Flue Gas Corrosion Glossary: 40 Terms Engineers Use

Flue Gas Corrosion Glossary: Key Points

• A polymer-alloy-ceramic coating is Polylloy Coatings' family name for its hybrid coatings; only FlueGard®-455CHT, KilnGard®-600SCW and WearGard®-625S are published as ceramic or nano-ceramic, so specify by grade code.
• A heat cured coating is applied at ambient temperature and reaches final properties when heated in service; for Polylloy's heat-cured grades, final heat cured activation is completed during start-up using process heat, and CorrosionGard®-160S is the ambient-cure exception.
• Polylloy bulletins specify SSPC-SP10 / NACE No. 2 near-white metal blast with a surface profile above 3 mils (75 µm).
• The acid dew point, typically 120 to 160 °C in cement flue gas, is the term behind much of the corrosion in baghouses, ducts and stacks.
• The 40 terms sit in six themes, from chemistry and equipment to testing, design and cost, each defined in one or two sentences with a link to the page covering it in depth.

A polymer-alloy-ceramic coating is Polylloy Coatings' family name for its hybrid coating systems that protect steel in hot, corrosive gas; chemistry differs by grade, and only some grades are ceramic. This flue gas corrosion glossary defines it and 39 more terms, from acid dew point to heat cured activation and SSPC-SP10 blasting.

What a Flue Gas Corrosion Glossary Covers

Flue gas corrosion is attack on steel in ducts, dust collectors, scrubbers, fans and stacks by acids, chlorides and deposits from combustion and process gases, especially where metal runs below the acid dew point.

How to Use This Glossary

Each term gets one or two sentences and a link to its in-depth page. Terms marked Polylloy usage are company terminology, not industry standards.

Flue Gas Chemistry and Corrosion Mechanism Terms

Chemistry and mechanism terms describe how acids, chlorides and deposits attack steel in the gas path.

Acid Dew Point

Acid dew point is the temperature below which acid vapors in flue gas condense on a surface. In cement plant flue gas it is typically 120 to 160 °C (248 to 320 °F), set by sulfur trioxide and moisture (International Cement Review, May 2026); see the acid dew point corrosion warning signs.

Sulfur Trioxide (SO3)

Sulfur trioxide (SO3) is the oxide formed when part of the sulfur dioxide (SO2) in flue gas oxidizes. It combines with water vapor to form sulfuric acid and raises the acid dew point.

Sulfuric Acid Condensate

Sulfuric acid condensate is the liquid sulfuric acid (H2SO4) film that forms wherever steel falls below the acid dew point. Its strength varies from plant to plant.

Hydrogen Chloride (HCl) and Chloride Attack

Hydrogen chloride (HCl) is an acid gas that forms hydrochloric acid condensate and chloride-bearing deposits. Chlorides, more common with alternative and waste-derived fuels, break down stainless steel's passive film.

Alkaline Dust Buffering

Alkaline dust buffering is the partial neutralization of acid condensate by alkaline compounds in cement dust. It occurs on a baghouse's dirty-gas side and is largely absent on the clean side.

Under-Deposit Corrosion

Under-deposit corrosion is localized attack beneath retained dust or ash. Polylloy's technical paper traces it from deposition through cooling at shutdown, moisture uptake and salt dissolution; see the baghouse corrosion maintenance checklist.

Pitting and Crevice Corrosion

Pitting and crevice corrosion are localized attack where stainless steel's passive film breaks down in wet chloride service, as pits on open surfaces or in shielded gaps at overlaps, fasteners and deposits. See why 316 stainless corrodes in flue gas.

Chloride Stress Corrosion Cracking (SCC)

Chloride stress corrosion cracking (SCC) is cracking of susceptible austenitic stainless steel exposed to chlorides under tensile stress, including residual welding stress.

Erosion-Corrosion

Erosion-corrosion is metal loss in which particle impact or flow strips the protective corrosion layer while acid or moisture attacks the fresh steel, so each process speeds up the other. See abrasion-resistant coating suppliers.

Flue Gas Path Equipment Terms

Equipment terms name the parts of the flue gas path where corrosion is most often found.

Baghouse (Fabric Filter)

A baghouse is a dust collector that filters flue gas through fabric bags. Its dirty-gas side, tubesheet, clean air plenum and hoppers each corrode differently; see baghouse corrosion protection options.

Clean Air Plenum

The clean air plenum is the baghouse compartment above the tubesheet that carries filtered gas to the outlet. Lacking alkaline dust buffering, it is often the first site of acid damage.

Electrostatic Precipitator (ESP)

An electrostatic precipitator (ESP) is a dust collector that charges particles and collects them on plates. Its casing, hoppers and outlet ducts face the same acid condensation risk as a baghouse; see air pollution control corrosion protection.

