Stress Corrosion Cracking Mechanism Research Articles

Crack Chemistry Control of Intergranular SCC in Sensitized Al-Mg

Fracture mechanics experiments and occluded crack chemistry modeling validate the mechanism for intergranular stress corrosion cracking (IGSCC) of sensitized Al-Mg alloys: dissolution of discontinuous grain boundary β (Al3Mg2) precipitates activates Al-Mg (α) solid solution dissolution to acidify the crack solution for crack tip hydrogen embrittlement. Slow-rising displacement experiments with precracked specimens establish the strong effect of applied potential on IGSCC kinetics for sensitized AA5083-H131 (S-L orientation, 22 mg/cm2) in neutral NaCl solution. Anodic polarization increases growth rates through enhanced α dissolution for crack acidification and H uptake, whereas cathodic polarization below the pH-sensitive α breakdown potential reduces growth rates by limiting Al dissolution, and thus crack acidification and the overpotential for H production (ηH). Polarization below the β breakdown potential eliminates IGSCC by precluding β dissolution and crack acidification. Cathodic polarization could ...

Degradation mechanisms and evaluation of failure of gas pipelines

This paper presents the degradation mechanisms and their effect on lifetime of Gas Transmission Pipelines (GTP). The degradation mechanisms of US, Europe, Russian and Lithuanian GTP are presented. Lithuanian GTP is described in more detail. The experimental testing of mechanical properties and fracture parameters of selected pipelines were carried out. The fracture mechanic analysis was performed for segment of gas transmission pipeline of Lithuania. The acceptable and critical cracks sizes were determined. Also Stress Corrosion Cracking (SCC) mechanism was analysed and cracks sizes at witch SCC could be expected were determined. For simulation of defects R6 option 1 method was used.DOI: https://dx.doi.org/10.5755/j01.mech.21.5.10196

Stress corrosion cracking assessment of API X65 steel non‐conventionally heat treated

Stress corrosion cracking (SCC) susceptibility of API X65 steel non‐conventionally heat‐treated was evaluated through slow strain rate tests (SSRTs) using the synthetic soil solution NS4 at 20, 40 and 60 °C. Polarization curves (PCs) and corrosion potential (Ecorr) measurements were also performed. The non‐conventional heat treatment (HT) was made by heating plates at 1050 °C for 30 min followed by water quenching. The tensile strength of the heat‐treated plates increased to values similar to API X80 steel. The SCC index obtained by ratios of mechanical properties indicated that X65 steel without HT is not susceptible to SCC whereas with HT is slightly susceptible to SCC. The SCC mechanism in the soil solution in the heat‐treated plates was influenced by hydrogen diffusion as confirmed by the internal cracks and the brittle fracture observed in the specimens. The electrochemical study suggests that the corrosion process of X65 steel with and without HT occurs via a mix mechanism where the charge transfer resistance is influenced by a mass transfer process. Crevice corrosion features were found in the surface of the steel. It is likely that this type of corrosion could have sensitized the X65 steel and induced cracks when the steel was under tensile stress.

Stress corrosion cracking of E690 steel as a welded joint in a simulated marine atmosphere containing sulphur dioxide

Stress corrosion cracking (SCC) behavior and mechanism of E690 welded joint in simulated marine atmosphere containing SO2 were investigated using SSRT method and electrochemical measurements. Results showed that it had very high SCC susceptibility in this environment with a combined mechanism of anodic dissolution and hydrogen embrittlement (HE). The intercritical heat affected zone in the welded joint was the most vulnerable location to SCC because this zone has less strength, more negative potential, and higher corrosion current density. The M-A constituents had a detrimental effect on SCC behavior in the synergetic effect of stress concentration, micro-galvanic corrosion, and HE.

Quasi-static behavior of notched Ti-6Al-4V specimens in water-methanol solution

Abstract The adoption of Ti-6Al-4V titanium alloy is widespread in advanced engineering fields, such as the aerospace, automotive, and maritime sectors, due to its remarkable mechanical characteristics and proven corrosion resistance. However, literature studies and field failures have underlined that the Ti-6Al-4V is susceptible to the stress corrosion cracking (SCC) and the corrosion fatigue phenomena in methanol-water solutions. Although several studies focused on the SCC behavior of this particular titanium alloy, recent corrosion fatigue experiments (R=0.1) on Ti-6Al-4V specimens in a water-methanol environment have highlighted a sensible decrease in maximum applied stress of up to 50% and a high sensitivity even to low methanol concentrations. In the present work, an experimental quasi-static SCC test campaign in water-methanol mixture at different concentrations has been conducted on flat dogbone Ti-6Al-4V specimens. The results have been compared with recent corrosion fatigue experiments to characterize the different damage mechanisms at play and decouple mechanical and chemical driving forces. The micromechanical behavior of the material has been analyzed, highlighting the role of the microstructure in the SCC mechanism. Failure surfaces have been investigated with scanning electron and optical microscopy.

