Corrosion Fatigue Crack Research Articles

Corrosion Fatigue Failure Analysis of a Supporting Pipe Weld in Deaerization Plant

The aim of this work is to reveal the failure mechanism of a supporting pipe weld after 20 years of service in a deaerization plant. The characterization methods included inductively coupled plasma, optical microscopy, scanning electron microscope, X-ray energy dispersive spectrometer, mechanical tests, and finite element analysis (FEA). The results showed that the supporting pipe weld failed by corrosion fatigue cracking. Cracks initiated from the surface pits which were due to corrosion. FEA analysis revealed that stress concentration occurred in the failed weld. This paper brings out the details of the investigation and suggests remedial measures to improve performance of such pipe welds in deaerization plants.

Environmentally assisted cracking and hydrogen diffusion in traditional and high-strength pipeline steels

Abstract This article deals with the risk of environmentally assisted cracking of steel structures that are kept under cathodic protection (CP). The experimental results collected on both hydrogen diffusion and hydrogen embrittlement (HE) of high-strength low-alloy (HSLA) steels under CP are discussed. Hydrogen diffusion was evaluated by permeation experiments and a scanning photoelectrochemical current technique, as a function of microstructure orientation, on both loaded and unloaded specimens. HE tests were carried out under constant load, slow strain rate (SSR tests), and slow bending conditions. Tests were also carried out on several grades of HSLA steel having different microstructures. The results confirm that HE in artificial seawater under CP can occur in steel with tensile yield strength in the range of 400–660 MPa only in the presence of high cathodic polarization and continuous plastically straining conditions. HE susceptibility increased with increasing applied cathodic polarization and with decreasing strain rate. HE susceptibility of the rolled steels at relatively high strain rate (10-4 to 10-5 s-1) increased with the hydrogen diffusion coefficient. Similar results were observed in terms of the HE contribution to corrosion fatigue crack growth rate. High-temperature-tempered martensitic steels showed a lower HE susceptibility.

Fractography of in-Service Fracture of the Metal in Weld Joint No. 111 of the Steam Generator of a WWER-1000 Power Unit

Complex studies on the in-service metal fracture in weld joint No. 111 of the steam generator of a WWER-1000 power unit elucidated the micromechanisms of crack propagation (combination of corrosion cracking and corrosion fatigue). Quantitative measurements of fatigue striation spacings were performed. Real in-service loading conditions of the collector “pocket” zone where corrosion fatigue cracks originate and propagate were estimated.

Corrosion-Fatigue Crack-Growth Resistance of Steel of the Boom of a Clamp-Forming Machine

The kinetics of corrosion-fatigue crack growth in the angle steel of the boom frame of a clamp-forming machine after its operation for 30 yr is studied for a high load ratio in a model medium simulating rainfalls in the industrial regions. For the material in the intact state, we do not reveal the influence of corrosive media on the crack growth rate. At the same time, this influence strongly accelerates the fracture processes in the material after operation, especially within the Paris segment of the kinetic fracture diagrams. In their near-threshold segments, the retardation of crack growth is possible, which is probably connected with the corrosion blunting of its tip. It is shown that the specific fatigue striation in the area of near-threshold crack growth may serve as a fractographic sign of the in-service degradation of the metal of the analyzed structure.

Corrosion Fatigue Behavior of 7A85 Aluminum Alloy Thick Plate in NaCl Solution

The S–N curves of 7A85-T7452 aluminum alloy in laboratory air and in neutral 3.5 wt% NaCl solution were obtained by axial fatigue tests. Results show that the detrimental effect of the aggressive solution was not noticeable at high-cyclic-stress regions, but the effect was significant at low-stress region. Corrosion fatigue mechanism was discussed by corrosion morphology analysis, fracture surface analysis and microstructure characterization. It was found that the corrosion fatigue crack commonly initialed at the localized intergranular corrosion site. TEM analysis showed that the microstructures of 7A85-T7452 aluminum alloy were characterized by fine and homogeneously distributed matrix precipitates, as well as continually distributed anodic grain boundary precipitates. The types of microstructures are the reason for its intergranular corrosion susceptibility. The corrosion fatigue process of 7A85 aluminum alloy in 3.5 wt% NaCl solution can be divided into four stages: the crack initiation stage, the stable growth stage with low and high growth rate and the final rupture stage. The sodium chloride solution mainly affected the crack initiation stage and the stable growth stage with low growth rate, and when the crack growth rate reached a threshold, the effect was reduced.