Flue Gas Desulfurization (FGD) Scrubber

A flue gas desulfurization (FGD) scrubber is the absorber that removes sulfur dioxide from flue gas, usually with a wet slurry. It creates saturated, acidic and chloride-bearing conditions in the absorber, outlet ducts and stack; see FGD corrosion protection.

Induced Draft (ID) Fan

An induced draft (ID) fan pulls flue gas through the system. Its housing and impeller see acid gas, hydrogen fluoride (HF) in some cement service and high-velocity dust together; see ID fan housing protection options.

Steel Stack

A steel stack is the chimney at the end of the flue gas path, often its coldest stage, where gas can cross the acid dew point and liners or insulation can hide shell corrosion; see industrial chimney corrosion protection.

Kiln Shell

A kiln shell is the rotating steel cylinder of a cement or lime kiln. Beneath the refractory, corrosion stays hidden until a thickness survey or hot spot reveals it; see kiln shell corrosion protection.

Refractory Lining

A refractory lining is the brick or castable layer that insulates steel from process heat. It does not stop corrosive gases reaching the steel, and a coating does not replace it; see corrosion behind refractory linings.

Coating Chemistry and Material Terms

Coating chemistry terms separate Polylloy's grade families from conventional linings.

Protected Carbon Steel

Protected carbon steel is carbon steel equipment shielded by an engineered coating that isolates it from hot, corrosive gas and condensate. It is weighed against 316 stainless steel in carbon steel vs stainless steel.

Polymer-Alloy-Ceramic Coating

Polymer-alloy-ceramic (Polylloy usage) is Polylloy Coatings' family name for its hybrid coating systems, engineered for chemical resistance, thermal stability and abrasion protection, with chemistry that differs by grade. Only FlueGard-455CHT (ceramic), KilnGard-600SCW and WearGard-625S (nano-ceramic) are published as ceramic, so specify by code from the Polylloy coating grades by temperature and gas chemistry.

Alloy-Inorganic-Organic Hybrid

Alloy-inorganic-organic hybrid (Polylloy usage) describes a coating combining alloy, inorganic and organic components in one system, which Polylloy describes as fundamentally different from glass-filled epoxy, novolac and phenolic coatings. FlueGard-225SQC, a two-component polymeric alloy rated to 225 °C (437 °F), is the example; see anti-corrosion coating types.

Nano-Ceramic Coating

A nano-ceramic coating is a ceramic coating built from nanoscale ceramic phases. Polylloy's KilnGard-600SCW (to 600 °C, beneath refractory) and WearGard-625S (to 625 °C, hot abrasion) are two-component nano-ceramic grades; see industrial ceramic coatings for steel.

Novolac Epoxy

Novolac epoxy is a coating based on epoxy novolac resin, which has more reactive sites per molecule than standard bisphenol-A epoxy. That gives a higher-crosslink lining for acid service within its product rating; see novolac, vinyl ester and hybrid coatings.

Glass-Flake Vinyl Ester

Glass-flake vinyl ester is a vinyl ester resin lining filled with glass flakes, used for wet acid and scrubber service within the product data sheet's rating.

Silicone Heat-Resistant Coating

A silicone heat-resistant coating is a thin silicone or silicone-modified paint, often aluminum-pigmented, rated for dry exterior heat rather than for acidic gas inside equipment. See high temperature coatings above 400 °C.

Surface Preparation, Application and Cure Terms

Preparation and cure terms set what a specification must state before work starts.

SSPC-SP10 / NACE No. 2 Near-White Metal Blast

SSPC-SP10 / NACE No. 2 is the joint Society for Protective Coatings and NACE surface preparation standard for near-white metal abrasive blast cleaning. Every Polylloy bulletin specifies it; see the coating outage planning steps.

Surface Profile

Surface profile is the peak-to-valley depth of the anchor pattern left by abrasive blasting. Polylloy bulletins require more than 3 mils (75 µm).

Dry Film Thickness (DFT)

Dry film thickness (DFT) is the thickness of the dried coating film on the steel, checked against the grade bulletin range. Examples are 15 to 25 mils single coat for KilnGard-600SCW and 16 to 20 mils over two coats for FlueGard-455CHT.

Heat Cured Coating

A heat cured coating is applied at ambient temperature and reaches its final properties when heated in service. For Polylloy's heat-cured grades, the heat activates chemical bonding with the steel and the coating's internal bonding.

Heat Cured Activation

Heat cured activation (Polylloy usage) is Polylloy's term for completing the cure of its heat-cured grades in service. Final heat cured activation is completed during start-up using process heat.

Ambient Cure

Ambient cure means a coating reaches its final properties at room temperature without heat. CorrosionGard-160S is Polylloy's ambient-cure grade, and its 160 °C (320 °F) figure is a service limit, not a cure temperature; see chemical service coating suppliers.

