• Journal of Ocean Engineering and Technology
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• v.11 no.2
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• pp.28-38
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• 1997

The corrosion fatigue test was conducted in air to investigate the corrosion fatigue strength of SM 30 C steel by which was corroded in the under sea and surface in the conditions of 3.0% NaCl salt solution. The fatigue tests were carried out on a rotary bending testing machine of cantilever type. The corrosion effect of the sea surface conditionwas served more than that of the under sea condition which was due ti the periodic contact of air thus accelerate the corrosion. The difference of the fatgue strength between sea surface and under sea conditions decreased with increase of stree level and corroded period. Inthe case of the solid shaft and thickness 2mm of hollow shaft, the difference of corrosion fatigue strength decreased as stress level and corrosion periodic increasing. Onthe contrary in the case of thickness 1mm of hollow sgaft, the difference of it increased as stress level, corrosionn periooodic increasing and also the condition of corrosion chaanged. The main factors affecting the degradation of fatigue strength due to corrosion were the reduction of sectional area and the increase of surface roughness. The interference phenomenon increase with stress level got higher.

• Nuclear Engineering and Technology
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• v.53 no.1
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• pp.304-313
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• 2021

Nickel base Alloy X-750, which is used as fastener parts in light-water reactor (LWR), has experienced many failures by environmentally assisted cracking (EAC). In order to improve the reliability of passive components for nuclear power plants (NPP's), it is necessary to study the failure mechanism and to predict crack growth behavior by developing a probabilistic failure model. In this study, The Bayesian inference was employed to reduce the uncertainties contained in EAC modeling parameters that have been established from experiments with Alloy X-750. Corrosion fatigue crack growth rate model (FCGR) was developed by fitting into Paris' Law of measured data from the several fatigue tests conducted either in constant load or constant ΔK mode. These parameters characterizing the corrosion fatigue crack growth behavior of X-750 were successfully updated to reduce the uncertainty in the model by using the Bayesian inference method. It is demonstrated that probabilistic failure models for passive components can be developed by updating a laboratory model with field-inspection data, when crack growth rates (CGRs) are low and multiple inspections can be made prior to the component failure.

• Journal of the Korean Society of Safety
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• v.14 no.2
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• pp.3-10
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• 1999

Fatigue crack growth rates in commercial plate of high strength Al 7075-T651 were investigated for the T-L direction in air, water and sea water. In this paper the effect of cyclic load wave-form(trapezoid and triangle) on fatigue crack growth rates in air, water and sea water environments were investigated using standard LEFM testing procedures. It was founded that the fatigue crack growth behaviors were not affected by cyclic load wave-forms. In region II (stable crack growth region), the fatigue crack growth behaviors were insensitive to cyclic load wave-forms and were sensitive to environment i.e. fatigue crack growth behaviors were higher in sea water than in air for all cyclic load wave-form. The result of fractographical morphology in air, water and sea water by SEM showed obvious dimple rupture and typical striation in air, but transgranular fracture surface in water and sea water. The values m are not affected by corrosion environments but C are different values.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.3 s.174
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• pp.603-612
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• 2000

Corrosion characteristics on the 12Cr alloy steel of turbine blade was electro-chemically investigated in 3.5wt% NaCI and 12.7wt% Na2S04 solution, respectively. Electro-chemical polarization test, Huey test and Oxalic acid etching test were previously conducted to estimate corrosion susceptibility of the material. And, using the horizontal corrosion fatigue tester, corrosion fatigue characteristics of 12Cr alloy steel in distilled water, 3.5wt% NaCI solution, and 12.7wt%(1M) Na2S04 solution were also fracture-mechanically estimated and compared their results. Parameter considered was room temperature, 60'C and 90'C. Corrosion fatigue crack length was measured by DC potential difference method.Obtained results are as follows,1) 12Cr alloy steel showed high corrosion rate in 3.5wt% NaCI solution and Na2S04 solution at high tempratue.2) Intergranular corrosion sensitivity of 12 Cr alloy was smaller than austenitic stainless steel.3) Corrosion fatigue crack growth rate in 3.5wt% NaCI and 12.7wt%(IM) Na2S04 solution is entirely higher than in the distilled water, and also increased with the temperature increase.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.5
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• pp.181-187
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• 2000

Fatigue tests under acid fog environment were carried out to investigate the effect of acid fog on the corrosion fatigue strength of SM55C in comparison with distilled water. Main results obtained are as follows. The fatigue strength of SM55C under acid fog environment are remarkably decreased as compared with that of distilled water specimen. The corrosive effect of acid fog on fatigue strength are more serious under low stress amplitude level than under high stress amplitude level, and this leads to continuous reduction of fatigue strength. Under acid fog environment in early stage of crack growth. because the corrosive components dissolve the crack face offensively. the unstable fracture surface appears. But, the stable corrosion precipitation and products layer are formed on the fracture surface in accordance with the time pass.