Effects of Thermally Sprayed Aluminum Coating on the Corrosion Fatigue Behavior of X80 Steel in 3.5 wt.% NaCl

Corrosion fatigue and fatigue crack propagation experiments were conducted using X80 steel (with and without aluminum coating) in 3.5 wt.% NaCl solution. Results show that the aluminum coating could significantly improve the corrosion fatigue life of the steel substrate, and that this influence would be enhanced by decreasing the applied stress. However, the crack growth rate of the aluminum-coated X80 steel was slightly higher than that of bare X80 steel. Therefore, the presence of aluminum coating extends the crack initiation stage, and the inhibiting effect of aluminum coating on crack initiation outweighs its promotion of crack propagation. The acting mechanisms of the aluminum coating on crack initiation and propagation were discussed.

Environment-induced fatigue cracking behavior of aluminum alloys and modification methods

AbstractThis paper reviews the current corrosion fatigue strength issues of light metals, which include the corrosion fatigue cracking behaviors, such as the prior-corrosion pit deformation mechanism, the synergistic interaction between prior-corrosion pits and local stress/strain, the coupling damage behavior under mechanical fatigue loading, and the surrounding environmental factors such as a high humidity and a current 3.5 wt.% or 5.0 wt.% NaCl aqueous solution. The characterization of corrosion fatigue crack growth rate based on simple and measurable parameters (crack propagation length and applied stress amplitude or stress intensity factor) is also of great concern in engineering application. In addition, an empirical model to predict S-N curves of aluminum alloys at the environmental conditions was proposed in this paper. One of the main aims was to outline the corrosion fatigue cracking mechanism, which favors the corrosion fatigue residual life prediction of aluminum alloys subjected to the different environmental media that are often encountered in engineering services. Subsequently, this paper explores recently various surface modification technologies to enhance corrosion fatigue resistance and to improve fatigue strength. For example, the fatigue strength of 2024-T4 aluminum alloy has been modified using plasma electrolytic oxidation coating with the impregnation of epoxy resin modification method to compare with other oxide coating or uncoated substrate alloy.

Effect of saline corrosion environment on fatigue crack growth of 7475-T7351 aluminum alloy under TWIST flight loading

The corrosion fatigue crack propagation was studied on the 7475 T7351 aluminum alloy under a standardized load sequence for flight simulation tests on transport aircraft wing structures (TWIST) simulated loading under a mean stress 80MPa. The corrosive environment in tests was salt spray containing 3.5% and 5.0% NaCl. The results indicated that the specimens tested in salt spray fractured after more flights than the samples tested in air, while the crack propagation rates in corrosion environment showed retardation and acceleration. The microfractures in specimens revealed impressions caused by salt crystals and oxides, which may have slowed the propagation rate, competing with the plastic zone resulting from the loading of the flight.

Biomaterial Real Cracks Evaluation by Eddy Current Testing Method

The paper deals with identification of real biomaterial`s cracks using electromagnetic non-destructive sensing. Advanced types of the magnetic field sensors are used for this purpose. New modular eddy current probe is used for the evaluation. Harmonic excitation is used for the excitation of the eddy currents. The real biomaterial stress corrosion cracks (SCC) and fatigue cracks (FC) are inspected. Gained results are discussed and presented in the paper. The main aim of the paper is to compare the sensitivity of the various magnetic field sensors under the same conditions.

