Environmental Engineering Reference
In-Depth Information
Figure 3.61
Tubercules formed due to microbial activities in carbon steel pipe.
during rainy seasons. Thus, sulfur-oxidizing bacteria and sulfate-reducing bacte-
ria may grow in cycles causing continuous damage to the underground structures.
3.10.2 Macrofouling
Macrobiological organisms, such as shells, mollusks, barnacles, etc., cause both
fouling and corrosion of metallic structures, vessels, and pipelines exposed to
seawater as well as freshwater. Fouling is often more important than the attendant
corrosion. These organisms remain attached to the metal surface, and their accu-
mulation at the bottom of a ship's hull increases the drag and power requirement.
In heat exchangers, such accumulations may clog the pipeline and impair fluid
flow as well as heat transfer. Stagnant and low rate of fluid flow are conducive
to biofouling.
Biofouling contributes to corrosion in several ways. The underlying metal
remains sheltered from dissolved oxygen, and a crevice condition is created. The
metabolic byproducts of these organisms are often acidic and hence corrosive.
Moreover, the anaerobic conditions prevailing underneath the macroorganisms
can favor the growth of anaerobic bacteria which, in turn, accelerate corrosion
of the metal.
3.10.3 Remedial Measures
For Microbiological Corrosion
1.
Aeration and chlorination
. It is important to identify the type of bacteria
involved in corrosion through culturing. Aeration of water in a closed or
recirculating system reduces the activity of anaerobic bacteria. Chlorination
and treatment with biocides help control populations of some bacteria,
