Corrosion Fatigue Crack Propagation Rate Research Articles

Corrosion fatigue crack propagation behavior of S135 high–strength drill pipe steel in H2S environment

Abstract Corrosion fatigue crack propagation (CFCP) tests were employed to investigate the behavior of S135 low carbon high−strength drill pipe steel under different strain rates in a simulated H2S containing drilling environment. Results revealed that the CFCP rate curve of the S135 steel has the characteristics of stress corrosion and corrosion fatigue (CF), which can be divided into near threshold, platform and rapid propagation zone. H2S has an obvious acceleration effect on the CFCP rate of S135 steel, the propagation rate of S135 steel in H2S solution is about 10 times more than that of in air. The stress ratio R has different effects on rapid propagation and near threshold zone. In the rapid propagation zone, the order of CFCP rate from high to low is R = 0.1 > R = 0.3 > R = 0.5, while the order of near threshold zone just shows the opposite. In the near threshold zone, the CFCP rate increases with the increasing of the stress ratio R. Based on the proposed Corrosion–Passivation–Fracture model and elastic fracture mechanics, the CFCP rate expression of S135 steel in H2S solution is d a d N cf = 1.927 × 10 ‐ 9 Δ K − 6.15 1 − R 0.59 2 , which can be used to predict the CFCP life in practical engineering. Fracture analysis results shows that the CFCP of S135 steel in H2S solution is mainly controlled by anodic dissolution and hydrogen embrittlement.

Stress corrosion cracking and corrosion fatigue cracking behavior of A7N01P‐T4 aluminum alloy

A modified single edge notch tension (SENT) specimen exposed to saline environment was used to investigate the stress corrosion cracking and corrosion fatigue cracking behavior of A7N01P‐T4 aluminum alloy. The crack propagation rate was determined, the microstructure, crack growth path, and the fracture surfaces of specimens were examined by optical microscopy (OM) and scanning electron microscopy (SEM). The results showed that the stress corrosion cracking rate of A7N01P‐T4 alloy in 3.5% NaCl was three orders lower than that of corrosion fatigue crack propagation rate. Mg and Zn segregation at the grain boundaries increased the stress corrosion crack susceptibility. The grain orientation had a significant effect on the crack propagation performance, and the high angle grain boundaries were susceptible to cracking. Hydrogen embrittlement was the primary cause of stress corrosion crack and corrosion fatigue crack propagation.

Corrosion Fatigue Crack Propagation Rate Characteristics for Weldable Ship and Offshore Steels with Regard to the Influence of Loading Frequency and Saltwater Temperature

Abstract After Vosikovsky (1975), the corrosion fatigue crack growth rate (CFCGR) characteristics have been divided into three regions. The region-III rates are very close to mechanical fatigue crack growth rates. CFCGR formulae, including the long-crack length effect (in region I only), the loading frequency effect (in region II only), and the saltwater temperature effect, have been proposed. It has been assumed that CFCGR is proportional to f-k, where f is the loading frequency and k is a constant. The averaged k-value for all steels of yield stress (YS) below 500 MPa, usually with ferrite-pearlite microstructures, is higher than that for YS > 500 MPa, usually with quenched and tempered microstructures. The temperature effect does not appear in region I below room temperature. In the remaining cases, that is, in region I for elevated temperatures and in region II for both low and elevated temperatures, the CFCGR increases with increasing temperature. Under a potential of -0.8 V, a long-crack-length effect, qualitatively similar to analogous effect for free corrosion conditions, appears.

The influence of metallurgical factors on corrosion fatigue strength of stainless steels

