

The effect of HNO3 and H2SO4 impurities on hydrogen permeation behavior and stress corrosion cracking (SCC) susceptibility of X70 steel in CO2-saturated water environment was investigated. Concurrently, a method for characterizing the contribution of corrosion-produced hydrogen to SCC was developed. HNO3 and H2SO4 boost the hydrogen permeation through promoting cathodic hydrogen evolution. The hydrogen embrittlement induced by corrosion-produced hydrogen, together with anodic dissolution, dominates the SCC process of X70 steel. The steel has much higher SCC susceptibility in H2SO4-containing environment than in HNO3-containing environment, which is closely related to the much stronger hydrogen embrittlement effect caused by H2SO4 than HNO3.

In vitro evaluation of stress corrosion cracking susceptibility of PEO-coated rare-earth magnesium alloy WE43

Controlling material degradation in complex mechanobiological environments is the current challenge in advancing biodegradable magnesium implants for orthopaedic applications. Understanding stress corrosion cracking (SCC) mechanisms of magnesium alloy-coating systems in physiological fluids facilitates the design of magnesium implants with excellent biomedical performance. In this study, we investigated the SCC behaviour of a medical grade PEO-coated magnesium alloy WE43 under different loading conditions. Constant loadings tests (CLT) and slow strain rate tests (SSRT) were conducted to evaluate the SCC susceptibility of this alloy-coating system under in vitro conditions. Fracture surfaces of the non-coated and PEO-coated specimens were characterised by scanning electron microscopy to reveal the SCC mechanisms under different loading configurations. The experimental results showed that the alloy-coating system exhibits a high SCC resistance in SSRT conditions. However, high stress levels and plastic deformations lead to a significant acceleration of the SCC process. Moreover, the fracture surface analysis demonstrated that the brittle nature of the PEO coating deteriorates the mechanical integrity of the alloy under critical mechanical loadings, which results in an increased susceptibility towards stress corrosion cracking of the coated WE43.

Stress-corrosion cracking of polypropylene in harsh oxidizing environments

Thermoplastic pipes are widely used in the semiconductor industry, where they are used to drain highly corrosive liquid waste. When exposed to oxidizing environments, thermoplastic pipes can undergo stress-corrosion cracking (SCC), potentially causing them to fail prematurely in the absence of appropriate design and maintenance guidelines. Here, the stress-corrosion cracking behavior of polypropylene, commonly used in waste drainage pipes for dilute sulfuric acid/hydrogen peroxide mixtures (Piranha solutions), is investigated as a function of applied energy release rate. Sub-critical crack growth experiments are performed with compact tension specimens in sulfuric acid/hydrogen peroxide mixtures using a custom constant-force loading system to evaluate the effects of temperature and chemical composition on SCC crack growth. The activation energy for the SCC process is 99.7 ± 15.3 kJ/mol, and the crack growth rate depends sensitively on the concentrations of sulfuric acid and hydrogen peroxide in the mixture. We propose a practical guideline to calculate the service life of polypropylene pipes in Piranha solutions using crack velocity curves and show that accidental exposure to a concentrated Piranha solution can significantly reduce service life.

Failure Analysis of the Crack and Leakage of a Crude Oil Pipeline under CO2-Steam Flooding

This paper presents the failure analysis of the crack and leakage accident of a crude oil pipeline under CO2-steam flooding in the western oilfield of China. To analyze the failure behavior and cause, different testing, including nondestructive testing, chemical composition analysis, tensile property testing, metallographic analysis, and microanalysis of fracture and chloride stress corrosion cracking (SCC) testing, are applied in the present study. The obtained results showed that the pipeline under the insulation layer of high humidity, high oxygen content, and high Cl− environment occurred pit corrosion, and the stress concentration area at the bottom of the corrosion pit sprouted cracks. Besides, it is demonstrated that the cracks were much branched, mostly through the crystal, and the fracture showed brittle, which is consistent with the typical characteristics of chloride SCC. Meanwhile, the insufficient Ni content of the pipeline material promoted the process of chloride SCC, and the high-temperature working conditions also aggravated the rate of chloride SCC. In addition, efficient precautions were provided to avoid fracture.

