Page 294 - Corrosion Engineering Principles and Practice

268 C h a p t e r 8 C o r r o s i o n b y W a t e r 269

Winch system

Electronic
control box

Droud
Water flow
Hydrophone
Large diameter pipe

FIGURE 8.4 Schematic description of the Water Research Center’s large-
diameter pipe leak detection system [7].
Acoustic leak detection methods such as illustrated in Fig. 8.4 may
find already broken or damaged pipes [7]. However, corrosion
monitoring possibly may identify areas where corrosion activity on
pipes is likely while the remote field effect can inspect pipes to find
damage before they fail. A complete diagnostic program is likely to
use all these inspection methods.

8.3 Types of Water
Water is commonly described either in terms of its nature, usage, or
origin. The implications in these descriptions range from being highly
specific to so general as to be non-definitive. A more practical description
consists in classifying waters according to composition, for example,
fresh containing less than 1000 ppm chlorides, brackish having 1000 to
25,000 ppm chlorides, seawater having between 2.5 and 3.5 percent
sodium chloride, and brines with still higher chloride concentrations [8].
The corrosive nature of waters varies considerably depending
largely on their composition and on the alloy exposed to the aqueous
environment. Also very important in many cases is the biological
activity of myriad aquatic organisms, whose metabolic products are
directly or indirectly corrosive to many metals.

8.3.1 Natural Waters
Natural waters have large seasonal variations in physical, chemical,
and biological characteristics. Oxygen, nutrients, pH, and other
factors important for fouling and corrosion vary on a more or less
predictable schedule during what is known as the “turnover.” Any