Page 196 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

174 CORROSION CAUSES

more than 120 million low-carbon steel roof bolts are used per year and are a major
area of concern with regard to corrosion because a failure of the roof bolt is hazardous
and could result in the loss of lives (25). In sulfide mines, roof bolts have been reported
to fail within 1 year because of sulfide SCC.
Corrosion within pump and piping systems is another critical issue in the mining
and mineral processing industries. The most common form of corrosion is uniform
corrosion; however, pitting, crevice corrosion, intergranular corrosion dealloying,
galvanic corrosion, and cavitation are each possible depending on the processing
environment. Erosion–corrosion in ore grinding mills is another critical issue.
Particulates are often carried in a corrosive medium through pipes, tanks, and pumps.
The presence of these particulates erodes and removes the protective film of the
metal and exposes the reactive alloy to high-flow velocity, thus accelerating the
corrosion.
According to the Connoisseur Corporation Pty. Ltd. (29), the effects of corrosion in
electrical and electronic systems in modern mines are often overlooked; however, the
harsh environment of the mining industry often causes failure of electrical equipment
after a short period of time.
Pyrite and other sulfide minerals on exposure to oxygen and water are oxidized to
produce ferrous ions and sulfuric acid. The ferrous ions further react to form hydrated
iron oxide and hydrogen ions. The hydrogen ions lower the pH of water, making
it deleterious to aquatic life and corrosive to surrounding structures. The acid mine
drainage can cause corrosion problems in structures such as pipes, well screens, dams,
bridges, water intakes, and pumps. A survey made in 1993 by the US Forest Service
estimated that 8050–16,100 km (5000–10,000 miles) of domestic streams and rivers
are impacted by acid mine drainage (30).
In comparison, in 1995, the Pennsylvania Department of Environmental
Protection reported that 3902 km (2425 miles) of stream in Pennsylvania did not
meet EPA-mandated in-stream water quality standards because of mineral extraction
(31). This significant amount affected streams in Pennsylvania, compared with
the nationally estimated amount, can be explained by the fact that this state has a
relatively large portion of the US coal industry.

3.24 PETROLEUM REFINING

The petroleum refining industry is undergoing intense scrutiny in the United
States of America from regulatory agencies and environmental groups. The total
cost of corrosion control in refineries is estimated at $3.692 billion. The costs
associated with corrosion control in refineries include both processing and water
handling.
Corrosion-related issues regarding processing are handling organic acids [also
referred to as naphthenic acid corrosion (NAC)] and sulfur species at high tempera-
tures as well as water containing corrosives such as H S, CO , chlorides, and high
2 2
levels of dissolved solids.