A New Parameter for Characterizing Corrosion Fatigue Crack Growth

1981 ◽  
Vol 103 (4) ◽  
pp. 298-304 ◽  
Author(s):  
T. Shoji ◽  
H. Takahashi ◽  
M. Suzuki ◽  
T. Kondo
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Corrosion Fatigue ◽  
Crack Tip ◽  
Corrosion Fatigue Crack ◽  
Mechanical Factors ◽  
Corrosion Fatigue Crack Growth

The role of mechanical factors, such as ΔK, R, and K˙ (loading rate), and its significance on corrosion fatigue crack growth acceleration were discussed in terms of crack tip strain rate and/or nucleation rate of fresh metal surface. A new parameter for characterizing corrosion fatigue crack growth was proposed, paying attention to rates of crack tip mechanochemical reactions, i.e., oxide film rupture rate, passivation rate, and solution renewal rate, which are influenced by the crack tip mechanical condition, microstructure of material, and environment. Hence a new parameter da/dt]air, the time base pure fatigue crack growth rate which was related closely to crack tip deformation rate, was introduced as a measure of actual crack tip strain rate. In various combinations of materials and environments, it was shown that the value of da/dt]air determines a crack growth rate in the environment, irrespective of mechanical factors such as ΔK, Kmax, R, and K˙, or frequency.

scholarly journals Effect of Various Factors Produced by Welding on the Corrosion Fatigue Crack Growth Rate

1987 ◽  
Vol 36 (12) ◽  
pp. 774-780
Author(s):  
Toshio Terasaki ◽  
Tetsuya Akiyama ◽  
Masatoshi Eto ◽  
Yasuhumi Matsuo ◽  
Masaharu Kusuhara
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Corrosion Fatigue ◽  
Corrosion Fatigue Crack ◽  
Corrosion Fatigue Crack Growth

Effect of Hold-Time Interspersed With Cyclic Loading on Corrosion Fatigue Crack Growth Rate of a Steel in Sodium Chloride Solution

2018 ◽  
Author(s):  
Raghu V. Prakash ◽  
Dhinakaran Sampath
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Corrosion Fatigue ◽  
Hold Time ◽  
Corrosion Fatigue Crack ◽  
Corrosion Fatigue Crack Growth

Corrosion fatigue growth behavior of structural steels at low cyclic frequency is characterized by an increase in crack growth rate in the threshold and Paris regions, due to the simultaneous action of cyclic mechanical load (fatigue) and corrosive environment. Knowledge on the effect of load sequence on corrosion fatigue crack growth is important to set out the realistic design and prognosis criteria for components operating under corrosive environments. In this study, the corrosion fatigue crack growth rate under the effect of hold-time (1000s), at a maximum stress intensity factor (Kmax), interspersed during cyclic load on was studied experimentally on a Mn-Ni-Cr steel under 3.5% NaCl solution at a constant stress intensity factor range (ΔK) of 15 MPa √m; the corrosion crack growth rate was evaluated for three different frequencies of: 0.01, 0.1 and 1 Hz. As a result of hold time at the peak load, the exposure time for the crack-tip to interact with the environment increased, which could enhance the corrosion crack growth rates. To verify if this corrosion effect can be contained, electrode potential of (−) 850 mV and (−) 950 mV SCE was applied to the specimen to reduce the extent of corrosion contribution to crack growth rate. The fatigue crack growth rate (da/dN) increased when the frequency was decreased from 1 to 0.01 Hz at all electrode potentials. However, the crack growth rate at 0.01 Hz increased by an order of magnitude with a tensile hold at Kmax for 1000 s compared with the crack growth rate during continuous cyclic load for a given electrode potential. The crack growth rate reduced when the electrode potential was decreased to −950 mV SCE. The enhancement of corrosion fatigue crack growth rate with the introduction of a hold-time is explained using crack-tip strain rate assisted anodic dissolution.

Role of Crack Closure in Crack-Size-Dependent Corrosion-Fatigue Crack Growth of X65 Steel Exposed to Sour Brine Environment

2018 ◽  
Author(s):  
Baotong Lu ◽  
Stephen J. Hudak ◽  
Carl F. Popelar
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Corrosion Fatigue ◽  
Phase 1 ◽  
Crack Size ◽  
Corrosion Fatigue Crack ◽  
Corrosion Fatigue Crack Growth

Corrosion-fatigue in sour brine (SB) environments is a significant design consideration in deepwater floating production systems. Extensive testing over the past 20 years has shown that sour brine environments can reduce the fatigue life of line pipe steels by factors of 10× to 50× compared to fatigue lives measured in laboratory air; moreover, the extent of material degradation depends on a multitude of loading, environmental, and materials variables. Thus, in 2010 Southwest Research Institute (SwRI) embarked on an industry-supported Joint Industry Project (JIP) to develop a quantitative model to predict the effects of these variables on corrosion-fatigue crack growth rate (CFCGR) in offshore structure steels exposed to sour brine environments. Phase 1 of this JIP had successfully developed and validated such a model in the intermediate fatigue crack growth rate regime — i.e., with CFCGRs between 10−4 ∼ 10−2 mm/cycle. However, the Phase 1 model gave overly conservative CFCGRs at rates in the low growth rate regime below 1 × 10−4 mm/cycle, corresponding to S-N corrosion-fatigue lives in the high-cycle fatigue regime. It was hypothesized that these conservative predictions might result from the fact that the model did not consider effects of crack closure that could significantly reduce the effective crack-driving force in this low growth rate regime, a process that might also give rise to crack-size effects. Thus, the primary objective of the current study was to assess whether or not crack closure is responsible for the conservativism in the Phase 1 CFCGR model, as well as to explore related crack-size effects that in theory would not be predictable with conventional linear elastic fracture mechanics. Both of these possible effects are explored here using critical CFCGR experiments on X65 steel in sour brine under loading conditions for which the nominally applied mechanical driving force (ΔK), as well as the stress ratio (Rσ) and loading frequency were held constant, while crack closure measurements were made as the crack grew from 2 mm to about 10 mm. The crack closure measurements were made using elastic compliance measurements made with a specially designed, high-sensitivity clip gage. Results indicate that a crack-size dependence of CFCGR did occur and could be correlated using a crack-closure-corrected effective stress intensity factor (ΔKeff). These results have provided a foundation for extending the JIP’s Phase 1 CFCGR model into the low growth rate regime in the ongoing Phase 2 of the JIP.

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