A Novel Modified Paris’ Law Based Evaluation of Fatigue Crack Propagation of LD2 under Combination of Corrosion and Cyclic Loadings

The present thesis made a research to evaluate fatigue crack growth rate subjecting to corrosion and cyclic fatigue loading, with the effect of load frequency on fatigue taken into account. A modified Paris’ law based model is proposed. An exponential modified expression of proportional parameter account for fatigue frequency is proposed based on the obvious fact that low frequency loading will lead to long fatigue life, thus prolong interaction time between corrosion media and specimen which will favor for crack propagation. Loading frequency higher enough will shorten that time, thus influence of corrosion will be significantly weaken, close to pure mechanical fatigue. Crack growth rate prediction from proposed formula is proved to be in good agreement with experimental results for steadily extended corrosion fatigue crack.

Effect of oxidation behavior on the corrosion fatigue crack initiation and propagation of 316LN austenitic stainless steel in high temperature water

The effect of oxidation behavior on the corrosion fatigue crack initiation and propagation of 316LN austenitic stainless steel (SS) in 320°C water and air environments was investigated by corrosion fatigue cracking test system, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and nanoindentation. The experimental results indicated that the cracks were found to be initiated at first 20% of fatigue life of the specimens tested in 320°C water, while only a few cracks were found until fracture when tested in 320°C air. The crack propagation rates of the specimens tested in 320°C water were obviously faster than those tested in 320°C air especially at lower strain amplitude of ±0.5%. This can be attributed to the oxidation behavior of the 316LN SS specimens tested in 320°C water was more serious than those tested in 320°C air. The compositions were more complex of the oxide films formed in 320°C water than those tested in 320°C air, which lead to crack initiation easier in the former. Moreover, the 320°C water made the mechanical properties of the oxide films worse, resulting in a faster fatigue crack propagation rate at crack tip.

Understanding Fatigue Crack Growth Behavior at Low Frequencies for a Mn–Ni–Cr Steel in 3.5 % NaCl Solution Under Controlled Cathodic Potential

Abstract Fatigue crack growth behavior at low loading frequencies for a Mn–Ni–Cr steel immersed in 3.5 % NaCl solution, with and without cathodic polarization, is investigated and presented in this paper. Frequency shedding method is used to estimate fatigue crack growth rate over a range of frequencies between 0.01 and 5 Hz at a constant stress intensity factor range of 15 MPa √m. The effectiveness of cathodic potential of −900 mV SCE in containing corrosion contribution to crack growth is estimated by comparing with published data on fatigue crack growth rate in lab air and 3.5 % NaCl solution without cathodic polarization. It is noted that there are three regions of crack growth rate as a function of applied frequencies when the data is plotted in log–log scale: linear crack growth rate, plateau crack growth rate, and high crack growth rate. The crack growth rate of steel in 3.5 % NaCl solution at 15 MPa √m is scanned for different cathodic potentials between −760 mV SCE and 1150 mV SCE at 0.01 and 0.1 Hz. The potentials at which the crack growth rates are the maximum and the minimum are found to be −760 and −950 mV, respectively. The optimum cathodic protection potential for the minimum corrosion fatigue crack growth rate ranges between −900 and −950 mV. This optimum potential for the minimum corrosion crack growth rate is more negative than the cathodic potential required for restraining the corrosion effects on fatigue strength of steel to normal ambient air behavior.

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.

Effect of Anodic Films on Corrosion Resistance and Fatigue Crack Initiator of 2060-T8 Al-Li Alloy

Effect of Anodic Films on Corrosion Resistance and Fatigue Crack Initiator of 2060-T8 Al-Li Alloy

Localised Corrosion Damage Based Fatigue Crack Extension Model of Aluminium Alloy with Prior Corrosion Damage

A modified model was presented for describing corrosion fatigue crack growth rate of aluminum alloy accurately. Considering the local damage around the crack tip is more reasonable for accelerating crack growth rate under corrosive environment, a damaged influence factors which characterize the damage degree of local damage near the crack tip has been introduced to revise the corrosion fatigue crack growth rate, and the experimental results are in good agreement with predictions of amendment fatigue crack growth rate model. The proposed model based on damaged influence factors is reasonable, and proposed a theoretical reference for aluminum alloy damage tolerance analysis.

