Page 277 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

WATERWAYS AND PORTS 255

4.12.1 Pipe Failures
Low-pressure gas distribution pipeline failures result in leaks rather than catastrophic
ruptures. The main concern is that a leak goes undetected and the gas collects in a
confined space, eventually igniting and causing an explosion.

4.12.2 Plastic Pipe
It is sometimes suggested that plastic pipe is safer than steel pipe because of corrosion
of steel pipe. The aging or degradation of plastics may play an important role in
plastic pipe failures. The degradation processes that lead to plastic pipe failures in
operation are not well documented. The vulnerability of older plastic gas distribu-
tion pipe to brittle-like cracking has brought to light that plastic pipe is susceptible
to certain aging and degradation processes. The brittle-like cracking in plastic pipe
relates to a part-through crack initiation in the pipe wall followed by stable crack
growth at stress levels much lower than yield stress, resulting in a very tight slit-like
opening and gas leak. Although significant cracking may occur at points of stress
concentration and near improperly designed or installed fittings, small brittle-like
cracks may be difficult to detect until a significant amount of gas leaks out of the
pipe and potentially migrates into enclosed spaces such as a basement. Premature
brittle-like cracking requires relatively high localized stress intensification that may
result from geometric discontinuities, excessive bending, improper fitting assemblies,
and/or dents and gouges. The older polyethylene piping manufactured from the 1960s
through the early 1980s may fail at lower stresses and after less time than was origi-
nally projected.

4.13 WATERWAYS AND PORTS

The United States has more than 7750 commercial water terminals, 192 commer-
cially active lock sites with 238 chambers, and 40,000 km of inland, intracoastal, and
coastal waterways and canals; 41 states, 16 state capitals, and all states east of the
Mississippi River are served by commercially navigable waterways. Public and pri-
vate works associated with waterways and ports have corrosion-related problems in
both freshwater and seawater environments.
The reinforced concrete structures exposed to marine environment suffer prema-
ture corrosion-induced deterioration by chloride ions in seawater. Corrosion is typ-
ically found in piers and docks, bulkheads and retaining walls, mooring structures,
and navigation aids.
The marine environment can have varying effects on different materials depend-
ing on the specific zones of exposure. Atmosphere, splash, tide, immersion, and
subsoil have very different characteristics and therefore have different influences on
corrosion.
Atmospherically exposed submerged zones typically experience the greatest
corrosion. These zones are found on piers and docks (ladders, railings, cranes, and