Environmental Engineering Reference
In-Depth Information
though they are not effective in all cases. Also, the bacteriocides fail to reach
the areas underneath deposits where the bacteria thrive.
2.
Coatings
. Coating the buried structure with tar, enamel, plastic, or the like
is often an effective means to preclude the bacteria from the metal surface.
3.
Cathodic protection
. Cathodic protection in combination with coatings can
be used to prevent or arrest microbiological corrosion.
4.
Maintenance
. During storage or after hydrotesting, water should not be al-
lowed to stand for a long period. Complete drainage and drying up are advo-
cated. Inhibitors may be used in stagnating water and cutting-oil fluids. Peri-
odic cleaning of pipelines is also essential.
5.
Substitute materials
. In worst affected soils, steel pipes may be replaced by
asbestos or plastic pipes to avoid microbiological corrosion.
For Macrobiofouling
1.
Paints
. The application of antifouling paints is probably the most effective
and most widely used means to prevent biofouling in sea water. Ships and
piers are coated with specially formulated paints containing compounds toxic
to the organisms. Copper compounds are often used, as the released copper
ions poison the growth of barnacles and other marine organisms.
2.
Cleaning
. Periodic mechanical cleaning of surfaces of structures and inside
of pipelines help reduce the growth of bioorganisms and the creation of crev-
ice sites.
3.
Use of biocides
. In closed systems, fouling can be mitigated by chlorination
and periodic injection of suitable biocides, including copper compounds.
3.10.4 Practical Examples
Figure 3.16 illustrates a crevice corrosion attack on stainless steel in seawater as
a result of barnacle attachment. Microbiological corrosion has been reported [8]
to be encountered in stainless steel tanks, pipelines, and flanged joints, particu-
larly in welded areas after hydrotesting with natural river or well waters in chemi-
cal processing industries as well as in nuclear power generation. Copper-nickel,
brass, and aluminum-bronze pipes and tubes are also affected. Sulfate-reducing
bacteria have been observed to cause damage to buried steel pipelines, particu-
larly in oil fields. It has been reported [55] that a well water caused failure of 2-
in. -diameter galvanized water pipe within 2 years by the action of sulfate-reduc-
ing bacteria, whereas municipal water employing similar wells, but chlorinated
beforehand, was much less corrosive.
REFERENCES
1.
V. J. Colangelo and F. A. Heiser,
Analysis of Metallurgical Failures
, John Wiley
and Sons, New York, p. 182, 1974.
