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Taking the X80 steel used in the second West-East Pipeline Project (WEPP II) as a study object, this paper researched the effects of Cl- and SO42- with different concentration(wt% ) on internal corrosion behavior of X80 pipeline steel in stimulated solution for pigging product, discussed the nternal corrosion mechanism of WEPP II by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) experimental. The results showed that, in the stimulated solution only conaining different Cl- mass fraction, the polarization curves of X80 pipeline steel have typical characterstics of active dissolution, the corrosion current density(icorr) and the internal corrosion rate of X80 teel increases along with the increase of Cl- mass fraction; in the stimulated solution containing both 0. 05% Cl- and different SO42- mass fraction, the polarization curves of X80 pipeline steel also have typical characteristics of active dissolution, but the internal corrosion rate firstly increases and then decreases with the increase of SO42- mass fraction. When the mass fraction of SO42- is 0.50%, the icorr reaches the maximum value while polarization resistance reaches the minimum value, and the corrosion behavior of X80 steel is the most serious at this time; when the stimulated solution contain both Cl- and SO42-, the corrosion potential of X80 steel decreases while the icorr increases than the stimulated solution only containing Cl-, with the increase of SO42- mass fraction; when the stimulated solution contain both Cl- and SO42-, with the increase of SO42- mass fraction, SO42- can adsorb on he metal surface faster than Cl-, which decreases the corrosion aroused by Cl-. [ABSTRACT FROM AUTHOR]