Corrosion Fatigue Crack Growth Research Articles

The Effect of Fatigue Damage on the Corrosion Fatigue Crack Growth Mechanism in A7N01P-T4 Aluminum Alloy

A7N01P-T4 aluminum alloy plates for high-speed trains will experience a certain amount of fatigue damage under alternating loads. Three groups of samples, P0 (no fatigue damage), P1 (loading stress 30 MPa), and P2 (loading stress 70 MPa), were created, and corrosion fatigue crack growth (CFCG) tests were conducted in 3.5 wt.% NaC1 solution. The crack growth rate was found to increase after fatigue damage as the damage degree increased. In addition, the A7N01P-T4 aluminum alloy base metal exhibited obvious secondary cracks and crack bifurcations after fatigue damage. It is believed that fatigue damage causes stress concentration in the material, while a certain degree of stress corrosion cracking occurs during the CFCG growth process. This is because hydrogen (H) easily accumulates and diffuses along the grain boundary, which reduces the strength of the grain boundary, thereby becoming the preferred orientation for crack growth. This explains why the CFCG rate of the material is accelerated following fatigue damage to a certain extent.

Constitutive model for corrosion fatigue crack growth in 3D parts

Constitutive model for corrosion fatigue crack growth in 3D parts

Effect of thermal aging on the environmental assisted cracking behavior of 308L weld metal in high temperature water

The effect of thermal aging on environmental assisted cracking (EAC) of 308 L weld metal was investigated. Experimental results reveal that thermal aging promotes corrosion fatigue (CF) crack growth with extensive inter-dendritic cracking, but has a limited effect on the stress corrosion cracking (SCC) growth under constant loads. The higher crack tip strain rate and the enhanced preferential oxidation of deteriorated δ-ferrite are responsible for the enhanced CF susceptibility after thermal aging. The dispersed δ-ferrites and the decreased crack tip strain rate account for the high SCC resistance under constant load regardless of the thermal aging.

Study on corrosion fatigue behavior of heavy piece Ti6Al4V titanium EBW joint in artificial seawater

Titanium alloy has been more and more used in the ocean engineering field. Since the crucial service environment, the corrosion fatigue behavior of the Ti6Al4V alloy EBW joint has been investigated and analyzed. The results show that the grain size of the molten zone decreases gradually from the central line to the base metal symmetrically and the acicular α’ martensite and β phase grain boundaries are the dominating phases of the seam zone. Moreover, the corrosion fatigue crack growth rate of the seam zone was insensitive to the texture of the base metal and crystal orientation of the ti6al4v alloy. It could also be seen that the base metal and the seam zone have different crack growth mechanisms, which is mainly during to the existence of the acicular α‘ martensite in the seam zone and the trend of crack tip energy release. The crack propagation rate of the seam is lower than that of the base metal.

Development of a new approach for corrosion-fatigue analysis of offshore steel structures

Corrosion-fatigue is known to be the dominant failure mechanism in offshore structures, such as offshore wind turbines, due to the constant exertion of cyclic loads in highly corrosive environments. In the present study, the existing corrosion-fatigue crack growth (CFCG) theories and models have been firstly reviewed and discussed, and subsequently a new approach has been proposed to accurately describe the corrosion-fatigue behaviour under various loading conditions and frequencies. To examine the validity of the proposed approach, fatigue crack growth experiments were conducted on S355G10+M medium strength steel compact tension, C(T), specimens at different load levels and frequencies. The experimental data were initially analysed using the traditional fracture mechanics parameter ΔK which was shown to have limitations at elucidating the effects of frequency on CFCG rates in the range of 0.2–0.5 Hz. Therefore, a new fracture mechanics parameter was developed that allows these effects to be seen and accounted for more clearly. Furthermore, a new CFCG model was developed, using the introduced fracture mechanics parameter, for predicting the crack growth rates in seawater from the short-term test data in air. The proposed model has been found to correlate well with experimental data from corrosion-fatigue experiments on S355G10+M from this study and S355J2+N structural steel data available in the literature.

Corrosion fatigue crack growth prediction of bridge suspender wires using Bayesian gaussian process

This paper proposes a Bayesian gaussian process-based corrosion fatigue damage assessment framework for bridge suspender wires. Prior statistical parameters in the fatigue life prediction model are obtained by corrosion fatigue crack growth test under different stress ratios. A numerical simulation method of corrosion fatigue crack growth is developed combined with ABAQUS and FRANC3D. Following this, a Bayesian network-based framework is established by integrating fatigue crack growth model, stress concentration factor and observed fatigue crack length information to reduce the uncertainties. The uncertainties exist in stress concentration factor are quantified by gaussian process regression-based surrogate model, and the pit geometry of length, width and depth are selected as three-dimensional input. Markov Chain Monte Carlo simulation is used to obtain the posterior distribution of parameters in the Bayesian network. The results show that the fatigue crack growth predictions agree well with experimental observations. The proposed method can simplify the complicated modeling process of stress concentration factor under the influence of corrosion pit, and can effectively update the model parameters to accurately predict the corrosion fatigue crack of bridge suspender wires.