Corrosion fatigue strength of stainless steels is controlled by tangled interaction among environmental, mechanical and metallurgical factors. In order to estimate corrosion fatigue strength it is indispensable to understand the role of an each influencing factor. The aim of this paper is to present briefly surveyed results on metallurgical factors on corrosion fatigue strength of stainless steels such as austenitic, martensitic and duplex stainless steels mainly based upon author’s experimental results. The targeted dominant metallurgical factors focussed upon are chemical compositions, heat treatment, manufacturing process and microstructures.The emphasis is placed upon effect of Molybdenum content on corrosion fatigue strength of austenitic stainless steels in 3%NaCl aqueous solution, tempering temperature on corrosion fatigue strength of 13% Chromium stainless steel in 3%NaCl aqueous solution and volume percent ferrite on corrosion fatigue strength of duplex stainless steel in potassium alum aqueous solution. The surface and fracture surface observation by optical and scanning electron microscopy revealed that corrosion pit formed at corrosion fatigue crack initiation area. In light of relatively smaller effect of corrosive environment on corrosion fatigue crack propagation rate it can be surmised that corrosion fatigue strength of stainless steels is governed by crack initiation process. It can be concluded that corrosion fatigue strength of stainless steels is strongly influenced by metallurgical factors such as chemical compositions, heat treatment, manufacturing process and microstructures.The information obtained in this survey directly lead to prevention of corrosion fatigue failure in stainless steels made components, selection of stainless steels in corrosive environments and development of corrosion resistant stainless steels.

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.

선체구조 Ballast Tank 고장력 TMCP강판의 과방식중 부식피로균열 전파거동

Abstract For the steel structures those are used in harsh sea environments, corrosion fatigue is a challenging issue in connection with design life. In this research, in order to investigate the influence of cathodic overprotection on the corrosion fatigue crack propagation behavior, corrosion fatigue crack propagation test under the condition of -950mV vs SCE was conducted by using of high tensile TMCP steel plate and the relationships between da/dN-ΔK were obtained. At this test, when ΔK is low, the crack propagation rates were accelerated compared to those of seawater condition, however, when ΔK is high, the crack propagation rates were lower than those of seawater condition. As the cause for the acceleration and deceleration of corrosion fatigue crack propagation rates under the condition of cathodic overprotection, the role of hydrogen and calcareous deposits are discussed. Key Words : Fracture Mechanics, Corrosion Fatigue, Cathodic Overprotection, Synthetic Seawater 본 논문은 울산과학대학교 연구과제로 수행되었음.

Corrosion Fatigue Crack Propagation of High-strength Steel HSB800 in a seawater environment

Fatigue and corrosion fatigue crack propagation behaviors of high-strength steel, HSB800, were investigated in air and seawater environments. Three-point bending fatigue tests were conducted under various loading conditions at different levels of load frequency and ratio. A fracture model enabling mechanisms-based prediction of corrosion fatigue crack propagation is presented. The results obtained from the model follow the experimental data very well. Validation of the model was also conducted by comparison with other models that used in the analyses of corrosion fatigue crack propagation rates. As shown in results, the corrosion fatigue crack propagation rates ina seawater environmentwere higher than those in air condition underevery loadingconditions. These higher corrosion fatigue crack propagation rates were made possibly by the mechanisms of hydrogen embrittlement together with anodic dissolution.

Comparative evaluation of environment induced cracking of conventional and advanced steam turbine blade steels. Part 2: Corrosion fatigue

Corrosion fatigue crack propagation rates have been determined for two steam turbine blade steels, PH13-8, a candidate steel for advanced turbines, and FV566, typical of conventional turbine blades. The testing was undertaken in simulated condensate environment, 300 ppb Cl − and 300 ppb SO 4 2 - , at 90 °C using trapezoidal loading with a rise time of 20 min to simulate two-shifting (switching on- and off-load on a daily basis). Aerated and deaerated conditions were tested, the former being more representative of the retained aeration in the chamber as the system comes on load. In aerated solution at Δ K = 20 MPa m 1/2 the cyclic crack growth rate for the PH13-8 steel was about a factor of two lower than that for the FV566 steel but the reverse was true for deaerated solution. In both cases, the difference in growth rates diminished with increasing Δ K. Although the cyclic crack growth rate is high the number of cycles per annum is small and the direct impact on overall life may be modest, but not insignificant. The observed cracking behaviour is best explained by a hydrogen assisted cracking mechanism.

