Detection of Microbial sulfate-reduction associated with buried stainless steel coupons Page: 4 of 12
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The NBS experimental design for the buried coupon study included several different
treatments for each metal type. Treatments were designed to sensitize or otherwise
compromise some coupons to simulate the results of container fabrication and/or to accelerate
the effects of long-term burial. Four coupons representing 3 stainless steel (SS) types were
selected for the present microbiology study. This group consisted of untreated coupons of
types 301, 304 and 316 SS and one of type 316 sensitized. Sensitization consisted of heating
to 12000 F for 2 hours, followed by cooling in ambient air, de-scaling in sodium hydroxide, and
passivating in concentrated nitric acid to establish a thin surface oxidation layer'.
At inception of the study in 1970, the burial site near Wildwood, NJ was described as
coastal dune environment with strong marine influence. At the time coupons were recovered
in 2004, the site was a densely vegetated back-dune environment sheltered from direct ocean
exposure. Mean annual rainfall was 104 cm, and temperature ranged between -1 and 270 C.
The predominant vegetation now consists of woody shrubs that present a nearly complete 3 m
over-story. A moderate under-story of mixed vegetation is also present. The soil is a light
Collection and Handling of Coupons
The 20 x 30 cm coupons were buried 76 cm deep in parallel rows of 20 coupons 30 cm
apart. Coupons for microbiological study were given special care during handling to prevent
contamination. Surgical gloves were worn during the last stages of uncovering, removal and
packaging. Coupons were immediately placed in sterile plastic bags, double wrapped in heavy
gage polyethylene bags, placed in a 40 C cooler, and immediately shipped to INL. On arrival
at the laboratory coupons were placed in storage at 40 C in an oxygen free nitrogen
atmosphere. Experiments were initiated within 10 days of arrival.
Silver Foil Method
Ten cm squares (100 cm2) of silver foil used for imaging were prepared for sulfide
capture by cleaning with successive washes of ethanol, acetone and hexane, and their
surfaces were sensitized for reactivity to sulfide by treatment with concentrated nitric acid then
rinsed repeatedly with filter-sterilized de-ionized water.
Four coupons that showed visible signs of beginning corrosion were selected for
imaging. These coupons were stainless steel types 301, 304, 316, and 316 sensitized. Ten
cm square areas of interest on coupons were cleaned with a soft bristle % inch diameter
camel's hair brush(2) and blown with dry filtered nitrogen gas to remove loose soil particles.
These areas were then coated with a solution containing Na35SO4 and 1 mM sodium lactate
solution sufficient to wet the area of interest without run-off. Final sulfate concentration on the
coupon was 0.05 mM with a net 35S activity at the start of the experiment of 2 pCi per foil.
Sensitized silver foils backed by foam blocks cut to match were placed on the coupons and
(2) Fisher Scientific model 03-661
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Delwiche, Mark E.; Flitton, M. Kay Adler & Olson, Alicia. Detection of Microbial sulfate-reduction associated with buried stainless steel coupons, article, March 1, 2007; [Idaho Falls, Idaho]. (digital.library.unt.edu/ark:/67531/metadc888535/m1/4/: accessed September 25, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.