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Coatings  basics corrosion

Coatings basics corrosion



Coatings basics corrosion

Coatings basics corrosion



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    Coatings  basics corrosion Coatings basics corrosion Presentation Transcript

    • Corrosion Control
    • Corrosion Control Methods• Better Design• Better Selection of Materials• Corrosion Control by Coatings• Corrosion Control by Inhibitors• Corrosion Control by Cathodic Protection• Corrosion Control by Anodic Protection
    • Factors affecting the service Life
    • Better Design
    • Weld Design
    • AvoidCrevices
    • Avoid Erosion Corrosion
    • Better Material Selection• Material Selection Criteria• Lowest Corrosion rate• Also falls within the project cost• If there is choice to select between steel and SS, you can better select SS• But if the choice is to select only steel, then one has to make thorough investigations of various steels and find the best for application – based upon the chemistry of the steel
    • Protection by Coatings
    • Protection by Coatings Classification of Coatings Metallic / Ceramic/Organic Room Temperature Application/ High Temperature Application Zn ( Galvanization), Cr, Sn, Ni, CdAluminising, Al-Cr, Nitriding, carborizing
    • Method of Application Hot Dip Method Slurry method Electroplating/Electroless PlatingLiquid route ( Cyanide bath)/Sol-gel PVD/CVD Thermal Spray / Laser Coatings by Spray – paint spray
    • Paint Coatings• Though appears simplest method of Corrosion Control, actually not so in practice.• It is an art as well as science.• Requires good knowledge of paint formulations, paint selection, application skill, suitable surface preparation method & experience and inspection methods.
    • Why paint Coatings ?• Aesthetics• Corrosion Protection• Both
    • Paint System• Surface Preparation• Primer• Intermediate layer• Top layer•A technician is required to properly carry out above jobs.•An inspector / supervisor is required to continually monitor the requirement as per specifications.
    • Main Properties of a Coating• The coating material should be an effective electrical insulator• It can be applied with no breaks• The coating must be strong enough to resist the impact of sharp objects.• It constitutes initially a perfect film which remains so with time.
    • Surface Preparation• Surface Cleaning – Conversion Coatings – Blasting • Dry • Hydroblasting
    • Paint Application• Brush• Rollers• Air Spray• Airless Spray
    • Coating Composition• Binder ( Resin)• Solvent• Pigment• Additives
    • Pigments• Several Functions as part of Coating – Provide colour & Opacity • TiO2, C or lamp black – Reinforce the film structurally • Iron oxides – Corrosion resistance • Zn ( Galvanically) – Talc & mica act as extenders, reduce permeability through film as plate like particles block permeation. – Lead chromate as inhibitive pigment
    • Role of PigmentPigment InhibitiveBarrier Coating Primer Organic Rich Coatings Inorganic rich coating
    • Organic Zinc Rich Coatings• They utilize an organic resin rather than an inorganic silicate binder for film formation.• They protect steel galvanically as well as by barrier protection but do not provide a high level of galvanic protection as do inorganic Zn rich coatings.• They are formed by simple solvent evaporation or by chemical reaction of components.• Film properties of these coatings are similar to that of free zinc organic coatings.• Organic Zn Coatings do not require high level surface cleanliness while inorganic Zn coating require the best cleaned surface.
    • Inorganic Zn-rich PrimerOrganic Zn-rich primers
    • Additives• Trace or small quantities of these help in modifying various properties: – Phenylmurcury, Zinc, Cuprous compounds act as mild inhibitors – Co and Mn Napthanates - help in drying – ZnO - protection of resin from heat and Sun
    • What is required from a Paint Coating• Good Adhesion• Flexibility• Impact Resistance• Resistance to environment – Chemical – Moisture – Sunlight / Rains
    • Types of Coatings• Conventional – Lacquers, solutions of synthetic resins ( vinyl chloride, rubber and acrylic) – Water emulsion (latex) Coatings ( acrylics and Vinyls) – Oil based coatings – Epoxy Coatings – Coal tar Epoxy coatings – Poly-urethanes – Polyester and Vinyl ester coatings – Organic Zn rich Coatings• Special – Solvent Less Coatings – Fiber Reinforced coatings
    • Lacquers• Lacquers are solutions of natural resins ( Shellac or bituminous materials) or synthetic resins ( vinyls, chlorinated rubber and acrylics).• Upon application, solvent evaporates and the resin deposits unchanged.• Films have good water and chemical resistance but poor solvent and heat resistance.• Require abrasive blast cleaning.• Applied in Multiple coats and easy to topcoats for repair.• Have Good gloss Retention and resistance to weathering. Advantages Limitaions Rapid Drying & Recoating High in VOC Good General Chemical Resistance Poor Solvent Resistance Good in water immersion Low film build up Good gloss Retention Blasted surface is necessary Good Durability Occasional poor adherence
