Page 266 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

244 CORROSION CONTROL AND PREVENTION

$3.79 billion to replace structurally deficient bridges over 10 years; $2.93–1.07 billion
for maintenance and cost of capital for concrete bridge decks and $2.93–1.07 billion
for maintenance and cost of capital for concrete substructures and superstructures;
$0.5 billion for maintenance painting cost for steel bridge. The average annual cost
of corrosion of bridges amounts to $8.29 billion.
The cost of corrosion can be greater in the case of historically significant bridges
and bridges that are critical to traffic flows. In addition, problems in posttensioned
bridges or cable and suspension bridges can be very costly to repair. Although the
direct costs presented are estimated costs based on broad assumptions, the calculated
cost represents the relative cost of corrosion for the highway bridge industry sector.
Life-cycle analysis estimates indirect costs such as traffic delays and lost productivity
at ten times the direct cost of corrosion.

4.10 MITIGATING CORROSION OF REINFORCING STEEL IN
UNDERWATER TUNNELS (36)

Corrosion of the outermost rebar may be mitigated by installing CP; however, a con-
ventional CP system with anodes installed on the concrete surfaces likely will not
be effective because of a dry environment at the anode-concrete interface that does
not facilitate current flow caused by electrochemical osmosis. Because the interior of
the tunnel is not exposed to rain or splashing sea water, the moisture available would
come from the air. Water from inside the concrete would not reach the surface anodes
because the surface cracks were sealed.
To address this type of corrosion mitigation problem, a specialized CP system was
developed that can minimize the drying effect at the anode/concrete interface without
direct water exposure. By creating a low-resistance anode interface using a semicon-
ductive layer the effect of electrochemical osmosis at the anode/concrete interface
can be minimized, so that the CP system is not dependent on water or moisture from
the outside environment and can also operate at low voltage. In addition, the semicon-
ductive layer would minimize acid generation if the anode comes into direct contact
with saltwater present because of new water leakages.

4.11 CORROSION OF UNDERGROUND GAS AND LIQUID
TRANSMISSION PIPELINES

Corrosion of the pipe wall can occur either internally or externally. Internal corrosion
occurs when corrosive liquids or condensates are transported through the pipelines.
Depending on the nature of the corrosive liquid and the transport velocity, different
forms of corrosion may occur, including uniform corrosion, pitting/crevice corrosion,
and erosion–corrosion.
There are several different modes of external corrosion identified in buried
pipelines. The primary mode of corrosion is a macrocell form of localized corrosion
because of the heterogeneous nature of soils, local damage of the external coatings