Corrosion Fatigue Testing of Steels as Applicable to Offshore Structures

This paper reports substantially enhanced fatigue and corrosion-fatigue lifetimes of propulsion shaft materials, 23284A steel and 23284A steel with In625 weld overlay cladding, as a result of shot or laser peening. Glass reinforced plastic (GRP) coatings and Inconel claddings are used to protect shafts against general corrosion and corrosion pitting. However salt water leakage penetrating under a GRP can actually enhance pitting leading to crack initiation and growth. Fatigue coupons, untreated and with shot or laser peening were tested, including with simultaneous salt water immersion. Controlled corrosion of the surfaces was simulated with electric discharge machining (EDM) of deep pits enabling evaluation of fatigue and corrosion-fatigue lifetimes. Results specifically show high energy laser peening (HELP) to be a superior solution, improving corrosion-fatigue resistance of shaft and cladding metal, reducing the potential for corrosion pits to initiate fatigue cracks and dramatically slowing crack growth rates. At a heavy loading of 110% of the 23284A steel yield stress and with 0.020 inch deep pits, laser peening increased fatigue life of the steel by 1370% and by 350% in the corrosion-fatigue testing.

Download Full-text

Time Series Simulations of Wide-Band Spectra for Fatigue Tests of Offshore Structures

Journal of Energy Resources Technology ◽

10.1115/1.3231107 ◽

1984 ◽

Vol 106 (4) ◽

pp. 466-470 ◽

Cited By ~ 8

Author(s):

N. K. Lin ◽

W. H. Hartt

Keyword(s):

Time Series ◽

Fatigue Testing ◽

Wide Band ◽

Simulation Method ◽

Offshore Structures ◽

Fatigue Tests ◽

Time Series Model ◽

Long Time ◽

Band Spectra ◽

Time Series Simulation

A time-series simulation method, based on the principle of time series modeling for dynamic systems, is used to reproduce a wide-band stress history from a prescribed stress spectral model for fatigue testing of offshore structures. The optimization procedures and stability of the time series model for the prescribed spectrum are presented and discussed. The optimization procedures are developed on the basis of the Levison-Durbin algorithm, which usually produces a stable time series model if the order of the time series model is even. An example is presented to demonstrate the applicability of the proposed method to long-time, high-cycle fatigue testing.

Download Full-text