Stress corrosion cracking of a high-strength friction-stir-welded joint of an Al–Zn–Mg–Zr alloy containing 0.25 wt.% Sc

Stress corrosion cracking (SCC) behavior and mechanism of a friction stir welded Al–Zn–Mg–Zr alloy with 0.25wt.% Sc were investigated. Impurity intermetallics and primary Al3ScxZr1−x particles both crack perpendicular to tensile direction, whereas anodic dissolution only occurs around the former, initiating SCC. During cracking propagation, both anodic dissolution and hydrogen embrittlement operate. The thermo-mechanically affected zone on advancing side adjacent to weld nugget zone is most susceptible to SCC, which can be ascribed to the enrichment of impurity intermetallics, continuously distributed grain boundary precipitates and its stronger galvanic coupling with weld nugget zone from their greater microstructure and micro-chemistry differences.

Influence of Aging Treatments on Alterations of Microstructural Features and Stress Corrosion Cracking Behavior of an Al-Zn-Mg Alloy

7xxx series Al-Zn-Mg-(Cu) alloys have higher strength in their peak-aged (T6) states compared with other age-hardenable aluminum alloys; however, the maximum strength peak-aged state is more susceptible to stress corrosion cracking (SCC) which leads to catastrophic failure. The over-aged (T7) temper with 10-15% lower strength has higher resistance to SCC requiring oversized structural aerospace component applications. The medium-strength AA7017 Al-Zn-Mg weldable alloy without Cu is also prone to SCC under certain environmental conditions. In the present investigation, the SCC behaviors of an AA7017 Al-Zn-Mg alloys of different tempers have been assessed. Specific aging schedules have been adapted to an AA7017 alloy to produce various tempers, e.g., under-, peak-(T6), over-(T7), and highly over-aged tempers. Artificial aging behavior of the AA7017 alloy has been characterized by hardness, electrical conductivity measurements, x-ray diffraction, differential scanning calorimetry, and electrochemical studies. Slow strain rate test technique was used to assess the SCC behaviors of the AA7017 alloys of under-, T6, T7, and highly over-aged tempers in 3.5 wt.% NaCl solution at free corrosion potential (FCP) and at applied anodic potential, as well. Results revealed that the AA7017 alloy tempers are not susceptible to SCC in 3.5 wt.% NaCl solution at FCP, but severely damaging to SCC at applied anodic potentials. Microstructural features, showing a non-recrystallized grain structure and the presence of discrete, widely spaced, not-interconnected η precipitates at the grain boundaries, are the contributive factors by virtue of which the alloy tempers at FCP did not exhibit SCC. However, the applied anodic potential resulted in rapid metal dissolution from the grain boundary region and led to SCC. The local anodic dissolution (LAD) is believed to be the associated SCC mechanism.

Finite element analysis of stress corrosion cracking for copper in an ammoniacal solution

Finite element analyses including a cohesive zone model (CZM) were conducted to investigate the role of corrosion product films (CPFs) in stress corrosion cracking (SCC) for copper in an ammoniacal solution. It is found that a tensile CPF-induced stress generates near the interface between the CPF and the copper substrate at the substrate side in front of the notch tip for a U-shaped edge-notched specimens. The CPF-induced stress is superimposed on the applied stress to enhance emission and motion of dislocations. The peak opening stress (S 11) increases with an increase in CPF thickness and a decrease in CPF Young’s modulus. Damage mechanics based on the CZM was applied to study the stress corrosion crack initiation and propagation by analyzing the stress redistributions and load–displacement curves. The results show that the crack initiates first in the CPF and then propagates to the copper substrate. The fracture strain of the specimen covered a CPF is lower than that without a CPF. Based on the simulation results, the mechanism of the CPF-induced SCC, which promoted the initiation and propagation of the stress corrosion cracks, was discussed.

The effects of dissolved hydrogen on the corrosion behavior of Alloy 182 in simulated primary water

The effects of dissolved hydrogen (DH) on the corrosion behavior of Alloy 182 in high temperature (320°C) water were studied using in situ electrochemical measurements and ex situ surface analyses. The film resistance and thickness increased with decreasing DH. Under conditions of DH=50cm3/kg and 30cm3/kg, the oxide film was very thin and predominantly consisted of Cr3+. At DH=5cm3/kg, the oxide film grew thicker, and the outer part consisted of NiO and spinel, with Cr3+ primarily located in the inner part. The underlying mechanism of stress corrosion cracking (SCC) susceptibility was considered.

