The Damage And Life Evaluation Of Q235under The Synergy Impact Of Stress And Corrosive Media

Special equipment is widely used in the field of production and life. The materialof special equipment is not only to withstand the corrosive effect of the environment,but also withstand the high stress state of the load. Therefore, to ensure the safe use ofspecial equipment, it must be given full consideration to the materials which bothwithstand synergistic effect of stress and corrosive media, and study the damagebehavior under synergistic effect of stress and corrosive environment.The presence of the stress may impact the corrosion rate of a material. This paperdiscusses the mechanochemical effect caused by stress and corrosive media in the viewof damage mechanics combined with thermodynamics and metal electrochemical. Theresults show that in the environment the presence of stress will lower theelectrochemical bit of metal, increase the corrosion current. As a result of that the metalcorrosion speed is accelerated.There are two kinds of Q235corrosion samples, one is under load and the otherone is without load. After the acetic acid salt spray corrosion test for the two kinds ofsamples. The results show that the main corrosion morphology of low carbon steelQ235is pitting corrosion in acidic salt spray environment and there is also a slightgeneral corrosion. And the corrosion samples under stress corrode faster than thecorrosion specimens under no stress. In a word, the existence of the stress acceleratesthe corrosion of materials.The Open circuit potential、Polarization curve and AC impedance spectroscopy ofQ235under different stress levels in ASS solution also be tested. The results show thatthe existence of stress makes the corrosion potential of Q235becomes more negative,so it increases the trend of the electrochemical corrosion. At the same time, the existence of stress makes the polarization resistance of Q235become smaller whichincreases the corrosion current and accelerates the corrosion of Q235.With the test results the paper gives a brief discussion on the pitting corrosionmechanism of Q235that in salt spray environment. And it establishes the growth modelof pits and the remaining life prediction of Q235in the salt spray environment.Finally, there is a introduction for a natural gas pipeline accident that the authorparticipated in. There was serious mechanical damage on outer surface of the accidentpipeline. The mechanical damage destroyed the coating of the accident pipeline andmade the metal material directly exposed to the corrosive environment. As a result ofthat localized corrosion appeared on the mechanical damage. Because the stress at themechanical damage was larger, so the electrochemical bit was more negative and thecorrosion speed is larger. Eventually, under the synergy impact of stress and corrosivemedia the crack appeared at the mechanical damage and the pipeline exploded.