Corrosion Fatigue of Aircraft Aluminum Alloy Structure in the Coastal Environment and Improvements

Corrosion-fatigue failure of aluminum alloy stringer on the tour airplane servicing in the coastal environment of the Fiji Islands was discussed. Through analysis on surface topographies and components of aluminum alloy structure and consideration of service environment, it showed that the chloride ions, the aging failure of structure coating and the applied stress are the main reasons for corrosion fatigue failure of aircraft aluminum alloy structure. The corrosion-fatigue crack propagation rate of structural components in the coastal environment was analyzed by derivation of crack expansion formula. Findings showed that the corrosion-fatigue crack will expand rapidly until the structure fractures after the aircraft aluminum alloy structure operates nearly 10800 cycles during the crack growth phase. According to the corrosion-fatigue failure analysis of aluminum alloy structure, some improvements were proposed to slow down the corrosion-fatigue failure of aluminum alloy structure in the coastal environment.

Modelling the crack propagation rate for corrosion fatigue at high frequency of applied stress

The application of standard mathematical techniques for the solution of mass transport equations, in the case of advection that is caused by the pulsating movement of crack walls in the case of corrosion fatigue, can be very time consuming. This problem arises, due to the requirement that the time step that must be employed, when solving the non-stationary equations numerically, must be significantly smaller than the period of oscillation. For overcoming these time-consuming limitations, a simple algorithm, which is based on eliminating the convective term from the equations of mass transfer in the pulsating slab by a suitable change of variables, was developed. The estimation of the advection effect on the rate of corrosion fatigue has been performed for the cases of diffusion and mixed kinetic control at high frequencies of applied stress. It is shown that, in many cases, it is possible to use codes that were developed for describing stress corrosion cracking, i.e. for the case of mass transfer without advection at zero loading frequency, to predict corrosion fatigue crack propagation rate, by simply substituting an effective crack length. Numerical calculations that have been performed in this work also show that the method developed here yields results that are applicable not only to the elevated frequencies, but to the any arbitrary frequency from 0 to ∞ for estimating corrosion fatigue crack propagation rate.

A fracture model of corrosion fatigue crack propagation of aluminum alloys based on the material elements fracture ahead of a crack tip

In this study, attempts were made to extend the concept of material elements fracture ahead of a crack tip during fatigue crack propagation (FCP) to corrosion fatigue crack propagation (CFCP) of aluminum alloys in a corrosive environment. Considering the effect of corrosion damage on the material elements, anodic dissolution and hydrogen embrittlement, a corrosion-blunting-fracture model for CFCP was developed. The expression for the CFCP rate, (d a/d N) cf = B cf(Δ K − Δ K thcf) 2, which reveals the correlation between the CFCP rate and stress intensity factor range, the CFCP threshold, loading frequency, anodic dissolution rate and hydrogen embrittlement of the material elements, is thus derived. The test results and analysis of the CFCP rates of LY12CZ and LC4CS aluminum alloys show that the expression for the CFCP rate gives a good fit to the test results of the CFCP rates in a 3.5% NaCl environment at loading frequency 10 Hz and stress ratios from 0.1 to 0.7. The analysis results of other aluminum alloys 7075-T7651 and 7049-T73 obtained by the CFCP rate expression are in good agreement with the test results of the CFCP rates in a 3.5% NaCl environment at loading frequencies from 0.1 to 10 Hz and a constant stress ratio.

The influence of nitrogen content on corrosion fatigue crack growth behavior of duplex stainless steel

The effect of nitrogen content on the corrosion fatigue crack growth (FCG) behavior of 22% Cr duplex stainless steel (DSS) in chloride solution was investigated. Corrosion fatigue crack growth rate measurements employing fracture mechanics specimens were performed in chloride containing solution. The experimental results showed that the tensile strength and elongation of 22% Cr DSS increased with an increasing amount of nitrogen (range: 0.103–0.195 wt.%) in DSS. Furthermore, nitrogen also caused increases in the microhardness of both ferrite and austenite. The experimental results indicated that the FCG rates of 22% Cr DSSs in 3.5 wt.% NaCl solution at 80°C were higher than that in air. The results revealed that nitrogen in the range of 0.103–0.195 wt.% did not significantly affect the FCG rate of 22% Cr DSS in air and in 3.5 wt.% NaCl solution at 80°C, at 1 Hz. However, at a frequency of 0.1 Hz and in 3.5 wt.% NaCl solution at 80°C, a higher FCG rate was found in the low-N DSS (0.103 wt.% N) compared with those with high nitrogen content (>0.153 wt.% N). As the nitrogen content increased, the content of ferrite phase, which was susceptible to hydrogen embrittlement, in DSS decreased. As a result, the corrosion fatigue crack propagation rate was reduced.