Imidazoline behavior as corrosion inhibitor in the electrochemical characterization of SCC behavior of an API X70 steel exposed to brine solution

Abstract The effect of concentration of an organic imidazoline as inhibitor on internal stress corrosion cracking (SCC) behavior of an API X70 pipeline steel exposed to a brine solution was studied. The SCC process using simultaneously the slow strain rate stress test (SSRT) and electrochemical measurements was performed. Fracture surface analysis and secondary cracking were observed through a scanning electron microscopy (SEM). According to SEM fractography and SSRT results, the steel showed high SCC susceptibility with a brittle fracture and several secondary cracks without addition of inhibitor, whereas the addition of inhibitor to brine solution was effective to increase the SCC resistance of steel at concentrations of inhibitor of 50 and 100 ppm. A further addition of concentration of inhibitor had a negative effect on the mechanical properties of the steel. Electrochemical measurements results are in accordance with the SCC susceptibility, indicating that corrosion inhibitor film suppressed the anodic and cathodic reactions increasing the resistance to SCC until concentration of 100 ppm. Further addition of inhibitor aggravated the localized corrosion due to local desorption of inhibitor molecules. The Hilbert–Huang transform (HHT) analysis revealed the contribution of different corrosion process contained in the electrochemical current noise (ECN) signals at several inhibitor concentrations.

Electrochemical Noise of SCC Inhibition of a Supermartensitic Stainless Steel in Sour Solution

In this work, the inhibition effect of a non-ionic gemini surfactant, named bis(2-((2-palmitoamidoethyl)amino)ethyl)1H-imidazole4,5-dicarboxylate, on the stress corrosion cracking (SCC) behavior of a supermartensitic stainless steel (SMSS) was studied in sour environment. The slow strain rate stress tests (SSRT) results and fractographic analysis revealed that the corrosion inhibitor was able to inhibit the SCC process using a concentration above than 5ppm. At concentrations of 0 and 5 ppm, the steel showed a brittle fracture with susceptibility to SCC, whereas at concentrations of 25 and 100 ppm, the fracture was ductile, and the steel was practically immune to SCC. The EN measurements showed transients associated with pits and microcracks, which were confirmed by SEM examination. The EN analysis using the shot noise theory indicated that localized corrosion was the dominant corrosion process at the concentrations of inhibitor in which the SMSS was susceptible to SCC.

Nucleation and propagation of stress corrosion cracks: Modeling by cellular automata and finite element analysis

The stress corrosion cracking process of pipeline steel was modeled using cellular automata and finite element analysis, the initiation and propagation of the cracks were simulated. Before the initiation of cracks, the extent of pitting corrosion was revealed to be controlled by anodic reactions and mechanical factors, in which electrochemical corrosion played a leading role. The deposition of corrosion products created a diffusion barrier between the reactants participating in the corrosion process, limiting the rate of electrochemical reactions. During the crack propagation process, the mechanochemical effects caused by plastic deformation promoted anodic dissolution at the crack tip, driving crack propagation.

Effect of icosahedral phase formation on the stress corrosion cracking (SCC) behaviors of the as-cast Mg-8%Li (in wt.%) based alloys

Through exploring the stress corrosion cracking (SCC) behaviors of the as-cast Mg-8%Li and Mg-8%Li-6%Zn-1.2%Y alloys in a 0.1 M NaCl solution, it revealed that the SCC susceptibility index (ISCC) of the Mg-8%Li alloy was 47%, whilst the ISCC of the Mg-8%Li-6%Zn-1.2%Y alloy was 68%. Surface, cross-sectional and fractography observations indicated that for the Mg-8%Li alloy, the α-Mg/β-Li interfaces acted as the preferential crack initiation sites and propagation paths during the SCC process. With regard to the Mg-8%Li-6%Zn-1.2%Y alloy, the crack initiation sites included the I-phase and the interfaces of I-phase/β-Li and α-Mg/β-Li, and the preferential propagation paths were the I-phase/β-Li and α-Mg/β-Li interfaces. Moreover, the SCC of the two alloys was concerned with hydrogen embrittlement (HE) mechanism.

Interpreting electrochemical noise signal arising from stress corrosion cracking of 304 stainless steel in simulated PWR primary water environment by coupling acoustic emission

Electrochemical noise (EN) signals arising from stress corrosion cracking (SCC) of 304 stainless steel (SS) in borated and lithiated high-temperature water were monitored. Acoustic emission (AE) signals were simultaneously measured to relate the EN signals with the SCC process. Through Weibull analysis of the EN signals, it was demonstrated that the EN technique can in-situ capture the SCC events in high-temperature water. With evolution of the SCC process, Hilbert time-frequency spectrum of the EN signals gradually migrated from high frequency to low frequency. The capacity of EN and AE techniques to monitor the SCC process in high-temperature water is compared.

