Page 195 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

CORROSION IN THE MINING INDUSTRY 173

mine atmospheres and waters are unique and vary widely from one mine to another;
therefore, each mine experiences relatively different corrosion-related problems.
Aerobic and anaerobic microorganisms present in mine water also contribute to
the extremely corrosive environments (25). Aerobic species produce sulfuric acid,
making the environment very acidic. Aerobic microorganisms reduce sulfate and sul-
fides by using available hydrogen and producing hydrogen sulfide.
Although corrosion exists in the mining industry, the industry does not consider it
to be a serious issue. Engineers from several mining companies who were interviewed
could not provide any information on instances where corrosion problems were a
critical issue. Past experiences and equipment suppliers provide the process engineers
with enough information to keep the mining industry processing its metallic minerals,
industrial minerals, and coal.
While mining engineers are not involved in serious corrosion issues, literature
on the subject lists several areas of major concern because of personnel safety and
continuation production. The areas of major concern are the following:
1. Wire rope
2. Roof bolts
3. Pump and piping systems
4. Mining electronics
5. Acid mine drainage.

3.23.1 Wire Rope

Wire ropes are used extensively in the mining industry to help hoist equipment. Mine
workers also depend on this rope for their safety. Wire rope undergoes both corro-
sion and abrasion, which will degrade the mechanical properties of the wire and thus
reduce its load-bearing capability and cause it to fail.
A statistical study of mine-hoist wire ropes showed that 66% of the ropes exhibited
greatest loss in strength in the portion of the rope in contact with the shaft environment
during its service life (26). The Mine Safety and Health Administration (MSHA) of
the US Department of Labor requires that wire ropes in service be visually examined
for structural damage, corrosion, and improper lubrication or dressing (27). MSHA
also requires performance of careful nondestructive testing (NDT) every 6 months
and cites one instance where a contractor reported that four ropes were in acceptable
condition for use in an elevator shaft. However, less than 6 weeks later, one of the
four 12.7 mm (0.5 in.) diameter ropes broke and another was severely corroded with
several broken wires (28).
Wire ropes within the mining industry are routinely replaced every 18–36 months
depending on environmental conditions and use over time. The wire ropes are made of
carbon steel; however, because of their susceptibility to corrosion and wear, stainless
steel and synthetic fiber ropes are becoming more widely used instead of carbon steel
ropes (25).
In the mining industry, roof bolts provide support in underground mines by tying
the lower layer to a stronger layer located above the main roof. In the United States,