    • Water Emulsion Latex• Latex coatings are being successfully used to coat wood and masonry structures.• Relatively porous nature of structure allows water vapour to pass through them. Advantages Limitations Reduced level of VOC Limited Durability Easy to apply, topcoat & repair Poor chemical resistance Fast to dry for recoating Poor wetting of surface Excellent Flexibility Poor immersion service Low Cost Best cure above 50 C.
    • Oil Based Coatings• Coatings based upon drying oil ( linseed oil, tung, soyabean, fish oil).• Cure by reaction with oxygen.• Though complete dry less than in one day, complete curing takes much longer.• Alkyd coatings use resin formed by the reaction of polyhydric alcohols ( glycerin) and polybasic acid ( phthalic acid) followed by modification with drying oils. These cure much faster than unmodified alkyds..• Silicon alkyd coatings were developed by modifying alkyd resin with silicon ( 30%) to provide greater gloss retention.• Epoxy ester coatings are another modification of drying oils to improve performance, particularly chemical resistance.• Uralkyd coatings are formed with polyurethane. These coatings are hard.
    • Epoxy Coatings• The Most Common two component thermosetting product.• An epoxy resin is based on a reaction product of phenols, commonly bisphenol F or Cresol with epichloridehydrin.• Available in solvent free, with solvent or water containing formulations.• The two components are called base and the curing agent. Latter is used to polymerise the epoxy resin which has major influence on the mechanical and chemical resistance properties. The most common curing agents are aliphatic amines, ketamines and polyamides.• Epoxy coatings bond well to the abrasive cleaned steel and clean concrete.Their films are hard and relatively inflexible. They chalk in sunlight.
    • Epoxy CoatingsWe make the prepolymer using bisphenol A andepichlorohydrin Bisphenol A Epichlorohydrin Diepoxy molecule
    • Polyurethane Coatings R-N = C = O + OH--R = R- NH- C - O -R• Very important Class of Coatings• Urethanes are perhaps the most common materials used in our day to day life.• Soft, flexible to rigid materials are availbale.
    • Polyester and Vinyl ester Coatings• Unsaturated polyester and vinyl ester thermosetting resins are used as base for a useful group for a high performance corrosion resistant lining for steel, concrete and other surfaces• Polyesters and vinyls contain unsaturated groups which are reacted with unsaturated monomers such as styrene.The combination of resin and monomer forms a relatively low viscosity material to which when added some catalysts such as peroxides accelerate curing.• A great skill is required to ensure proper propotionating and mixing – Limited pot life – Blast surface required when used as primer. – More expensive than epoxies.• To the final lining product, one can add reinforcements and fillers to minimise the effect of shrinkage and enhance properties such as lowering coefficient of friction and increasing tensile strength and decrease permeation.• Polyesters and vinyls are applied in large thicknesses from 500 um to 5 mm.
    • Natural and Synthetic Rubber Linings• Natural and synthetic rubber linings are used in such industries as steel, chemical, paper, plating, mining, agriculture and power• The physical properties of these steel linings allow them to protect steel from erosion, corrosion, abrasion and chemical attack.• These linings are applied to various types of equipments such as flue gas desulphurisation systems, pipe, tanks, railway tank cars, rolls and pulleys.• Typical thickness of Rubber linings are from 3.2 mm to 6.4 mm.• Surface should be blast cleaned SA21/2 with a profile of 40-50 um.• The surface before linings must be primed with suitable primer.
    • - CH - CH2- Epoxy Chlorinated rubber Polyester Coating --- CH -- CH -- O = C - OCH2 - - CH3 AcrylateVinyl Acetate Urethane R-N = C = O + OH--R R- NH- C - O -R
    • Paint Application1. Brush or Rollars2. Spray • Air Spray • Airless Spray • Electrostatic Spray
    • Airless, Theory of Operation• Airless spray atomization 2000+ psi fluid pressure - hydraulic force through a cats eye shaped orifice• 2000+ psi fluid pressure• Fastest and heaviest spray Transfer efficiency = 50 - 60% finish and is measured in liters per minutes• Transfer efficiency = 50-60%• Protective coatings Click to see spray 36
    • Transfer Efficiency• Transfer efficiency (TE) = (paint deposited on a part)/(total paint sprayed)• TE = (Wp/Ws) x 100% Wp = Weight of wet coating on the part Ws = Weight of liquid coating sprayed
    • Electrostatic Technology
    • High Performance Coatings1. One those which are functional specific2. Can be applied in highly aggressive environment.3. Have high Corrosion resistance4. High Erosion & abrasion resistance5. Can dry very fast6. Can give large thickness in one coat
    • Solventless SystemsCan achieve very high thickness in one coat Can have Drying time of a few minutes Life can further enhanced by addition of glassfalkes