Effect of ultrasonic impact treatment on microstructure and corrosion behavior of friction stir welding joints of 2219 aluminum alloy

Ultrasonic Impact Treatment (UIT) was performed to improve the corrosion resistance of 2219 aluminum alloy friction stir welding (FSW) joints. Results showed that the coarse grains on near surface of FSW joints were obviously modified and refined after UIT, and the thickness of the modified layer of different sub-regions was ranged from 90 to 120 μm. UIT increased intergranular corrosion resistance of 2219 aluminum alloy FSW joints in salt spray corrosion atmosphere. Free-corrosion potential of heat-affected zone (HAZ), which presented the worst corrosion resistance, was increased from −0.653 to −0.628 V, and the corrosion current density was decreased from 7.48 to 6.18 mA cm−2. The sensitivity index of stress corrosion cracking (SCC) of the joints was decreased from 0.139 to 0.129 in 3.5% NaCl solution after UIT, and the risk of crack initiation during SCC process was significantly inhibited. UIT improved the SCC resistance of 2219 aluminum alloy FSW joints by surface plasticity improvement, grain refinement and precipitates dissolution and redistribution.

Influence of microstructure on stress corrosion cracking of X100 pipeline steel in carbonate/bicarbonate solution

The stress corrosion cracking (SCC) behaviors of X100 pipeline steels with different heat-treated microstructures in carbonate/bicarbonate solution at various potentials were investigated in this study. Several analyses were performed using electrochemical measurements, slow strain rate tensile (SSRT) tests, scanning electron microscopy (SEM), and electron back-scattered diffraction (EBSD). The results showed that the SCC susceptibilities of heat-treated microstructures increase as the cathodic potential shifts from −850 to −1200 mVvsSCE. At a weak cathodic potential, the different microstructures show clear SCC sensitivity, showing that hydrogen cannot be ignored in this circumstance when the alkaline environment is not considered seriously. At a mild cathodic potential, hydrogen sensitivity controls SCC behavior, but at a larger negative potential, both electrochemical effect and hydrogen sensitivity influence SCC behavior. The SCC cracks propagate along the high angle grain boundary (HAGB) at open circuit potential (OCP) and as the applied potential is adjusted negatively, the cracks would either follow low angle grain boundary (LAGB), HAGB or random orientation propagation paths. The synergistic influence of dislocation, grain boundary, grain size, martensite/austenite (M/A) island, and carbide controls the SCC process of the X100 pipeline. SCC susceptibility was shown to be high in microstructures with coarse grain and high dislocation density, whereas grain boundaries such as the martensite/austenite (M/A) island and carbide offer sites for SCC initiation.

Effect of heat treatment on the stress corrosion cracking behavior of cast Mg-3Nd-3Gd-0.2Zn-0.5Zr alloy in a 3.5 wt% NaCl salt spray environment

This study was undertaken to investigate the influence of heat treatment on the stress corrosion cracking (SCC) behavior of a low-pressure sand-cast Mg-3Nd-3Gd-0.2Zn-0.5Zr alloy in a 3.5 wt% NaCl spray environment. Results indicated that T4 heat treatment (540 °C × 10 h) could effectively improve the corrosion resistance, compared with as-cast and T6 alloys. The relatively lowest volume fraction of high-potential (HPOT) phases observed in the T4 alloy primarily accounts for its lowest corrosion rate. Slow strain rate tensile (SSRT) tests were conducted to evaluate the influence of heat treatment states on the SCC resistance. The lowest SCC susceptibility index ( I SCC I = 0.403 and I SCC II = 0.165) was obtained in T4 state, while the as-cast alloy possessed the highest SCC susceptibility. The present work revealed that hydrogen-assisted cracking (HAC) played a key role in the SCC process. Cracking was effectively suppressed in the T4 alloy owing to its retarded hydrogen diffusion. The structure and compositions of the multi-layer corrosion product film were characterized in detail. Solution treatment applied in this work was confirmed to promote the formation of protective and dense RE oxides layer, primarily contributed to the relatively highest SCC resistance achieved in the T4 alloy. • SCC susceptibility decreases in the order of as-cast > T6 > T4. • HPOT phase dissolution and hydrogen-diffusion suppression strongly improve the SCC resistance. • The structure of multi-layer corrosion product film is established. • Protective RE-oxides layer is characterized by SIMS.

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.

About the role of the hydrogen during stress corrosion cracking of a low-copper Al-Zn-Mg alloy

This study provides some clarifications about the influence of microstructural parameters on the susceptibility of low-copper Al-Zn-Mg alloy to stress corrosion cracking (SCC). Tensile tests in air were carried out on AA7046 in T4 and T4 aged at 150 °C (named 150/20) metallurgical states after pre-exposure of the specimens to a chloride solution under mechanical loading. The results showed the predominant role of the corrosion-induced hydrogen during SCC process on the loss of elongation to failure. Scanning kelvin probe force microscopy (SKPFM) measurements were performed for the T4 specimens as well as for a 530 °C heat-treated T4 specimen with a coarse-grained microstructure; this allowed the contribution of hydrogen diffusion at the grain boundaries on the hydrogen distribution to be highlighted. The analysis of the fracture modes after tensile tests and hydrogen diffusion profiles obtained by SKPFM in the framework of previous studies investigating the microstructure-hydrogen and plasticity-hydrogen relationships allowed to propose a qualitative model to describe SCC phenomena. The detrimental role of hydrogen at the grain boundaries on the mechanical behaviour was highlighted; the outcome of the evaluation of results from the present study in combination with our previous studies and literature data suggested that it can be limited by hydrogen trapping on intragranular η-MgZn2 precipitates.