Effects of dissolved oxygen on corrosion fatigue cracking of Alloy 690(TT) in pressurized water reactor environments

Alloy 690(TT) is widely used for steam generator tubes in pressurized water reactor (PWRs), where it is susceptible to corrosion fatigue. In this study, the effects of dissolved oxygen on the corrosion fatigue cracking behavior of Alloy 690(TT) in simulated PWR environments were investigated under small scale yielding conditions. Dissolved oxygen, combined with the monotonic plastic zone size (rp), had a significant influence on out-of-plane cracking of corrosion fatigue crack and environment factor (Fen).

Fatigue Crack Propagation Life Prediction of 2A12 Aluminum Alloy Based on VCCT

The fatigue crack propagation behavior of the prior corrosion 2A12 aluminum alloy fastener involving a central hole was investigated. The virtual crack closure technique (VCCT), is straightforward and not sensitive to the FEA mesh size, was carried out to calculate strain energy release rate and SIFs of AA 2A12 under different stress levels and corrosion years. Based on the VCCT, the simulation carried out to analyze the corrosion fatigue crack growth behavior. It was proved to be convenient to simulate the crack propagation life and the predicted crack growth curve was in good agreement with the experimental results.

Methods for the Evaluation of Fracture and Strength of Pipeline Steels and Structures Under the Action of Working Media. Part І. Influence of the Corrosion Factor

We generalize contemporary methods used for the evaluation of strength and fracture hazard of elements of pipeline structures with the use of approaches of fracture mechanics of materials, by taking into account specific features of influence of corrosive factors. The stages of initial corrosion damage to the metal and of the surface corrosion-fatigue cracking in pipeline steels are analyzed. We discover the influence of the chemical composition of the medium, frequency and stress ratio of the loading cycle, and the time of operation on their cyclic corrosion crack resistance. For the expert evaluation of the serviceability and fracture hazard of pipeline systems with corrosion cracklike defects, we propose to use special diagrams containing three characteristics zones: zone of safe operation, zone of operation with predicted development of the existing cracklike defects, and zone of brittle fracture hazard.

Modeling of Corrosion Fatigue Crack Growth of X70 Pipeline Steel and Numerical Simulation of Crack Propagation

To solve the problem that the change of curve slop was not considered in the common corrosion fatigue crack growth, a new corrosion fatigue crack propagation model based on Pairs formula was established in this paper; which corrected parametersCandnof Paris formula at the same time. Based on the fatigue crack propagation experimental data of X70 pipeline steel in hydrogen sulfide corrosive environment, the key parameters of the model were fitted. Based on the new model, a FRANC3D software was used, and the corrosion fatigue crack propagation processes of X70 pipeline steel in corrosive solution were simulated. It was demonstrated that the simulated fatigue crack growth processes obtained by the boundary element method were very close to the test results, and the maximum error is less than 10%. Therefore, boundary element method can be used to predict the life of corrosion fatigue on the project.

Corrosion effects on fatigue crack propagation of stainless steel and its heat affected zone in pH buffer solutions

A corrosion fatigue crack propagation test for 430 stainless steel and its heat affected zone was conducted in pH buffer solutions, and the results were compared with model predictions. The bare corrosion effect on fatigue crack propagation, particularly in corrosive environments was evaluated by means of a modified Forman equation. As shown in the results, the average corrosion rate determined from the ratio of corrosion induced crack length to the entire crack length under a cycle load was 0.11 and 0.37 for the base metal and heat affected zone, respectively, with a load ratio of 0.5, frequency of 0.5, and a pH 10.0 environment. The modeling and experimental processes demonstrate a step towards a methodology enabling the corrosion effects on fatigue crack propagation behavior to be determined.