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state as the main parameter mea- sured by the authors) become active we will need anaerobic (oxygen- free) environments, this makes it hard to believe that SRB were the main and only cause of producing excess H2
S gas.
2) Under absence or deficiency of oxygen, the redox potential (Eh
for reducing ferric to ferrous ions is <300 mV whereas the one for reducing sulfate into H2
mV.5 Therefore, even if oxygen is
being depleted slowly in the pipe envQZWVUMV\ Q\ Q[ M`XMK\ML \W ÅZ[\ get iron oxides and then H2
S. This
is indeed what has been observed and reported by the authors too. Therefore, it may be concluded that the potentials have not yet entered into the range necessary for sulfate reduction. Magnetite is a good sign to show that there has been an excess of oxygen. I was personally involved in a case relatively similar to this case last year where while the existence of some bacteria in the system had been reported, our ÅVIT KWVKT][QWV _as that the corro- sion was due to an excess of oxygen and was not microbiologically in- Æ]MVKML KWZZW[QWV 51+ ZMTI\ML
3) Even if we accept that SRB were the main cause of excess H2
S gas
production, the particular condi- tions of the pipe would more or less resemble that of a closed sys- tem. Under these circumstances, the poisonous gas will also kill the bacteria unless the gas is consumed or ventilated out. The limitation of the microorganisms in the seawater to SRB (which in essence is unre- alistic) by the authors removes the possibility of consumption of the gas by other microorganisms such as sulfur oxidizing bacteria (SOB).
4) However, seawater is a biochemical "soup" in which several types of mi- croorganisms could exist, including but not limited to SOB. As we have shown,4
together to produce H2 10 MATERIALS PERFORMANCE November 2012 ) S is <100
5) The authors rely on the excess of H2
S as well as the absence-presence
tests and enumeration tests to sug- gest the existence of SRB and their serious involvement as the main factors in enhancing the produc- tion of H2
S. However, they have
not addressed in any of their three papers any indication for consider- QVO \PM XW[[QJQTQ\a WN QLMV\QÅKI\QWV WN W\PMZ \aXM[ WN 51+ ZMTI\ML JIK\MZQI or even non-microbial sources of H2
S production (such as decay of
the marine organisms and animals within the pipe as a result of the disturbed seawater that has entered into the pipe segment as a result of the hurricane).
As a result, I think it will be wrong
to assume that SRB was the only culprit in producing too much H2
S and other
possibilities in addition to SRB need to be investigated and reported.
References
1 D. Powell, D. Fincher, R. Gonzales, B. Melancon, R.H. Winters, B. Rodrigue, - *ZW_V ¹1VQ\QIT +WZZW[QWV 8ZWL]K\[ Protect a Pipeline from Microbiologi- cally Generated H2
S," MP 51, 8 (2012).
, 8W_MTT : -QVMZ 2 +PMMS D. Fincher, R. Gonzales, R.H. Winters, * :WLZQO]M * 5MIV[ +7::7;176 2010 paper no. 10064 (Houston, TX: 6)+- 1V\MZVI\QWVIT
, 8W_MTT : -QVMZ 2 +PMMS D. Fincher, R. Gonzales, R.H. Winters, B. Rodrigue, B. Means, Oil and Gas J. 108, 16 (May 3, 2010).
4 R. Javaherdashti, 5QKZWJQWTWOQKITTa 1VÆ]- enced Corrosion—An Engineering Insight 6M_ AWZS 6A" ;XZQVOMZ
5 "Microbiological Degradation of Materi- IT[ IVL 5M\PWL[ WN 8ZW\MK\QWV º -.+ 6W !