Fatigue assessment of fillet weld in steel bridge towers considering corrosion effects

Field inspection shows that the fillet weld in steel bridge towers may be subjected to corrosion and fatigue loading simultaneously. To ensure the structural safety in the service life, corrosion effects on the fatigue life of the fillet weld in steel towers were investigated in this study. A prediction procedure of the fatigue life of the weld was firstly proposed based on the fracture mechanics method and verified by the test results. Three types of corrosion effects, pitting corrosion at the initial crack, pitting corrosion near the initial crack, and the corrosion fatigue crack growth were considered. Three corrosion levels were also defined under different corrosive environments. By taking the Third Nanjing Yangtze River Bridge as an example, a modified finite element (FE) model integrated with the local shell model was established to analyze the stress variation of the fillet weld in steel towers. Based on the stress influence lines, the maximum stress range was obtained under the vehicle load. Fatigue assessment of the fillet weld was finally performed considering the corrosion effects. The result shows that the remaining fatigue life of the fillet weld was greatly reduced by the corrosion pits at the initial crack or the interactions of corrosion and fatigue. However, since the tensile stress range was small in the steel bridge towers, the fatigue performance of the fillet weld considering the corrosion effects can still meet the requirements of the code specification.

Effect of Microstructure on the Corrosion Fatigue Crack Growth of Low and Medium Steels

This article studies the effect of microstructure on the corrosion fatigue crack growth behavior of low and medium carbon steels. 45 steel and 15CrMo were selected and five typical microstructures were obtained by different heat treatment processes. The microstructures of 45 steel and 15CrMo after annealing and normalizing are both ferrite and pearlite, but the proportions of ferrite and pearlite in the four microstructures are different. The quenching and tempering microstructure of 45 steel is tempered fine pearlite. Corrosion fatigue tests were conducted on specimens with different microstructures of the two materials. Expressions of corrosion fatigue crack growth rate and da/dN∼ΔK fitting curves of different microstructures were obtained. Comparison of da/dN∼ΔK curves of 45 steel shows that tempered fine pearlite has the best resistance to corrosion fatigue crack growth, and the content of pearlite has a great impact on the corrosion fatigue crack growth behavior for specimens with the microstructure of ferrite and pearlite. In the low ΔK region, the corrosion factor plays a dominant role in fatigue crack growth, and the corrosion resistance of pearlite is weak, which leads to a higher da/dN in the normalized state. In the high ΔK region, fatigue factor dominants, since the fatigue resistance of pearlite is strong, da/dN of the annealed state is higher. The experimental results of 15CrMo showed the same crack growth rate change regulation as that of 45 steel, which further proves the effect of pearlite on the corrosion fatigue crack propagation behavior.

Fatigue Crack Growth of Z2CND18-12N Austenitic Stainless Steel and Its Heat-Affected Zone in a Dissimilar Metal Weld Joint in 325°C Water

Fatigue crack growth (FCG) in Z2CND18-12N austenitic stainless steel and its heat-affected zone (HAZ) in the Z2CND18-12N/16MND5 dissimilar metal weld joint has been investigated in room temperature air and 325°C water. The dependence of FCG rates on specimen orientation in room temperature air got somewhat evident as ΔK decreased to 13 MPa√m. However, for Z2CND18-12N steel, the influence of specimen orientation on the FCG in room temperature air and the corrosion fatigue crack growth (CFCG) in 325°C water was slight and negligible. A moderate increase in the FCG rate was observed for the Z2CND18-12N HAZ in room temperature air at a low ΔK = 13 MPa√m (near ΔK threshold), compared with its base metal. However, the CFCG rate difference between the Z2CND18-12N HAZ and its base metal was minor. The CFCG in the Z2CND18-12N in 325°C water (without the addition of H2) was consistent with a slip-oxidation-rupture mechanism and the oxide film on the corrosion fatigue crack tip mainly consisted of Fe3O4.

