Observation of the pitting corrosion and uniform corrosion for X80 steel in 3.5 wt.% NaCl solutions using in-situ and 3-D measuring microscope

• The initiation and propagation processes of corrosion pits for X80 in NaCl solutions were observed in situ.
• Both regular pits and the corrosion products of uniform corrosion were observed simultaneously.
• Pits are mostly initiated by mechanical defects, with some of the pits initiated by metallic inclusions.
• Mechanisms related to the initiation and growth of pits and the transition into uniform corrosion are proposed.

The corrosion morphology of X80 steel in neutral NaCl solutions was investigated using an in situ 3-D measuring microscope. The time-evolutions of the initiation and propagation process of corrosion pits are presented and the three-dimensional structure of the corrosion pits could be observed. Both regular corrosion pits and corrosion products of this uniform corrosion could be analyzed. Furthermore, the effect of temperature on the corrosion morphology was studied. The mechanisms related to the initiation and propagation processes of pitting corrosion as well as the effect of temperature for X80 in NaCl solutions have been proposed.