Response of Short Cracks in High-Strength Steels to Fatigue Loadings—Part II: Behavior in Seawater Under Cathodic Polarization

1995 ◽  
Vol 117 (3) ◽  
pp. 192-199 ◽  
Author(s):  
K. Kim ◽  
W. H. Hartt
Keyword(s):  
Crack Growth ◽  
Cathodic Polarization ◽  
High Strength Steels ◽  
High Strength ◽  
Potential Drop ◽  
Offshore Structures ◽  
Natural Seawater ◽  
Short Cracks ◽  
Test Parameters ◽  
Point Bend

Experiments have been performed to determine the fatigue crack growth rate (FCGR) of short cracks (length from 0.1 to several mm) of five steels with yield stress in the range 370–570 MPa while cathodically polarized in natural seawater. Attention was focused on regions I and II of the classical FCGR-stress intensity range curve with particular consideration being given to the near-threshold behavior of short cracks. Single-edge notched, three-point bend specimens and a direct current potential drop crack monitoring system were employed; and test parameters were selected to simulate conditions experienced by deepwater offshore structures. These included a stress ratio of 0.5, a frequency of 0.3 Hz, and three levels of cathodic polarization (−800,−950, and −1100 mV, SCE). Crack growth rates were evaluated in terms of environment (air versus seawater), potential, material, and crack length. It was determined that cathodic polarization was generally beneficial with regard to FCGR compared to the freely corroding case, even at the most negative potential considered (−1100 mV, SCE), in contrast to what occurs for macro-cracks. The results are discussed within the context of design of offshore structures for resistance to fatigue.

Response of Short Cracks in High-Strength Steels to Fatigue Loadings—Part I: Behavior in Air and Freely Corroding in Seawater

1995 ◽  
Vol 117 (3) ◽  
pp. 183-191 ◽  
Author(s):  
K. Kim ◽  
W. H. Hartt
Keyword(s):  
Growth Rate ◽  
Crack Growth ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
High Strength Steels ◽  
High Strength ◽  
Natural Seawater ◽  
Offshore Structure ◽  
Short Cracks ◽  
Test Conditions

Experiments have been performed which determined the growth rate of short cracks (initial depth ~ 0.1 mm) for five high-strength steels (yield stress 370–570 MPa) in air and natural seawater. Attention was focused on regions I and II of the classical da/dN-ΔK curve with test conditions being relevant to offshore structure service. The results indicated enhanced growth rate for short fatigue cracks (a ⪝ 1 mm) in both environments. Parameters with which short crack fatigue behavior might best be correlated were investigated, and it was found that the enhanced fatigue crack growth rate associated with short cracks transitioned to long crack growth kinetics at a ΔK value which depended only upon environment. The significance of the results are discussed within the context of offshore structure integrity.

Mechanistic Features of Short Fatigue Crack Growth Kinetics for High Strength Steels in Sea Water

2004 ◽  
Vol 128 (2) ◽  
pp. 169-176 ◽  
Author(s):  
Kijoon Kim ◽  
William H. Hartt
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Kinetics ◽  
High Strength Steels ◽  
High Strength ◽  
Offshore Structures ◽  
Rate Kinetics

The importance of fatigue to the integrity of offshore structures is well documented. Also, it has been demonstrated that much of the service life of members and components such as tendons and risers is comprised of an extension of cracks from initial surface defects to a size of several millimeters. At the same time, the growth kinetics of such short cracks has been shown to be more rapid than those of long cracks; however, it is upon the latter that most historical studies have focused. In the present paper, the results of scanning electron microscope fractographic analyses performed upon five high strength steels fatigued in air and seawater are presented. These revealed fracture surface morphology distinctions that were a unique function of material, environment (air versus seawater), potential, and crack length, and that the enhanced fatigue crack growth rate in the short crack regime was relatable to these morphological features. Of particular importance were (1) the development of secondary cracks as a precursor for the short crack to long crack growth rate kinetics transition, and (2) a change in fracture mode, either from quasicleavage (QC) to microvoid coalescence (MVC) or from intergranular to QC or MVC with increasing crack length. The results are discussed within the context of (1) alloy development for applications where a significant portion of the fatigue life transpires while cracks are relatively short such that the enhanced growth rate kinetics apply; and (2) materials selection and fatigue design of riser and tendon systems for deep water offshore structures.

scholarly journals Scanning Kelvin Probe Investigation of High-Strength Steel Surface after Impact of Hydrogen and Tensile Strain