• Journal of Ocean Engineering and Technology
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• v.1 no.1
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• pp.111-119
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• 1987

The corrosion fatigue crack propagation characteristics of SS41 steel in 3.5% NaCl solution have been evaluated for loading frequencies of 1Hz and 0.2Hz. A sine wave loading profile was used for fatigue testing. Each test was carried out at a constant stress ratio, R(0.1). The main results are summarized as follows; 1. Fatigue crack propagation rate was higher in 3.5% NaCl solution than in air, higher in the base metal than in the weld metal, and higher at f =0.2Hz than at f =1Hz. 2. The crack closure level of the base metal was not influenced by cyclic frequencies, but that of the weld metal was much influenced. 3. When the crack closure effect was eliminated in the evaluation of crack propagation characteristics by using $\Delta K_{eff}$, the envirommental influence was distinctly observed. At the base metal, crack propagation rate was enhanced by the hydrogen embrittlement, and the weld metal was reduced by the crac closure. 4. There was clearly observed hydrogen embrittlement and severely corroded aspect at fracture surface of lower frequency than that of higher frequency, and at that of base metal than that of the weld metal.

• Journal of the Korean Society of Safety
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• v.13 no.4
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• pp.113-120
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• 1998

Fatigue crack growth rates(i.e. crack initiation and crack growth of short and long crack) are investigated using commercial plates of high strength Al alloy 7075-T651 for the transverse-longitudinal(T-L) direction in air, water and sea water. Also, the evaluation direct current potential drop(D.C.P.D) method and the fractographical analysis by SEM are carried out. Near threshold region, short crack growth rates were much faster than those of comparable long cracks, and these short crack growth rates actually decrease with increasing crack growth and eventually merge with long crack data. Fatigue crack propagation rates in aggressive media(i.e. sea water) increase noticeably over three times those in air. One of the most significant characters in this phenomenon as a corrosion-fatigue causes an acceleration in crack growth rates. Sea water environment, particularly Cl$^{[-10]}$ solution brings the most detrimental effects to aluminum alloy. The result of fractographical morphology in air, water and sea water by SEM shows obvious dimpled rupture and typical striation in air, but transgranular fracture surface in water and sea water.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.6
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• pp.2465-2471
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• 2012

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-${\Delta}K$ were obtained. At this test, when ${\Delta}K$ is low, the crack propagation rates were accelerated compared to those of seawater condition, however, when ${\Delta}K$ 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.

• Journal of Ocean Engineering and Technology
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• v.7 no.2
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• pp.131-140
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• 1993

To study the corrosion fatigue begavior of T.M.C.P. steel, the rotary bending fatigue test with the change of concentration of NaCl solution was carried out. Fatigue life in the corrosion environment is decreased markedly in comparision with that in the air. Fatigue limit in the air was about 225 MPa. In case of 3.5% NaCl solution fatigue life could be expressed as .sigma./sub f/=10,392 * (N/sub f/)/sup -o.2923 . According to the paris's rule, crack growth rates could be expressed as da/dN=2.62.*10/sup -7/ .DELTA. K/sup 1.09/(3.5% NaCl solution), da/dN=1.95 *10/sup -7 .DELTA. K/sup 1.05/(1% NaCl solution), da/dN=2.62 * 10/sup -7/.DELTA./sup 0.72/(0.01% NaCl solution) with da/dN expressed in mm/cycle and .DELTA.K in MPa.GAMMA.m. The crack growth rate in the corrosion environment was highest under 3.5% NaCl solution.

• Journal of Fisheries and Marine Sciences Education
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• v.9 no.2
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• pp.198-208
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• 1997

Recently, with rapid increase of gas demand, there occurs much interest their security of safety in the gas storage tanks and pressure vessels etc. In order to solve the problems, the occurrence of corrosion fatigue crack and the propagation behavior must be investigated. Especially the occurrence of corrosion fatigue crack and the propagation behavior in the part which has concentrated stress or defects, must be studied more carefully. In this paper, the high-tensile steel of SPV 50 which is much used for building the LPG storage tanks was tested by the use of a plane bending corrosion fatigue tester under the various marine environment and in the air. These experiments were carried out to investigate the surface crack propagation behavior, the value of experimental constant for Paris' rule(da/dN=$C(K)^m$), the crack depth propagation rate and the accelerative factor of the surface crack propagation rate. The main results obtained are as follows ; 1) As the specific resistances of marine environment decreases, the exponential value of slope m of Paris' rule(da/dN=$C(K)^m$) decreases and the value of intercept C increases. 2) The surface crack propagation rate and the crack depth propagation rate are delayed, as the specific resistances of marine environment is increased. 3) The accelerative factor of the surface crack propagation rate by corrosion fatigue is higher, according as the stress intensity factor range ${\Delta}K_A$ is small.