| Microbially Influenced Corrosion (MIC) is the main cause of materials service failure, and it is also the common problem in industry. The magnetic field (MF) treatment is widely applied in industry, agriculture, medical, oil and water treatment industries, the magnetic field can significantly affect the metal corrosion process. However, the effect of MF on MIC has not been paied attention. In this study, the effect of static magnetic field on sulfate reducing bacteria (SRB) influenced MIC behavior was investigated by using the electrochemical noise (EN) and surface analysis technology.1) Effec on MF on SRB growth and SRB bio film:4mT low intensity MF greatly inhibited the growth of planktonic SRB by4orders of magnitude; both4mT MF and150mT medium intensity MF delayed the decline of SRB population. Although4mT and150mT delayed the formation of sessile SRB, they both accelerated the growth rate of sessile SRB. In addition, short time MF treatment can quickly strip the formed SRB biofilm on the metal surface,4mT exhibited better performance than150mT. MF not only can change the chemical composition of the corrosion products during the corrosion process, but also can quickly change the formed corrosion products from iron sulfides to iron oxides. The final H2S concentration in the presence of MF was800μmol/L, which is much more than20umol/L in the control without MF.2) Effect of MF on diamagnetism304SS and paramagnetism Q235MIC:By using the wavelte to analyse the EN data, we can classify the corrosion process, and qualify the intensity of each corrosion type, and therefore real time study MIC. In the control condition without MF, active dissolution accured to304SS, and then metastable corrosion happened. The metastable corrosion changed into stable corrosion when the biofilm entered the log phase. The corrosion was inhibited during the decline phase. However, the304SS was passivated during the whole period in the presence of4mT MF, coupled with slightly metastable corrosion. This indicated that4mT can effectively protect304SS, mainly ascribed to the outstanding inhibition effect of4mT on SRB growth. Besides,150mT accelerated the corrosion of304SS. The metastable corrosion was mainly the corrosion type in the beginning, stable corrosion gradually appeared. Metastalbe and stable corrosion happened simultaneously during the biofilm decline phase. In addition, both4mT MF and150mT MF accelated the corrosion of Q235; the higher intensiy the severer corrosion. In the control condition, general corrosion dominated on Q235; local corrosion gradually appeared due to the accumulation of SRB biofilm. In the presence of4mT MF, Q235showed the same corrosion evolution as in the control, but the amplitude of EN current was much bigger, suggesting serious corrosion. The extension of local corrosion became more and more serious with the development of SRB biofilm. Different from the diamagnetism304SS, the paramagnetism Q235can be easily magnetized, the magnetized carbon steel enhanced the intensity of the magnetic filed. The enhanced MF accelerated the corrosion of Q235.3) Effect of MF on Q235with imposed stress:In the sterile culture medium, the corrosion of Q235underwent three stages:general corrosion in the biofilm lag phase; metastable corrosion in the biofilm log phase and the corrosion cracking in the bioflim decline phase. In the SRB solution, the corrosion cracking happened in the biofilm log phase, which indicated that SRB promoted the corrosion cracking of Q235. In the presence of4mT MF, the corrosion cracking happened at the biofilm lag phase, and passivation took place during the biofilm log phase, however, corrosion cracking appered agiain at the biofilm decline phase. The fracutre mode of Q235belongs to brittle fracture. Different from the discontinuos cracking, the continuous cracking happened in the presence of150mT MF. This could be related the energy supply by MF. In conclusion, he synergism between MF and SRB greatly accelerated and worsened the corrosion of Q235. |
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