Effect of microstructure on fatigue properties of steels in Sea Water

In this study, fatigue crack propagation properties in sea water are investigated, when considering the usage for hull structural steels. The rate of the optimum ferrite-bainite (F/B) steels shows superior resistance even in a sea water.Corrosion fatigue properties in sea water are investigated for both conventional ferrite-pearlite (F/P) steels and the F/B steels. It is clarified that fatigue strength of the F/B steels is higher than that of the F/P steels. As to corrosion fatigue crack propagation rates, the F/B steel originally has much superior resistance in normal conditions, and acceleration factors of corrosion crack propagation rate in sea water to that of air is almost constant regardless of microstructure in steels. These two characters brings superior propagation resistance in sea water. As to corrosion fatigue strength, the F/B steel has the advantage of not only a long fatigue crack propagation life, but also long fatigue crack initiation life. This extended initiation life in the F/B steel comes from the small number of corrosion pits, which might be corrosion fatigue crack initiation sites. This difference of pit number may depend on homogeneity to general corrosion. In case of the F/P steels, the microstructure is not so homogeneous, therefore, general corrosion is not uniform. In case of the F/B steels, the general corrosion is uniform because of fine and homogeneous microstructures.

An analysis of the effects of sulphur content and potential on corrosion fatigue crack growth in reactor pressure vessel steels

The present work characterizes the effects of sulphur content and applied potential on the corrosion fatigue crack propagation rate in nuclear reactor pressure vessel steels. The data for the characterization were achieved by conducting the tests on A533B type steels, subjected to a sine-waveform loading at 0.0167 Hz in stagnant PWR Primary (Li/B dosed) water at 290°C. Data analyses reveal that both plateau corrosion fatigue crack propagation rate, d a/d N p, and threshold stress intensity factor, Δ K thp, are closely proportional to the square root value of bulk sulphur concentration in the range 0.003-to 0.019%. These relationships have been supported by other sources of data obtained under similar testing conditions. Available experimental results also show that both d a/d N p and Δ K thp are linear functions of the difference between externally applied potential and open circuit potential, Δ E. An equation has been proposed to predict the synergistic effect of sulphur content and applied potential on the plateau corrosion fatigue crack growth rate of A533B steels.

Relation between CF crack propagation rate and dissolution rate at a crack tip for iron in 3.5%NaCl solution

One of the aims of corrosion fatigue (CF) is to predict the crack propagation process. This paper relates the CF crack propagation rate with the dissolution rate at the crack tips for iron in a 3.5% NaCl solution. The results show that the crack propagation rate caused by corrosion factors is much greater than the expected dissolution rate of material at the crack tip.

A Comparison of the Near-Threshold Corrosion Fatigue Crack Propagation Rates in Mil S-24645 HSLA Steel and Its Weld Metal

Near-threshold corrosion fatigue crack propagation studies have been conducted using compact tension specimens of Mil S-24645 HSLA steel and a compatible weld metal in air, ASTM seawater at the free corrosion potential, and ASTM seawater with −0.8V and −1.0V (SCE) cathodic protection. Tests were conducted at 10 Hz and a stress ratio, R = 0.1. The weld metal exhibited slower crack growth rates and higher threshold stress intensity ranges in both air and ASTM seawater than the base metal. However, the weld metal itself exhibited similar behavior in air, ASTM seawater and under cathodic protection, giving a threshold stress intensity range of 10 to 12.7 ksi in1/2 (11 to 14 MPa m1/2). With the exception of the weld metal tested in air, after correction for crack closure, the effective threshold stress intensity range was reduced to the range 3.2 to 5.0 ksi in1/2 (3.5 to 5.5 MPa m1/2). Metal wedges, approximately 5 to 10 μm (1–2 grain sizes), which developed during the tests, were observed to contribute to crack closure in the −1.0V (SCE) cathodically protected specimens.

