CONTROL 0F CORROSION ON UNDERWATER PILES PRESENTED BY:Lakshay saxena1302900059
Content INTRODUCTIONCORROSION PROTECTION METHODSSTANDARDS AND CODESCONCLUSION REFERENCES
Corrosion is the destruction of metals and alloys by the chemical reaction with the environment. During corrosion the metals are converted to metallic compounds at the surface and these compounds wears away as corrosion product.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.
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.
Sometimes these active local areas 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, Pitting is deeper.
ZONES OF CORROSION OF STEEL PILES
Corrosion Caused By The Difference Of The Dissolved Oxygen Concentration
Depending upon time of wetness, temperature, pollutants, Atmospheric Corrosion is responsible for a large fraction of the total corrosion.
Corrosion rate is least in this zone(without protection) < 0.1 mm/year.
Paints and Coatings are used in protecting this section.
The Splash zone can be characterized by as an aerated sea water environment where exposed material are almost continually wet.
Corrosion rate (without protection) 0.3 mm/year.
This zone is alternately submerged in seawater and exposed to Splash zone as the tide fluctuates.
Corrosion rate (without protection) 0.1-0.3 mm/year.
The submerged environment zone usually characterized by well aerated water combined with marine bio fouling organism of both the plant and animal variety.
Corrosion rate (without protection) 0.1-0.2 mm/year.
CORROSION MANAGEMENTIt is divided into three major phases:
Phase 1 of the program is planning stage of project.For the planning stage ,three main requirements strategy, budget and schedule needed to overcome the problem raised from corrosion of reinforcement
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 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.
CORROSION PROTECTION METHODS
Protective CoatingIn order to protect metals from corrosion, the contact between the metal and the corrosive environment is to be cut off. This is done by coating the surface of metals with a continuous non-porous material inert to the corrosive atmosphere.
Surface coatings are broadly classified into threeMetallic coatingsInorganic CoatingsOrganic Coatings
Protective Coatings Inorganic Zinc Sillicates PrimersAliphatic Polyurethane TopcoatsHigh Build Epoxy CoatingsZinc Rich Epoxy PrimersNon-Skid Deck Coatings
Epoxies are generally more abrasion and chemical resistant than primersThese are poor resistance of ultra violet from sunlight and most will chalk and fade rapidly.High Build Epoxy Coatings
optimum resistance to UV and high degrees of flexibility and chemical resistance.maintain a very high level of cosmetic gloss and color retention and can be cleaned very easily with low pH detergents and fresh water pressure washing.Aliphatic Polyurethane Topcoats
normally incorporate very course aggregates for an exaggerated profile. They are applied in very high film builds and normally without a zinc rich primer. Non-Skid Deck Coatings
CATHODIC PROTECTIONCathodic 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.
These are similar to the cathodic protection method in philosophy.These are designed on the design basis of maximum current distribution for the lowest possible cost, with the most long-term reliability.
Anode delivery systemPile Mounted AnodeRetractable Anode
Sled AnodeSuspension Anode
Application of FRP compositesThe 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.
Pile surfaces were covered with marine growth that had to be scraped off. Additionally, two of the four corners that were not rounded but chamfered had to be ground using an air-powered grinder. This was a difficult operation particularly for sections that were below the water line.
Mesh flooring around piles
STANDARDS AND CODES
There are no Indian standards codes as such for the control of corrosion. The latest editions of the following organizations standards, codes, and guidelines shall be used for the design of corrosion control systems: NACE International (formerly The National Association of Corrosion Engineers) RP0169 Control of External Corrosion on Underground or SubmergedMetallic Piping Systems American Society for Testing and Materials (ASTM) ASTM D512 Standard Test Methods for Chloride Ion in Water ASTM D516 Standard Test Method for Sulfate Ion in Water ASTM G51 Standard Test Method for measuring pH of Soil for Use in Corrosion Testing
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.Bi-directional material is the best option. Scaffolding measures during the application of materials ensures safety and simplifies installation.
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