2020 ◽  
Vol 1 (1) ◽  
pp. 187-197 ◽  
Author(s):  
Andrei Nazarov ◽  
Flavien Vucko ◽  
Dominique Thierry
Keyword(s):  
Tensile Deformation ◽  
Electron Work Function ◽  
High Strength Steels ◽  
High Strength ◽  
Potential Drop ◽  
Hydrogen Uptake ◽  
Surface Oxide ◽  
Kelvin Probe ◽  
Scanning Kelvin Probe ◽  
Cracking Mechanisms

Hydrogen in combination with mechanical stress can lead to rapid degradation of high-strength steels through environmentally assisted cracking mechanisms. The scanning Kelvin probe (SKP) was applied to automotive martensitic steel grade MS1500 in order to detect local reactivity of the surface after hydrogen uptake and tensile deformation. Hydrogen and stress distribution in microstructures can be characterized by SKP indirectly measuring the potential drop in the surface oxide. Thus, the links between electron work function, oxide condition, and subsurface accumulation of hydrogen and stress have to be investigated. It was shown that plastic strain can mechanically break down the oxide film creating active (low potential) locations. Hydrogen effusion from the steel bulk, after cathodic charging in aqueous electrolyte, reduced the surface oxide and also decreased potential. It was shown that surface re-oxidation was delayed as a function of the current density and duration of cathodic hydrogen pre-charging. Thus, potential evolution during exposure in air can characterize the relative amount of subsurface hydrogen. SKP mapping of martensitic microstructure with locally developed residual stress and accumulated hydrogen displayed the lowest potential.

Fatigue Crack Propagation Limit Curves for S690QL and S960M High Strength Steels and their Welded Joints

2018 ◽  
Vol 1146 ◽  
pp. 44-56 ◽  
Author(s):  
János Lukács ◽  
Ádám Dobosy ◽  
Marcell Gáspár
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Welded Joints ◽  
High Strength Steels ◽  
High Strength ◽  
Base Materials ◽  
Propagation Limit

The objective of the paper is to present the newest results of our complex research work. In order to determination and comparison of the fatigue resistance, fatigue crack growth tests were performed on different grades of S690QL quenched and tempered, and S960TM thermomechanically rolled high strength steels.15 mmand30 mmthick base materials were used for our investigations. Welded joints were made from these base materials, using gas metal arc welding with matching, overmatching, and undermatching filler metals. In the paper, the performance of the welding experiments will be presented, especially with the difficulties of the filler material selection; along with the results of the fatigue crack growth examinations executed on the base materials and its welded joints. Statistical aspects were applied both for the presenting of the possible locations of the cracks in the base materials and the welded joints and for the processing of the measured data. Furthermore, the results will be compared with each other, and the possibility of derivation of fatigue crack propagation limit curves will be referred.

Fatigue Crack Propagation Limit Curves for High Strength Steels and their Application for Engineering Critical Assessment Calculations

2014 ◽  
Vol 891-892 ◽  
pp. 563-568 ◽  
Author(s):  
János Lukács ◽  
Marcell Gaspar
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Welded Joints ◽  
Research Work ◽  
High Strength Steels ◽  
High Strength ◽  
Critical Assessment ◽  
Propagation Limit

There are different prescriptions containing fatigue crack propagation limit curves and rules for the prediction of the crack growth. The research work aimed (i) to determine fatigue crack propagation limit curves for high strength steels and their welded joints, based on the Paris-Erdogan law; (ii) to use the determined limit curves for engineering critical assessment (ECA) calculations. Experiments were performed on different high strength steels and their welded joints; and the propagating cracks in the specimens represent the different possible locations of the real cracks in the structural elements. Fatigue crack growth tests were executed byΔK-decreasing and constant load amplitude methods. The evaluation process consists of six steps, and by means of the selected values a statistical method can be proposed for determination of the limit curves. Engineering critical assessment calculations were performed on a welded structural element having crack like defects.

Hydrogen cracking of high-strength steels during cathodic polarization in acid media

1974 ◽  
Vol 7 (6) ◽  
pp. 683-685
Author(s):  
F. F. Azhogin ◽  
E. V. Plaskeev ◽  
O. A. Gubenkova
Keyword(s):  
Cathodic Polarization ◽  
High Strength Steels ◽  
High Strength ◽  
Hydrogen Cracking ◽  
Acid Media
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