Environmental cracking of AISI 4145 steel in drilling muds

The environmental cracking of a quenched and tempered AISI 4145 steel in a water-based drilling mud has been investigated under slow strain-rate tensile and cyclic-loading conditions. The variables investigated were pH, potential, temperature and the addition of copper- and zinc-containing lubricants. These tests were supported by detailed electron fractography. Under tensile loading conditions, progressive loss of ductility occurs with decreasing potential and pH, and with increasing temperature. The addition of 25 wt% copper- and zinc-containing lubricants generally reduces this embrittlement. The corrosion fatigue crack propagation rate increases with decreasing potential and pH. At low ΔK values, temperature does not affect the corrosion fatigue crack propagation rate, but it is accelerated by increasing temperature at higher ΔK levels. In the presence of copper-containing lubricant, the crack growth rate is always lower than that in copper-free mud. The addition of zinc-containing lubricant to the mud accelerates the crack growth rate at low ΔK values, but does not affect it at higher ΔK values. It is concluded that the decrease in ductility and the increase in the fatigue crack growth rates in drilling muds, relative to air, are due to the appearance of brittle forms of fracture (intergranular, transgranular and quasi-cleavage fracture modes) which are the result of hydrogen-induced cracking.

炭素鋼の腐食疲労強度に及ぼす窒化チタン被覆の影響

In order to investigate the effect of titanium nitride (TiN) coating on corrosion fatigue behavior of metal, cantilever-type rotating bending corrosion fatigue tests were carried out in 3.0% saline solution by using the round bar specimens of 0.37%C carbon steel, JIS S35C, coated with TiN by the physical vapour deposition (PVD) method or the chemical vapour deposition (CVD) method. From the experimental results, obvious improvement of corrosion fatigue strength was observed in TiN coated specimens, as compared with those without coating. The corrosion fatigue crack propagation rate observed on the surface of coated specimens was equivalent to that without coating. Fracture surface observations with a scanning-electron microscope revealed that the corrosion fatigue crack propagated from small corrosion pits formed at the base metal under the coating layer due to aqueous solution transmitted throughout the small pinhole or flaw of the coating. The causes of the improvement in the corrosion fatigue resistance of TiN coated material were elucidated that the TiN layer does not peel off from the substrate surface owing to its enough adhesion and corrosion resistance of the layer itself is more excellent than that of the substrate metal.

Effect of preloading on corrosion fatigue of 70/30 brass

AbstractThe effects of a single tensile overload and precycling load in air on subsequent corrosion fatigue cracking in 70/30 brass exposed to 1 M sodium nitrite solution were studied. A single tensile overload caused a decrease in subsequent corrosion fatigue crack propagation rate. Precycling load also showed retardation effects, depending on the load conditions for precycling and corrosion fatigue. A transsition from a higher mean stress for precycling to a lower mean stress for corrosion fatigue decreased corrosion fatigue crack growth rate, while an opposite transition did not appreciably change the corrosion fatigue crack propagations. The responses of bulk mechanical properties to a presingle overload and precycling load in air were measured, showing hardening which may probably be responsible for the observed retardation.

Kinetics of corrosion fatigue crack propagation behaviour of Al—Zn—Mg alloy using centre notched specimens

Abstract Kinetics of corrosion fatigue (CF) crack propagation in an Al—Zn—Mg alloy have been studied as a function of applied potential and temperature in a 3·5 wt-% NaCl solution using centre notched specimens. This study especially concerned the stress corrosion (SC) crack propagation associated with CF crack propagation. CF crack propagation rate increased with increasing applied potential. CF and SC cracks both propagated in a brittle intergranular manner. CF crack propagation was thought to be an enhanced phenomenon of SC crack propagation. By modifying the simple superposition model, synergistic interaction between pure fatigue and environmental effects was taken into consideration in evaluating the CF crack propagation rate. in terms of the SC crack propagation rate. The present experimental data also led to the conclusion that the CF crack propagation rate is simply proportional to (∆Κ)2·0–2·2, and Boltzmann's factor, where ∆Κ is the stress intensity range. The apparent activation energy for CF cr...