Fatigue-Crack Growth in an X-65 Line-Pipe Steel at Low Cyclic Frequencies in Aqueous Environments

Abstract

The effects of salt and distilled water environments on fatigue-crack growth rales have been evaluated for an X-65 line-pipe steel. Tests were conducted over a frequency range between 10 and O.Ol Hz, under conditions of cathodic potential and free corrosion. A distinct pattern in the functional dependence of growth rates on AK and frequency has been found. Maximum environmental enhancement of growth rates was SO times that of air at a cathodic potential of ~1.04V, and 10 times that of air at a free-corrosion potential of -0.68V. In each case it occurred at Die lowest frequency and at relatively high values of AK. Hydrogen embrittlement and the two-stage cracking process are examined as the main mechanisms of growth acceleration.Transactions of the ASME Downloaded From: http://materialstechnology.asmedigitalcollection.asme.org/ on 05/31/2015 Terms of Use: http://asme.org/terms Transactions of the ASME Downloaded From: http://materialstechnology.asmedigitalcollection.asme.org/ on 05/31/2015 Terms of Use: http://asme.org/terms

Ermüdungsfestigkeit

“…[1363] schlagen Wei u. Simmons [1366] vor, die Anteile der rein mechanischen Ermüdung, der eigentlichen Korrosionsermüdung und der Spannungsrißkorrosion zur Rißfortschrittsrate aufzusummieren. 6.69 (a)).…”

Fractographic Analysis in the Understanding of Corrosion Fatigue Mechanisms

“…This lack of a threshold is observed in the work of Vosikovsky [13], in which hydrogen assisted growth dominates due to the application of a cathodic potential.…”

A relative crack opening time correlation for corrosion fatigue crack growth in offshore structures

“…For example, in the work of Thorpe et al , it was found that crack growth rates in BS4360 50D steel in seawater were significantly enhanced at a lower frequency, but at a higher frequency, crack growth rates were found to be similar to those measured in an air environment. A similar phenomenon was also reported by Vosikovsky for X65 pipeline steel tested in 3.5% salt water . A higher load frequency was also reported to have negligible effects on crack growth rates in 12Ni‐5Cr‐3Mo maraging steel tested in 3% sodium chloride solution .…”