Corrosion-fatigue crack growth behaviour of wire arc additively manufactured ER70S-6 steel parts in marine environments

A crucial part of the structural integrity assessment of marine structures is the analysis of the fatigue crack growth behaviour of the welded joints in seawater environments, where the cracks often initiate and propagate under corrosion-fatigue loading conditions. In recent years, technological developments have facilitated the fabrication of steel components and structures using additive manufacturing technologies. Among the existing technologies, the Wire Arc Additive Manufacturing (WAAM) technique has proven to offer great potentials for fabrication of large-scale structures. The present study investigates the corrosion-fatigue crack growth (CFCG) behaviour of the WAAM parts fabricated using ER70S-6 low carbon steel wire to assess the suitability of this technology for future marine structures. In this experimental study, the cracking behaviour and test duration in corrosion-fatigue tests were investigated and analysed in conjunction with the microstructural examination of the tested specimens. Moreover, the obtained results were compared with the recommended trends available in BS7910 standard for conventional welded joints and the data available in the literature on widely used offshore structural steel weldments. The CFCG results obtained from this study contribute to the overall knowledge and design requirements for the new optimised functionally graded structures made with WAAM technology for marine applications.

Effect of microstructural heterogeneity on corrosion fatigue crack growth behavior of 60-mm thick-plate TC4 titanium alloy NG-GTAW welded joint

The microstructure, mechanical properties and corrosion fatigue crack growth behavior of 60-mm thick-plate TC4 titanium alloy narrow gap gas-tungsten arc welding (NG-GTAW) welded joints applied to the shell of the Jiaolong deep submersible were studied, and the effect of microstructural heterogeneity on the corrosion fatigue crack growth behavior was discussed. The results show that significant microstructure evolution occurred in the welded joint with acicular α′ martensite coarsening and a random orientation distribution. The hardness and tensile strength distribution of the welded joints correspond to the difference in the microstructure, with a smaller size and more randomly oriented α′ martensite providing superior strengthening effect. The acicular α′ martensite of the weld metal (WM) has excellent resistance to crack growth compared to the α and β phases of the base metal (BM). The degree of crack serration depends on the size and orientation distribution of the α grains and acicular α′ martensite. As the stress increases, the fatigue resistance of BM may have a more serious deterioration trend compared with WM.

Titanium alloy corrosion fatigue crack growth rates prediction: Peridynamics based numerical approach

This study presents a numerical approach for modelling the Corrosion Fatigue Crack Growth (CFCG) in conventional casting and additively manufactured Ti6Al4V alloys. The proposed numerical model, based on Peridynamics (PD), combines the PD Fatigue Crack Growth (FCG) model and PD diffusion model in order to couple the mechanical and diffusion fields existing in the material due to the impact of environmental fatigue. The mechanical field is responsible for the characterisation of the changes to the structure due to the fatigue loading conditions. The diffusion field is based on the modelling of the adsorbed-hydrogen Stress Corrosion Cracking (SCC), in particular, the Hydrogen Embrittlement (HE) model is considered. The proposed approach has been validated using experimental data available in the literature showing the capability of the tool to predict the CFCG rates.

Corrosion fatigue crack growth of serviced API 5L X56 submarine pipeline

Corrosion fatigue tests on standard compact tensile (CT) specimens extracted from API 5L X56 pipe-in-pipe pipeline after servicing for 15 years have been conducted in air and in seawater environment (corrosion fatigue) respectively. Effects of maximum load, stress ratio and loading frequency on the fatigue crack growth (FCG) rate are considered in the fatigue tests, and such effects were investigated and discussed based on the tested results. The maximum load has a remarkable influence on the fatigue life of CT specimens. However, it has a slight effect on the two constants in Paris’ law. Stress ratio has a significant influence on the FCG in middle stage, and FCG rate decreases with the stress ratio increases. With the increase of loading frequency, FCG rates decrease and fatigue life increase. Using scanning electron microscope, the fracture surface of the fatigue crack is observed and analyzed, and transgranular cleavage fracture is found on the fracture surface. The effects of the maximum load, the stress ratio and the loading frequency on the crystal surface and on the FCG mode were analyzed and compared based on such observation on the fracture surface of the fatigue crack.

Corrosion-fatigue crack growth behaviour of wire arc additively manufactured ER100S-1 steel specimens

The wire arc additive manufacturing (WAAM) technology is a promising fabrication technique which has been proven to have many advantages for producing large structures; however, the fatigue and corrosion-fatigue performance of WAAM steel components for application in the marine environments is still unexplored. In this study, the WAAM technique was employed to fabricate four specimens made of ER100S-1 steel, which were then tested under cyclic loading conditions in seawater to assess the corrosion-fatigue crack growth (CFCG) behaviour and hence suitability of this fabrication technology for offshore renewable energy applications. The test duration, cracking mechanisms and CFCG rate were investigated for each specimen and the material’s behaviour was investigated by considering the microstructural examinations. Furthermore, the obtained results were compared with the BS7910 standard recommended trends and experimental data available in the literature for conventionally built weldments made of different grades of steel which are commonly used for offshore applications.

