Study Of Corrosion Behavior Of Q235 And X70 Steels In BaoTou Soils

On the basis of the"West-to-East Natural Gas Transmission Project", the corrosion of Q235steel and X70 pipeline steel in Baotou field of Inner Mongolia was studied by burying specimen firstly in soils in place and Laboratory soils.After Q235steel and X70 pipeline steel were buried for one year and two years in soils in place, the corrosion of Q235steel and X70 pipeline steel was analysed by photographic process,scanning electron microscopy and energy spectum analysis, corrosion rate counted , The results show that Q235steel and X70 pipeline steel were corroded severely. The corrosion rate of the X70 pipeline steel is 0.0219g/dm~2.day for one years, 0.00501g/dm~2.day for tow years;The corrosion rate of Q235 steel is 0.01794g/dm~2.day for one years,0.00368g/dm~2.day for tow years. X70 steel's inclination to pitting corrosion was stronger than Q235 steel's. The corrosion products of Q235steel and X70 pipeline steel contain oxidates and sulfides of iron.The Q235steel and X70 pipeline steel were buried in Laboratory soils. The moisture content of solids were 5%,10%,15% and 20% at 15℃,and the temperature of solids were 15℃,30℃and 45℃in solids of 15%.By natural corrosion potential measured,EIS and polarization curve, the test samples were analysed by scanning electron microscopy ,energy spectum analysis and X-ray powder diffraction apparatus. The results show that corrosion of Q235steel and X70 pipeline steel were non-uniform general corrosion.The sifference of the corrosion rate of X70 pipline steel and Q235 steel was very little. The corrosion products of Q235steel and X70 pipeline steel were oxidates of iron. The resistance of electrochemical reaction is increases with reducing of dampness and temperature and elongation of time.The corrosion behavior of Q235 steel and X70 pipeline stee were contrasted in soils of in place and Laboratory soils. The reaction of the Q235steel and X70 pipeline steel corroded is depolarization of oxygen and sulfate soils in place of Baotou. The corrosion rate of the Q235 steel and X70 pipeline steel increases early and decreases later with increase of moisture cintent of Baotou soils. The corrosion rate of the Q235 steel and X70 pipeline steel was maximum in soils of moisture content 15%. The corrosion rate of the Q235 steel and X70 pipeline steel exceed 20 g/dm~2·a for 50 day in the soils of moisture content 10% and of 45℃.