Study of SCC of X70 Steel Immersed in Simulated Soil Solution at Different pH by EIS.

An electrochemical study of stress corrosion cracking (SCC) of API X70 steel in a simulated soil solution at different pH values (3, 8 and 10) was carried out. The stress conditions were implemented by slow strain rate stress test (SSRT) and the SCC process was simultaneously monitored by electrochemical impedance spectroscopy (EIS). Fracture surface analysis and corrosion product analysis were performed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The results show that the susceptibility to SCC was higher as the pH decreases. In the acid solution, hydrogen evolution can occur by H+ and H2CO3 reduction, and more atomic hydrogen can diffuse into the steel, producing embrittlement. EIS results indicated that the anodic dissolution contributed to SCC process by reducing the charge transfer resistances during the SSRT test. While SEM micrographs shown a general corrosion morphology on the longitudinal surface of samples. At higher pH (pH 8 and pH 10), the SCC susceptibility was lower, which it is attributed to the presence of corrosion products film, which could have limited the process. Using the angle phase (φ) value it was determined that the cracking process started at a point close to the yield strength (YS).

A coupled mechano-chemical peridynamic model for pit-to-crack transition in stress-corrosion cracking

We introduce a coupled mechano-chemical peridynamic model to describe stress corrosion cracking. In this model, two mechanisms, stress-dependent anodic dissolution and diffuse corrosion layer-assisted fracture, are considered to influence pitting and crack propagation in stress corrosion cracking. Diffusion peridynamic bonds (acting as dissolution bonds at the solid/liquid interface) and mechanical peridynamic bonds are used to represent the interactions between material points. Mechanical bonds can be damaged by mechanical stretching or by anodic dissolution. The magnitude of the dissolution fluxes for diffusion peridynamic bonds depends on both mechanical deformation and the applied electrical potential. The coupling between anodic dissolution and mechanical damage leads to cracks that initiate in the corrosion damage layer and propagate into the bulk. A 2D three-point bending/corrosion test demonstrates the concept. We verify the model in 3D using an experimental test from the literature for the case of stress-corrosion cracking process in a steam turbine steel sample. The model's results capture the pit-to-crack transition time, the pit size and shape at fracture, as well as the morphology of cracks that spring from, and connect the pits.

Localized Corrosion and Stress Corrosion Cracking Behavior of AA7003 in a 3.5 wt% NaCl Aqueous Solution

The microstructure, localized corrosion (LC) and stress corrosion cracking (SCC) behavior of 7003 aluminum alloy (AA7003) under various aging treatments (peak aging (PA), double peak aging (DPA), regression and re-aging (RRA)) were investigated by means of transmission electron microscope (TEM), scanning electron microscopy (SEM), electrochemical impendence spectroscopy (EIS) and slow strain rate tensile test. The results of TEM showed a discontinuous distribution of grain boundary precipitates of AA7003 under DPA and RRA treatments, which is beneficial for increasing the resistance of LC and SCC. Meanwhile, LC was found initiating firstly on intermetallics which caused the dissolution of surrounding matrix, then pitting holes were formed and developed into matrix. In addition, the SCC process of AA7003 could be divided into two stages, i e, initial pre-cracking and breeding cracking. The EIS analysis, cross-section morphologies and fracture surfaces of specimens indicated that DPA and RRA treatments significantly decreased the crack growth rate during breeding cracking stage, especially for RRA treatment.

Stress Corrosion Cracking of 2205 Duplex Stainless Steel with Simulated Welding Microstructures in Simulated Sea Environment at Different Depths

The stress corrosion cracking (SCC) of 2205 duplex stainless steels (DSSs) with different microstructures in simulated sea environments were studied by electrochemical measurements, electron backscattered diffraction and slow strain rate tensile tests. Heat treatments were used to obtain different microstructures. The DSSs were held at 1350 and 850 °C for 30 min and then quenched in the water. The results showed that the DSSs had a higher SCC susceptibility in simulated shallow sea environment than in the simulated deep-sea environment. Electrochemical mechanism of the SCC process was controlled by environment factors (temperature, hydrostatic pressure and dissolved oxygen content). The mechanisms of SCC changed from anodic dissolution in the simulated shallow sea environment to hydrogen embrittlement in the simulated deep-sea environment. Moreover, the quenched DSSs, especially the steel held at 850 °C, were more vulnerable to SCC than as-received steel in the simulated sea environment due to the deterioration of the microstructure.