A New Understanding of Stress Corrosion Cracking Mechanism of X80 Pipeline Steel at Passive Potential in High-pH Solutions

Susceptibilities to stress corrosion cracking (SCC) of X80 pipeline steel in relatively concentrated carbonate/bicarbonate solutions with different chloride ion concentrations or pH value at a passive potential of −200 mV vs SCE were investigated by slow strain rate tensile test. In order to explore the SCC mechanism and the evaluation criterion for the SCC susceptibility of the steel in passive state, electrochemical measurements were taken. Potentiodynamic polarization curves were obtained at different potential sweep rates, and electrochemical impedance spectroscopy measurements were taken after fast polarization to the passive potential. The effects of chloride ion and pH on SCC behaviors of X80 steel at the passive potential were also discussed. The results showed that the SCC mechanism of X80 pipeline steel was greatly influenced by the passive film formed in these solutions. The SCC behaviors followed the film suppressed anodic dissolution mechanism in these circumstances, because the filming process accounted for a considerable proportion of the overall electrode process. The criteria for evaluating the SCC susceptibility of the steel at passive potential were proposed and validated. Decreasing in the concentration of chloride ion or increasing in pH value resulted in the reduction in SCC susceptibility. The existence of chloride ion greatly lowered the passivation tendency and the film stability, while its concentration determined the dissolution rate of the steel matrix. Higher pH value was responsible for the stable and tenacious passive films and the high repassivation capability. It was also inclined to lower the anodic dissolution rate at crack tips by retarding the cathodic oxygen reduction.

Crack growth rate in core shroud horizontal welds using two models for a BWR

An empirical crack growth rate correlation model and a predictive model based on the slip–oxidation mechanism for Stress Corrosion Cracking (SCC) were used to calculate the crack growth rate in a BWR core shroud. In this study, the crack growth rate was calculated by accounting for the environmental factors related to aqueous environment, neutron irradiation to high fluence and the complex residual stress conditions resulting from welding. In estimating the SCC behavior the crack growth measurements data from a Boiling Water Reactor (BWR) plant are referred to, and the stress intensity factor vs crack depth throughout thickness is calculated using a generic weld residual stress distribution for a core shroud, with a 30% stress relaxation induced by neutron irradiation. Quantitative agreement is shown between the measurements of SCC growth rate and the predictions of the slip–oxidation mechanism model for relatively low fluences (5×1024n/m2), and the empirical model predicted better the SCC growth rate than the slip–oxidation model for high fluences (>1×1025n/m2). The relevance of the models predictions for SCC growth rate behavior depends on knowing the model parameters.

Stress corrosion cracking investigation of high Co‐Ni secondary hardening ultra‐high strength steel in neutral 3.5 wt% NaCl solution

Stress corrosion cracking (SCC) and passivation behaviour of ultra‐high strength steel 23Co14Ni12Cr3 in neutral 3.5 wt% NaCl solution were investigated by slow strain rate test, surface analysis techniques and electrochemical measurements. The passive film on the steel is mainly composed of Fe, Co, Cr and Ni oxides and hydroxides. At potentials less than −850 mVSCE, SCC is controlled by hydrogen induced cracking (HIC). The passive film decreases SCC susceptibility of the steel at −400 mVSCE. While, HIC plays a dominant role on SCC mechanism at OCP.

Review on stress corrosion and corrosion fatigue failure of centrifugal compressor impeller

Corrosion failure, especially stress corrosion cracking and corrosion fatigue, is the main cause of centrifugal compressor impeller failure. And it is concealed and destructive. This paper summarizes the main theories of stress corrosion cracking and corrosion fatigue and its latest developments, and it also points out that existing stress corrosion cracking theories can be reduced to the anodic dissolution (AD), the hydrogen-induced cracking (HIC), and the combined AD and HIC mechanisms. The corrosion behavior and the mechanism of corrosion fatigue in the crack propagation stage are similar to stress corrosion cracking. The effects of stress ratio, loading frequency, and corrosive medium on the corrosion fatigue crack propagation rate are analyzed and summarized. The corrosion behavior and the mechanism of stress corrosion cracking and corrosion fatigue in corrosive environments, which contain sulfide, chlorides, and carbonate, are analyzed. The working environments of the centrifugal compressor impeller show the behavior and the mechanism of stress corrosion cracking and corrosion fatigue in different corrosive environments. The current research methods for centrifugal compressor impeller corrosion failure are analyzed. Physical analysis, numerical simulation, and the fluid-structure interaction method play an increasingly important role in the research on impeller deformation and stress distribution caused by the joint action of aerodynamic load and centrifugal load.

