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Advancements in Ceramic Coating Technology for the Power Generation
Industry
Aldrin Arquillano M.Eng, Research AssociateFurnace Mineral Products Inc. (FMP Coatings)
Industrial processes are operating at higher temperatures and the corrosion rates are accelerating
Conventional organic coatings are exhibiting limited success above 100 oC in immersion service
Next generation hybrid coatings are maximizing temperature resistance These solvent free coatings can withstand temperatures above 200oC while
providing excellent erosion and chemical resistance
ØOperating temperature (wet/dry) service ØIntermittent / Upset exposureØLevels of corrosive liquids/gasesØMicrobial activity (SRB)ØCleaning chemicals/steam cleaningØRapid decompressionØCondensate moistureØCost of failure
High sulphur fuel in the presence of moisture forms sulphuric acidAcidic gas condenses out of the flue gas stream on cooling
Acid condenses at 115 – 160 oC resulting in aggressive corrosion
Coating have had limited success in this environmentThe combination of erosion, high wet temperature and strong acidic
attack pushes the limits of organic coating technology
• Resistant to high temperature (265 oC dry – 200 oC wet)• High wear resistance• Ambient temperature cure• Environmentally friendly, zero VOCs• Chemical resistant (H2SO4, HCl)• Single coat high build application• Spray applied• Rapid return to service
ORGANIC CHEMISTRYContains backbones comprised of chains and/or rings of carbon (plant based) and hydrogen atoms.
INORGANIC CHEMISTRYContains backbones comprised of non carbon containing elements such as silicon (mineral based). Silicon offers extreme thermal stability and temperature resistance
• Ceramic inorganic chemistry for combustion service ranging from 370 to 800 oC• Upon curing the coating forms an amorphous layer that bonds the ceramic matrix to the substrate surface• Limitations
– requires post cure at elevated temperature– Not suitable for immersion service– Difficult to apply– Thin film
Glass Transition Curve
Cross Link Density
Low Tg Higher Tg
Why traditional epoxies fail at high temperature • Low Tg• Low cross link density• High free volume
• Epoxy coatings are organic thermosetting polymers
• Cure by chemical reaction• Reaction between epoxide resin and an amine curing agent
• 3 main components to epoxy coatings(resin, hardener and modifier)
• Primary indicator of temperature resistance is Tg
Type Structure Viscosity Tg
Bisphenol A15,000 cps 175 oC
Bisphenol F5,000 cps 150 oC
NovolacSemi Solid at
Room Temperature200 oC
*Viscosity of water is 1 cps
0
50
100
150
200
250
Bisphenol F Bisphenol A Novolac
Resin Tg (oC)
0102030405060708090
Bisphenol A Bisphenol F Novolac 3.6 f
Temperature at 4,000 cps
0
10
20
30
40
50
60
Bisphenol A Bisphenol F Novolac 3.6 f
Percentage %
Diluent Requirement to Drop to 4,000 cps
• Types of Epoxy Curatives• Polyamide• Aliphatic• Cycloaliphatic• Aromatic
0
50
100
150
200
250
Amide Aliphatic Cycloaliphatic Aromatic
Temperature oC
Hardener Curing Temperature
• Hybridized • Incorporate silicon bonding• High functionality novolac epoxy• Ceramic fillers• Cycloaliphatic amine or aromatic amine
• Include rubber, ceramics, pigment, solvent, fillers, flame retardants, and diluents• Use of solvent or non reactive diluents must be avoided (xylene, benzyl alcohol)• Reactive diluent avoided or only low levels• Fillers must be thermally stable at higher temperature
• Solvency – viscosity reduction• Environmental impact• Sacrifice performance• Will not survive high temperature exposure
Autoclave Testing 96 hrs at 120 oC at vapour pressure
• A 100% solids coating system is defined as a coating that results in no film thickness change during application.
• So how does a formulator of 100% solids coating drive down the viscosity so that the coating can be sprayed or rolled ?
• The trick is the use of a high boiling point solvent (ie, benzyl alcohol) that is volatile but also reacts with the epoxide group of the coating so that the bulk of the solvent remains in the coating system.
• In high temperature systems this approach DOES NOT work• To overcome the need for solvent or diluent, the system must be heated to reduce viscosity
• Two methods• Single leg hot pot• Plural component spray
Characteristic Single Leg (heated) Plural Component (heated)
Ease of Application Requires skilled technician Requires skilled technician
Cost of Equipment $7, 000 USD $30,000 -‐ 50, 000 USD
Solvent consumption Flush every 30 min (dependant of the pot life and exotherm)
Flush at the end of spray
Pot Life Min 30min No limit
Max Material Viscosity 20,000 cps 80,000 cps
Max Temperature 38 oC 65 oC
Lower intercoat porosity
Single coat application reduces therisk of intercoat failure
Improved edge retention> 75 %
Improved pit coverage
Improved adhesive strength
Test Method Description
ASTM D648 Heat Deflection Temperature
ASTM D6137 Sulfuric Acid Resistance of Polymer Linings for Flue Gas Desulfurization Systems
ASTM D5499 Heat Resistance of Polymer Linings for Flue Gas Desulfurization Systems
NACE TM 0174 Laboratory Methods for the Evaluation of Protective Coatings and Lining Materials on Metallic Substrates in Immersion Service
NACE TM 0185 Evaluation of Internal Plastic Coatings for Corrosion Control of Tubular Goods by Autoclave Testing
ASTM 2485 Evaluating Coating for High Temperature Service
CSA Z245.20 Hot Water Soak Test
• Use more aggressive wheel– H 18 (1 Kg, 1000 cycles)
• Result must be less than 100mg to survive high erosive flue gas rates
• Modified version of ASTM G76• 60 m/s aluminum oxide at a 30 mm stand off• Evaluate both 90o and 30o angles
Atlas Cell Testing
Poor wet adhesion
Blisters at thin coating
Hybrid Material
Testing Result
Auotclave at 96 hrs at 160 oC Pass
Taber Abrasion CS-‐18, 1kg, 1000 cycles
< 50 mg
Mix Ratio 4:1 (resin:hardener)
Holiday detectable Yes
Chemical resistance Pass H2SO4, HCl, CH2Cl2 (168 hrs)
Autoclave at 96 hrs at 160 oC
• Hybridization is at the forefront for advanced high temperature development work• Test methods must best simulate the service environment• Heated plural component spray adds performance benefit• Proper high temperature formulations will drive longer term performance
