Stress corrosion behavior of X80 pipeline steel in the natural seawater with different dissolved oxygen contents

Abstract

Stress corrosion slow strain rate tensile tests of the X80 steel in the natural seawater are carried out to study the effect of dissolved oxygen (DO) on the sensitivity of stress corrosion. Scanning electron microscope (SEM) combined with the electrochemical measurement is adopted to analyze the mechanism and affecting factor of the stress corrosion cracking (SCC). The results show that the sensitivity of SCC in the natural seawater increases and the stress corrosion cracking gradually transforms from ductile to quasi-brittle fracture, with the increase of dissolved oxygen content. Tafle polarization curves and electrochemical impedance spectroscopy of X80 steel show that the dissolved oxygen aggravates the electrochemical corrosion and reduces the corrosion resistance. The corrosion pits and micro cracks at the lateral and fracture surface trigger the stress concentration and promote the anodic dissolution under the applied stress, thereby accelerate the process of stress corrosion cracking of the X80 steel.