Definition:
Piles are structures used to
transfer loads from superstructure to the sub surface strata. When the
subsurface stratum is water based or if we deal with a hydraulic structure, the
piles are to be driven into water and under water strata. Piles used in
underwater structures are often subjected to corrosion.
There is no absolute
way to eliminate all corrosion; but corrosion protection measures are employed
to control the effect of corrosion. Corrosion protection can be in different
ways according to the environment and other factors. Forms of corrosion
protection include the use of inhibitors, surface treatments, coatings and
sealants, cathodic protection and anodic protection. The control measures
explained in this are Protective coatings, cathodic treatment and application
of Fibre Re-inforced Polymer (FRP) Composites.
Corrosion Mechanism Of
Steel In Sea Water:
On
steel piling in seawater, the more chemically active surface areas (anodes)
are metallically coupled through the piling itself to the less chemically
active surface areas (cathodes) resulting in a flow of electricity and
corrosion of the anodic areas. General surface roughening occurs when these
local anodic and cathodic areas continually shift about randomly during the
corrosion process. Sometimes these active local areas do not shift position
end, therefore, the metal suffers localized attack and pitting occurs. In
general, the depth of pitting is related to the ratio of the anodic sites to
the area of cathodic site in contact with the electrolyte (seawater). The
smaller the anode area relative to the cathode area, the deeper the pitting.
Corrosion Management:
Before deciding on the
methods for control of corrosion to be applied, conceptual and feasibility
studies have been carried out. Typically, corrosion management can be divided
into three major phases.
Phase 1 of the program
is the programmatic assessment of the project. This phase is the planning stage
for a corrosion management program to take place. It initiates the
program to be implemented on structures that are found to be under the threat
of corrosion. For the planning stage, three main requirements are sought,
namely the strategy, budget and schedule needed to overcome the problem raised
from corrosion of reinforcement. This is seen as an important part for an
effective management program as feasibility studies are normally conducted to
determine the serviceability of the structure after treatment.
Phase 2 of the program
involves physical assessment and actual remediation. Inspections for severity
of corrosion are conducted in this phase to determine what strategy or methods
are most suitable to be applied. Development of corrosion control strategy
would present more option to the management program. Remedial work would be
carried out once the proper strategy has been recognized.
Phase
3 of the program mainly deals with future monitoring of the repaired structure.
Currently and historically, most of the corrosion control programs are driven
by response to incident or urgent need, rather than systematically identifying
and managing the existing resources. This can be overcome by implementing
internal or external monitoring system using current technology practiced in
oil and gas industries.
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