Abstract
Slow strain rate stress corrosion test of X80 steel in the natural seawater are carried out to study to effect of dissolved oxygen on the sensitivity of stress corrosion. Scanning electron microscope (SEM) combined electrochemical measurement are adopted to analyze mechanism and the influencing factor of stress corrosion cracking. 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. Tafle polarization and electrochemical impedance spectroscopy of X80 show that dissolved oxygen aggravates electrochemical corrosion and reduces corrosion resistance. Corrosion pits and micro cracks at the lateral and fracture surface trigger stress concentration and promote anodic dissolution under stress, thereby accelerate the process of stress corrosion cracking of X80 steel in the seawater.
Highlights
S ubmarine pipeline is an indispensable part and the lifeline of offshore oil-gas exploitation
The stress-strain curves of the X80 specimens measured in the seawater with different dissolved oxygen (DO) contents are shown in Fig. 3, and the stress-strain curve in air is depicted for comparison
The tensile strength and elongation of X80 steel in seawater are obviously lower than that in air, and this decline increase with the increasing DO, indicating that X80 steel has a strong susceptibility of Stress corrosion cracking (SCC) to the DO in the seawater
Summary
S ubmarine pipeline is an indispensable part and the lifeline of offshore oil-gas exploitation. According to the pH value of the service environment, SCC of the pipelines steel can be divided into high, near neutral and low pH types. The stress corrosion mechanism of pipeline steel in a near neutral environment has been widely accepted as the interaction of anodic dissolution and hydrogen embrittlement. A number of studies have been performed to investigate the corrosion behavior of pipeline steel in the natural marine environment [13,14,15]. Research work on the stress corrosion behavior of X80 pipeline steel in the natural seawater is very limited. A model that stress concentration promotes the anodic dissolution and the SCC fracture is adopted to explain this accelerating effect once the corrosion pits and microcracks are formed
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