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RESEARCH PAPERS

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

[+] Author and Article Information
K. Kim

Department of Marine Engineering, Korea Maritime University, Pusan, Korea

W. H. Hartt

Center for Marine Materials, Department of Ocean Engineering, Florida Atlantic University, 777 Glades Road, Boca Raton, FL 33431

J. Offshore Mech. Arct. Eng 117(3), 192-199 (Aug 01, 1995) (8 pages) doi:10.1115/1.2827089 History: Received November 28, 1994; Revised March 14, 1995; Online December 17, 2007

Abstract

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.

Copyright © 1995 by The American Society of Mechanical Engineers
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