    • Fibreglass Reinforced Linings• Fibergalss-reinforced plastic (FRP) linings are unstaurated polyester and vinyl ester thermosetting resin linings into which fibre glass are incorporated to optimize the lining performance.• They are commonly used to control the internal corrosion of above ground petroleum storage tank bottoms.• The main reinforcement used with polyester and vinyl ester resin liner are E glass mat and 250 um glass veil ( very thin fibre glass mat) which has electrical properties, strength and durability appropriate for most applications.• C glass mat is chemical resistant, e.g. resistant to most acids. A 3000g/m2 is sometimes used instead of choopede strand mat.
    • Moisture PenetrationGlass Flakes Coating Substrate Substrate
    • Offshore StructuresGlass Flake ReinforcedPolyester Coating to achieve750um in one coat
    • Application• Underwater: – Brushes - Using vigorous circular motion. – Underwater pump with round brush - using vigorous circular motion
    • • Once we have made diepoxy prepolymers, we tie them all together by adding a diamine.
    • How Epoxies Work• The well known adhesion of epoxies is due to the strong polar bonds it forms with the surfaces it comes in contact with.• On dry surfaces the bond between the surface and the epoxy displaces the air, which is a fluid.• The same is true underwater. As on dry surfaces, the polar bond attraction is strong enough to displace the fluid, in this case the water, and produce an strong bond even underwater.• Thus, painting underwater is, in theory, no different that painting above the water. The cross linking reaction of epoxies should be independent of the surrounding environment.
    • POWDER COATINGS• Type I Thermoplastic - are high molecular weight products that melt, flow and form a film without change in their chemical composition. Because they are difficult to grind they are often applied in fluidized beds and used in thick films. : polyethylene, polypropylene, PVC, nylon.• Type 2 Thermosets - are lower molecular weight polymers that cross link during heat curing to form higher molecular weight. They can be ground finer and thus applied in thinner films 25-200 um. They chalk in presence of UV light.• FBE is one of the best known thermoset Coatings used in large applications for external and internal pipelines corrosion protection.• Application methods : Fluidized bed, electrostatic spray, hot flocking and thermal spray.
    • Fluoroelastomeric Coatings• Fluoroelastomeric coatings are among the most expensive and highest performance coating materials in present Day.• Application, surface finishing, material mixing are of paramount importance• Fluoroelastomeric coatings are chemical resistant coatings that can withstand elevated temperatures and attack by acids and alkalies, hydrocarbons, gases and solvents and many harsh industrial chemicals.• They are generally two component catalysed systems that cure at room temperature.• Physical properties can be controlled by varying the amount of catalysts.• They are commonly used as heat and acid resistant linings in power station flues and duct work. And also in tanks, sumps, ditches, hazardous waste dikes and immersion zones.
    • Fluoropolymer Bonds are Less Likely to Break The C-F bond is one of the strongest known (PVDF shown below)
    • Fluorine Content of PVDF
    • Chemical Spot Test PVDF Polyester
    • Tapes & Wrappers• TAPES are finally prepared coating material ready to apply onsite.• They may be either thermoplastic or felt impregnated with petrolatum or petroleum wax.• Success of tapes depends upon the application. The most important problem is the improper overlapping that causes gaps where shielding corrosion may take place.• The most common application of tapes is for immediate repair of underground pipelines.• One of the failure areas of tapes is in above ground araes such as soil to air pipe transition zones• Experienced tape applicators or especially with machine wrapping one can eliminate failure problems.
    • Thermal Spray Coatings• The most latest and easy to apply and provide much longer life.• Flame spray, Arc Spray, Detonation Gun or Plasma Spray guns are used.• They are also called hybrid systems with internal metal coating with a top seal coating of epoxy or PU.• Life of such coatings is 25- 50 years.
    • Various Thermal Spray Systems Flame Arc HVOF Plasma
    • Actual Application Flame SprayThermal Spray by Robots
    • Summary• Paint Coating is one of the most effective and known methods of corrosion protection at the surface.• To get an excellent corrosion protection, several factors which include, proper surface preparation, correct application technique, suitable environmental conditions, inspection during surface preparation and application are required.• Paint selection is very important. Depending upon the environment, a suitable system is selected.• Most modern paint coating systems such as Floroelastomers, glass flake systems are used for selective applications are now readily available.