Pitting corrosion is one of the major damage forms for Alloy 690, which is one of the usual used materials in SG tubing. It is very important to understand corrosion behavior deeply to ensure the structural integrity. In this paper, the electrochemical experiments are used to analyze the corrosion characters of Alloy 690. The results show that the corrosion rate is nearly to 0.00948 mm/a at 25 ºC, 0.01 mol·L -1 NaCl+0 mg·L -1 O 2 . The repair of the pitting is easy when the oxygen content is relatively high. Chloride ions in the solution have a certain impact on the repair potential and great influence on the pitting initiation potential. The pitting initiation potentials change from 0.64 V to 0.50 V then to 0.37 V (referring to SCE) when the content of Chloride ions increases from 0 mol/L to 0.001 mol/L to 0.01 mol/L. The competition between repair and breakdown will lead to the result of the peaks current. The repair of oxide film becomes more difficult under high potential. The difference value between pitting initiation potential and repair potential are -44.1 mV，0.0 mV，186.0 mV and 245.2 mV, respectively, when C Cl-equal to 0 mol·L -1 , 0.001 mol·L -1 , C Cl-=0.005 mol·L -1 and C Cl-=0.05 mol·L -1 . The above conclusions are important for recognizing the corrosion mechanism of Alloy 690.

The influence of deformation on electrochemical properties of Q235 steel is studied. The uni-axial tension of the steel is conducted on universal testing machine to get a series of strain, 0.07%, 6%, 11% and 24%, respectively. The deformation process for strain of 0.07% is controlled by load, and the others are controlled by displacement correspondingly. Afterward, the tests of potentiodynamic polarization and electrochemical impedance spectroscopy are conducted for the deformed steel in 0.01 mol.dm−3 NaCl solution. The results showed that plastic deformation leads to crystalline grains refine and elongate, and crystalline boundary increases, it induces more corrosive possibility and lower corrosive resistance; the corrosion potential of Q235 steel becomes more negative with the increase of deformation amount, and the corrosion current density increases with the amount of deformation; the corrosion resistance decrease with the increase of deformation seriously.