Page 458 - Corrosion Engineering Principles and Practice

424 C h a p t e r 1 0 C o r r o s i o n i n S o i l s a n d M i c r o b i o l o g i c a l l y I n f l u e n c e d C o r r o s i o n 425

FIGURE 10.12 Oil recovery microbial test lines to evaluate biocide programs.
(Courtesy of Kingston Technical Software)

The assumption is generally made that a system showing extensive
fouling is prone to MIC. Systems with extensive fouling are operating
inefficiently and may in any case warrant remedial action.

Electrochemical Methods An electrochemical method for on-line
monitoring of biofilm activity has been developed for continuous
monitoring of biofilm formation without the need for excessive
involvement of plant personnel [Figure 10.13(a) and 10.13(b)]. The
series of stainless steel or titanium disks in the monitoring device are
exposed to the plant environment with only one set of disks being
polarized relative to the other sets for a short period of time each
day. The electrodes are typically connected through a shunt the
remainder of the time. Biofilm activity, which is also an electrochemical
process, is monitored by tracking changes in the applied current
when the external potential is on and the generated current when the
potential is off [12].
The onset of biofilm formation on the probe is indicated when
either of these independent indicators deviates from the baseline
level (Fig. 10.14). Such a departure would then trigger the alarm
located in a control box (Fig. 10.15). The level of biofilm activity is
also measured by the amount of variations from the baseline assuming
that the applied and generated currents from a well-controlled system
produce typically a flat line devoid of any significant deviations.
Another experimental approach to detect MIC with an
electrochemical signals is based on the use of small silver sulfide and
silver chloride electrodes capable of detecting sulfides or chlorides
by changes in the potential between the Ag/AgCl or Ag/Ag S
2