Evaluation of Long-Term Corrosion Fatigue Life of Ship and Offshore Structural Steel

Abstract

In this study, an evaluation of the long-term corrosion fatigue life of ships and offshore structural carbon steel was conducted, and the result is compared with data from other experimental studies. The evaluation was carried out as follows:

• 1) First, an evaluation of the increased stress, caused by general corrosion, was conducted to calculate the crack initiation life and propagation life. This stress increase, due to area reduction from the weight loss, was calculated through an evaluation of the corrosion rate obtained from 16 years of published weight loss data from continuous immersion in seawater.

• 2) Second, an evaluation of the moment of crack initiation (Ni), when a crack is initiated at the corrosion pit, was conducted. The depth of the corrosion pit was calculated from 16 years of continuous immersion test data of pit penetration.

To determine the instant of crack initiation at the corrosion pit, the Komai threshold value for crack initiation at the corrosion pits was adopted. To calculate the stress intensity factor of a crack, the Newman-Raju formula was used.

• 3) Finally, the crack propagation life was evaluated from crack initiation to fracture. The results of the evaluation are compared with long-term S-N experimental corrosion fatigue test data.

In this study, the long-term corrosion fatigue life estimation method, using weight loss and pit corrosion data by long-term immersion corrosion data, was investigated. The evaluation results were found to reflect the tendency of long-term S-N fatigue test results.