control of corrosion on underwater piles
TRANSCRIPT
CONTROL OF CORROSION ON UNDERWATER PILES
Submitted to: Submitted by:
Dr . J.K. Sharma Poonam Shekhawat
Asso. Professor (09/264)
Department of Civil Engineering
University College of Engineering
Rajasthan Technical University, Kota
INTRODUCTION Corrosion is the destruction of metals and alloys by the
chemical reaction with the environment or it may be regarded as the reverse process of extraction of metals from ore.
Generally many traditional metal parts are used with lighter polymeric components but these are impervious to electrochemical corrosion so even with the proper selection of base metals, there is no absolute way to eleminate corrosion.
Forms of corrosion protection include the use of inhibitors, surface treatments, coatings and sealants, cathodic protection and anodic protection.
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 flow of electricity and corrosion of anodic areas.
Generally corrosion occures when local anodic and cathodic areas continually shift about randomly but sometimes they do not shift position end, therefore the metal suffers localized attack and pitting occurs.
In general smaller the anode area relative to the cathode area, the deeper the pitting
CORROSION CAUSED BY THE DIFFERENCE OF THE DISSOLVED OXYGEN (DO) CONCENTRATION
ZONES OF CORROSION OF STEEL PILES
ZONES
SPLASH
ZONE
ATMOSPHERIC
ZONE
SUBMERGE
DZONE
TIDAL
ZONE
Depending upon time of wetness, temperature, pollutants etc. Atmospheric corrosion is responsible for a large fraction of the total corrosion in the world.
CORROSION RATE(without protection)
< 0.1 mm/year
ZONES
SPLASH
ZONE
ATMOSPHERI
CZONE
SUBMERGED
ZONE
TIDAL
ZONE
The splash/spray zone can be characterized by as an aerated sea water environmentWhere exposed material are almost continually wet and biofouling do not attach.
CORROSION RATE(without protection)
0.3 mm/year
ZONES
SPLASH
ZONE
ATMOSPHERI
CZONE
SUBMERGED
ZONE
TIDALZONE
The tidal zone is an environment where metals are alternately submerged in seawater and exposed to the splash zone as the tide fluctuates.
CORROSION RATE(without protection)
0.1-0.3 mm/year
ZONES
SPLASH
ZONE
ATMOSPHERI
CZONE
SUBMERGED
ZONE
TIDALZONE
The submerged/shallow ocean environment zone usually characterized by well aerated water combined with marine biofouling organism of both the plant and animal variety.
CORROSION RATE(without protection)
0.1-0.2 mm/year
CORROSION MANAGEMENT Phase 1 of the
program is the programmatic assessment or planning stage of the project.
For the planning stage,three main requirements sought, budget and schedule needed to overcome the problem raised from corrosion of reinforcement.
PHASE 1
PHASE 2
PHASE 3
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.
PHASE 1
PHASE 2
PHASE 3
Phase 3 of the program mainly deals with future monitoring of the repaired structure.
Systematically identifying and managing the existing resources can be done by implementing internal or external monitoring system using current technology.
PHASE 1
PHASE 2
PHASE 3
CORROSION PROTECTION METHODS
PROTECTIVECOATING
CATHODICPROTECTIO
N
ANODE DELIVERY SYSTEM
Application of FRP
composites
PROTECTIVE COATINGS
1. •Inorganic Zinc Sillicates Primers
2. •High Build Epoxy Coatings
3. •Aliphatic Polyurethane Topcoats
4. •Zinc Rich Epoxy Primers
5. •Non-Skid Deck Coatings
CATHODIC PROTECTION Cathodic protection is an electrochemical
process which halts the corrosion of metals in a particular environment by superimposing an electrochemical cell more powerful than the corrosion cell.
Sacrifical Anodes are fitted or bonded to the metal to be protected.
The implementation is simple, all you need is an anode, a power supply and engineering talent.
ANODE DELIVERY SYSTEM Pile Mounted Anode Retractable Anode
Sled Anode Suspension Anode
APPLICATION OF FRP COMPOSITES
The poor durability of conventional corrosion repairs has led to increased interest for its replacement by fiber reinforced polymers.
Although dry conditions are favorable but availability of resins that can cure in water has made it possible.
Saturating FRP with resin and installing is complex but benificial in costly repairs and rapid deterioration.
Fibre reinforced polymers have long been used for the repair and retrofit of concrete structural elements.
Lightweight, high strength and resistance to chemicals.
Unparallel flexibility, multi-directional.
Twofold role: first to restore lost flexural capacity and second to provide resistance to withstand expansive forces.
Figure shows impact damage that led to both cross-section and breakage of the spiral ties.
Using FRP there is only need to re-form the cross-section and apply bi-directional layers to restore lost tensile capacity.
Bonding agents may be required to assure capillary suction of the epoxy and to ensure good bond.
CONCLUSION
Though there is no absolute way to eliminate all corrosion on underwater piles, there are some effective measures to control them.
Cathodic protection is quit simple and protective coatings are used in vast and expensive structures.
The FRP composites have many advantages viz. lightweight, posses high strength and chemical resistance and moreover have incomparable flexibility.
Of the various ways of wrapping of FRP composites , transverse wrapping is found to be the easiest.