Corrosion and stress corrosion cracking of ultra-high-purity Mg5Zn

This paper reports on the measurement of the corrosion rate, and the stress corrosion cracking threshold stress, for ultra-high-purity Mg–5Zn. The corrosion rate was higher than the intrinsic corrosion rate of ultra-high-purity Mg, attributed to the quality of the corrosion product film. The threshold stress for stress corrosion cracking, at an applied stress rate of 0.00016MPas−1, was equal to 0.7 times the yield stress in air. The ductility of the cracking indicated that the stress corrosion cracking mechanism was probably hydrogen enhanced localized plasticity.

Comparative Evaluations on Stress Corrosion Cracking Mechanism of Low Alloy Ultra-High Strength Steels in Neutral 3.5 wt% NaCl Solution

Comparative Evaluations on Stress Corrosion Cracking Mechanism of Low Alloy Ultra-High Strength Steels in Neutral 3.5 wt% NaCl Solution

Stress corrosion cracking (SCC) failure in marine areas of fixed guards for climbing

This work studies the particular mechanism of environmental stress corrosion cracking (SCC) that has been described to interest stainless steel products, like climbing anchors, installed in sea areas. The failure analysis of several broken anchors was carried out. The samples were collected in different parts of the world, always from climbing structures close to the sea. The analysis confirmed the stress corrosion mechanism of degradation, giving also important information about the specific environments causing the metal fracture. These results are in agreement with a few previous works about this subject and are in the frame of the larger topic of SCC of austenitic stainless steel at room temperature. Moreover, some corrosion tests were carried out on stainless steel samples simulating the operation conditions, after contamination with electrolytes at different concentration. The tests are performed in order to better understand the degradation mechanism and to evaluate the influence of some environmental parameters over the susceptibility to SCC. With these experimental data, a possible interpretation model has been proposed together with some reasonable solutions for the material selection process, considering the problem’s characteristics and the multiple alternatives available nowadays for climbing materials.

Stress Corrosion Cracking of X80 Pipeline Steel Under Various Alternating Current Frequencies in High-pH Carbonate/Bicarbonate Solution

The effect of various alternating current (AC) frequencies on stress corrosion cracking (SCC) behavior and mechanism of X80 pipeline steel was investigated in high-pH carbonate/bicarbonate solution by polarization curves and slow strain rate tensile tests. With decreasing AC frequency, the passivity of the steel degrades and the SCC susceptibility increases, especially at the low-frequency AC of 30 Hz. With or without various AC frequencies, the difference in the SCC behavior and mechanism of the steel in the solution is remarkable. In the absence of AC superimposition, the crack is intergranular and the SCC mechanism is anodic dissolution. In contrast, under various AC frequencies, the fracture mode is transgranular, and the mechanism is controlled by anodic dissolution and hydrogen embrittlement.

SCC damage evolution on martensitic stainless steel by using acoustic emission technique

In the present work, acoustic emission testing (AE) technique was successfully applied to identify damage phenomena occurred during stress corrosion cracking (SCC) in chloride-containing environment of a precipitation hardening martensitic stainless steel. Through the use of multi-variable statistical analysis [by coupling principal component analysis (PCA) and self-organising map (SOM)], the different stages of SCC mechanisms (i.e. activation, growth and propagation of cracks) have been identified and analysed. In particular each mechanism was related to specific and significant AE patterns allowing its univocal recognition.

Heat Treatment as a Method for Excluding IGSCC for Dn300 RBMK-1000 Pipeline Welded Joints

Results are given for research performed in order to substantiate an optimum heat treatment regime with the aim of eliminating defect development by an intergranular stress corrosion cracking (IGSCC) mechanism in a Dn300 pipeline welded joint heat-affected zone.

Further study on crack growth model of buried pipelines exposed to concentrated carbonate–bicarbonate solution

This paper develops and validates a physical crack growth model for stress corrosion cracking and corrosion fatigue for pipelines exposed to concentrated carbonate–bicarbonate solution, assuming that the crack growth is dominated by repeated rupture of passive film at the crack tip. A further analysis indicates that the crack growth in gas line is controlled by the stress corrosion cracking mechanism but the crack growth of liquid line is governed by the corrosion fatigue mechanism. Both cyclic-loading-enhanced stress corrosion cracking and mechanical fatigue may affect the crack growth. Finally, the procedure for field application is outlined.