Microbiologically Induced Corrosion And Its Control In Cooling Water System

Microorganisms can grow and multiply rapidly in cooling water systems due to its enclosed structures, favorable temperatures and nutritional environments. This may readily cause serious problems like pitting corrosion, low heat transfer efficiency or pipe blockage. Sulfate reducing bacteria (SRB) is one of the main microorganisms in microbiologically induced corrosions (MIC). Stainless steel has been applied for cooling systems in recent years, which can suffer sever MIC in the presence of SRB. In this paper, electrochemical measurements and surface analysis techniques were used to investigate corrosion characteristics of 316L stainless steel (SS) in simulated cooling water with SRB. The primary results are as follows:1. The corrosive effect of SRB for stainless steel in simulated cooling water was investigated. EIS results showed that resistance values of SS electrodes increased with the increase of immersion time in sterile media, while decreased in non-sterile media. Polarization curves results revealed that passive current densities of SS in non-sterile media increased with the immersion time. After 8 days of immersion, passive current density was one order of magnitude higher than that in sterile media, which suggested that SRB had a strong erosive effect on SS.2. Corrosion of SS in both non-sterile and S2--containing sterile media were analyzed and compared. It showed that SS had less resistance values and greater passive current densities in non-sterile cooling water compared with that in S2--containing sterile media. SEM/EDS results indicated that an uneven distributing biofilm formed on the SS surface after immersion in non-sterile media. It appeared pittings on the metal surface after removing of biofilm. This suggested that SS corrosion by SRB were also related to the formation of biofilm.3. The inhibition behaviors of glutaric dialdehyde, polyhexamethylene guanidine (PHMG) and electromagnetic techniques for SRB corrosion were studied, respectively. Results indicated that the use of three methods increased the resistances and decreased the passive current desities of SS electrode with the increase of glutaric dialdehyde and PHMG concentrations and the time of electromagnetic treating, showing good inhibitive effects.4. Theoretical calculations of adhesive works between biofilm and SS further revealed the inhibition mechanism of three methods. The adhesive works grew form 20.73 mJ·m^-2 for the first day to 30.93 mJ·m^-2 for the 12th day of immersion in non-sterile media. After SS attached with biofims immersed by glutaric dialdehyde, adhesive works incresed with agent concentrations. When treated by PHMG and electromagnetic process, adhesive works decreased gradually, and reached the minimum 9.97 mJ·m^-2 at 50 mg/L PHMG and 1.58 mJ·m^-2 at 60 min for treating time, respectively. SEM/EDS results indicated that biofilm on the SS surface reduced obviously after using PHMG and electromagnetic process, while remained an amount biofilm after dealing with glutaric dialdehyde.