Effects of orientation on the fatigue crack growth behaviors of the ZK60 magnesium alloy in air and PBS

Strong anisotropic corrosion and mechanical properties caused by specimen orientations greatly limit the applications of wrought magnesium alloys. To investigate the influences of specimen orientation, the corrosion tests and (corrosion) fatigue crack growth tests were conducted. The rolled and transverse surfaces of the materials show distinct corrosion rate differences in the stable corrosion stage, but the truth is the opposite for the initial stage of corrosion. In air, specimen orientations have a significant influence on the plastic deformation mechanisms near the crack tip, which results in different fatigue fracture surfaces and cracking paths. Compared with R-T specimens, N-T specimens show a slower fatigue crack growth (FCG) rate in air, which can be attributed to crack closure effects and deformation twinning near the crack tip. The corrosion environment will not significantly change the main plastic deformation mechanisms for the same type of specimen. However, the FCG rate in phosphate buffer saline (PBS) is one order of magnitude higher than that in air, which is caused by the combined effects of hydrogen-induced cracking and anodic dissolution. Owing to the similar corrosion rates at crack tips, the specimens with different orientations display close FCG rates in PBS.

An improved crack growth model of corrosion fatigue for steel in artificial seawater

Corrosion will greatly reduce the fatigue life of steel structures. Based on the Paris equation and continuum damage mechanics, an improved crack growth model is obtained by introducing corrosion damage into the Paris equation. The derivation and calculation procedure of the improved Paris equation are discussed in detail. The proposed model was used to calculate the corrosion fatigue crack growth length of S690 in 3.5 wt% NaCl solution. The model demonstrates good accuracy and predicts the corrosion fatigue life of T-welded joint specimens in artificial seawater.

Role of Plastic Damage in Corrosion Fatigue Crack Growth of A7n01p-T4 Aluminum Alloy

Role of Plastic Damage in Corrosion Fatigue Crack Growth of A7n01p-T4 Aluminum Alloy

Effect of heat treatment on fatigue crack growth behavior of 316NG austenitic stainless steel in deaerated water at 325 °C

316NG (00Cr17Ni12Mo2N) austenitic stainless steel was heat-treated at 600, 725 and 1000 °C to investigate the effects of heat treatment temperature and holding time on the fatigue crack growth behavior of this steel in deaerated water at 325 °C. It is found that fatigue crack growth rates in air at room temperature are decreased after the heat treatments, due to a reduced dislocation density. Corrosion fatigue crack growth rates in water at 325 °C are also decreased after the heat treatments at 600 and 1000 °C for 1 h, while the heat treatment at 725 °C leads to a moderate increase in the fatigue crack growth rate. The latter phenomenon results from a higher amount of CrNbN (Z-phase) precipitates formed in the steel after the annealing at 725 °C.

Effects of heat treatment on corrosion fatigue and stress corrosion crack growth of additive-manufactured Alloy 800H in high-temperature water

Crack growth behaviour of additively manufactured (AM) Alloy 800H were studied under cyclic and static load in high-temperature water, focusing on heat treatment effects. Under cyclic loading, heat treatment gently affected corrosion fatigue. The growth rate is comparable to wrought 800H. As the load cycle frequency reduced to below 0.001 Hz, AM 800H exhibited inconsistent stress corrosion cracking response as compared to wrought 800H. Depending on heat treatment, inhomogeneous crack propagation and localized pinning were observed in stress-relieved and recrystallized AM 800H, attributed to carbides, microstructural inhomogeneity, and twin boundaries. Grain boundary sensitization at ˜10 wt% Cr caused fast crack growth.

Corrosion-Fatigue Crack Growth Performance of Titanium Grade 29 Welds in Tapered Stress Joints

Abstract Design of a steel catenary riser requires the use of connection hardware to decouple the large bending moments induced by the host floater at the hang-off location. Reliability of this connection hardware is essential, particularly in applications involving high pressure and high temperature fluids. One option for this connection hardware is the metallic tapered stress joint. Titanium (Ti) Grade 29 has been identified as an attractive material candidate for demanding stress joint applications due to its “high strength, low weight, superior fatigue performance and innate corrosion resistance”.2 Titanium stress joints for deepwater applications are typically not fabricated as a single piece due to titanium ingot volume limitations, thus making an intermediate girth weld necessary to satisfy length requirements. As with steel, the potential effect of hydrogen embrittlement induced by cathodic and galvanic potentials must be assessed to ensure long-term weld integrity. This paper describes testing from a joint industry project (JIP) conducted to qualify titanium stress joint (TSJ) welds for ultra-deepwater applications under harsh service and environmental conditions. Corrosion-fatigue crack growth rate (CFCGR) results for Ti Grade 29 flat welding-groove weld (1G/PA) gas tungsten arc welding (GTAW) specimens in seawater under cathodic potential and sour brine under galvanic potential are presented and compared to vendor recommended design curves.