Stainless steel in coastal seawater: sunlight counteracts biologically enhanced cathodic kinetics

The influence of sunlight of varying intensity on the performance of UNS S30400 stainless steel (SS) was explored under conditions of natural biofilm development in coastal seawater. In a series of tests performed outdoors under an opaque roof, a range of shades were fashioned to impart varied amoun...

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Published inBiofouling (Chur, Switzerland) Vol. 30; no. 8; pp. 929 - 939
Main Authors Eashwar, M., Lakshman Kumar, A., Sreedhar, G., Kennedy, J., Suresh Bapu, R.H.
Format Journal Article
LanguageEnglish
Published England Taylor & Francis 14.09.2014
Subjects
Bacterial Physiological Phenomena
biofilm
Biofilms - growth & development
cathodic kinetics
Corrosion
Darkness
Electrodes
India
Kinetics
manganese
Manganese - metabolism
seawater
Seawater - chemistry
stainless steel
Stainless Steel - radiation effects
Sunlight
India
cathodic kinetics
sunlight
seawater
stainless steel
manganese
biofilm
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Summary:The influence of sunlight of varying intensity on the performance of UNS S30400 stainless steel (SS) was explored under conditions of natural biofilm development in coastal seawater. In a series of tests performed outdoors under an opaque roof, a range of shades were fashioned to impart varied amounts of diurnal light. These were an ambient level where the underwater illumination was ~ 5% of full sunlight, two intermediate ranges of lighting with ~ 2.5% and ~ 1% of the daylight, and a condition of full darkness. In comparison with the dark, increments of sunlight rendered the SS progressively less aggressive as cathodes in galvanic couples with UNS C70600 alloy. Likewise, welded SS with pre-initiated localized corrosion sites exhibited substantially lower rates of propagation with light. Thus, biofilms and sunlight affected cathodic kinetics in opposite ways. Surface analytical tests showed that the accumulation of manganese (Mn) within the biofilms was small relative to reports from waters of lower salinity. These results not only reveal that extremely low amounts of sunlight are adequate to offset the microbial effect, but also highlight the lack of convincing evidence for Mn cycling as a potent mechanism for enhanced cathodic kinetics in full-strength seawater.
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ISSN:0892-7014
1029-2454
DOI:10.1080/08927014.2014.952632