Coating Testing, Inspection and Failure Terms

Testing and failure terms describe how a coating is checked and how its failures are read.

Holiday (Continuity) Test

A holiday (continuity) test passes a voltage probe over the coating to find pinholes and other through-film defects, on Polylloy's heat-cured grades before final cure. Polylloy's 56 % sulfuric acid report tested at 2.0 kV on a 20 mil film.

Pull-Off Adhesion (ASTM D4541)

Pull-off adhesion is the tensile stress needed to pull a bonded dolly off the coated steel, reported in psi under ASTM D4541. Polylloy bulletins list above 3,000 psi for FlueGard-225SQC and above 1,000 psi for WearGard-625S; see the coating standards and tests to ask for.

Taber Abrasion (ASTM D4060)

Taber abrasion is the mass a coating loses under abrasive wheels, reported in mg after 1,000 cycles with CS-17 wheels and a 1 kg load under ASTM D4060. Lower is better, for example 20 mg for FlueGard-455CHT and below 150 mg for FlueGard-425S.

Immersion Test

An immersion test exposes a coated panel to a liquid chemical for a set time, then checks the film. Polylloy's own six-month FlueGard-225SQC test in 56 % sulfuric acid at 60 °C is reported in the sulfuric acid immersion test results.

Electrochemical Impedance Spectroscopy (EIS)

Electrochemical impedance spectroscopy (EIS) measures how strongly a coating resists water and ions. A log impedance modulus above 9 at 0.1 Hz indicates a low-permeability barrier.

Undercutting Corrosion

Undercutting corrosion is corrosion that spreads beneath a coating from a defect or edge, lifting the film from the steel. Polylloy laboratory and field testing observed it in conventional high-temperature coatings; see how to diagnose coating failures in hot flue gas.

Delamination

Delamination is loss of adhesion between a coating and the steel, or between coats, so the film lifts away. Diagnosis examines the exposed steel and the back of the lifted flake.

Design and Cost Terms for Flue Gas Equipment

Design and cost terms frame the protection choice.

Service Limit

A service limit is the published maximum operating temperature of a coating grade, matched against normal and excursion temperatures. FlueGard-425S, for example, is rated to 425 °C (797 °F) with peaks to 500 °C.

Corrosion Allowance

A corrosion allowance is extra wall thickness added beyond what strength requires, intended to be consumed by corrosion over the design life. See corrosion allowance or coating design options.

Lifecycle Cost

Lifecycle cost is the total cost of protection over a stated period, adding maintenance, downtime and replacement to material and installed cost. Pricing is project-specific; see industrial coating project cost.

How to Use Flue Gas Corrosion Terms in a Coating Specification

Flue gas corrosion terms are most useful as specification lines.

Putting the Glossary to Work

A specification that names the grade code, service limit, SSPC-SP10 / NACE No. 2 with its profile, DFT range, holiday test and cure route leaves fewer gaps than one naming a product family. Polylloy formulates, supplies, specifies and supervises; certified partners apply its coatings.

Grade families are summarized under Polylloy corrosion protection solutions. To match terms to a duty, request a coating evaluation with equipment type, coated area, operating conditions (temperature, gas chemistry, abrasion), location and outage timing.

FAQs

What is a Polymer Alloy Ceramic Coating?

Polymer-alloy-ceramic is Polylloy Coatings' family name for its hybrid coating systems, engineered for chemical resistance, thermal stability and abrasion protection, with chemistry that differs by grade. Not every grade is ceramic: FlueGard-455CHT, KilnGard-600SCW and WearGard-625S are published as ceramic or nano-ceramic, so specify by grade code.

What is a Heat Cured Coating and Why Does It Need Heat?

A heat cured coating is applied at ambient temperature and reaches its final properties when heated in service. For Polylloy's heat-cured grades, heat activates the chemical bonding with the steel and the coating's internal bonding. Final heat cured activation is completed during start-up using process heat.

What Surface Preparation Standard is Required for Flue Gas Coatings?

Polylloy bulletins specify abrasive blasting to SSPC-SP10 / NACE No. 2 near-white metal with a surface profile above 3 mils (75 µm). A site that cannot blast to that standard is not a fit. Other manufacturers set their own requirements, so check each product data sheet before writing a specification.

What is the Acid Dew Point in Flue Gas?

The acid dew point is the temperature below which acid vapors in flue gas condense on a surface. In cement plant flue gas it is typically 120 to 160 °C, depending on sulfur trioxide concentration and moisture. Steel running below it at cold spots, leaks or shutdowns collects acid condensate and corrodes.

What is the Difference Between Ambient Cure and Heat Cure Coatings?

An ambient cure coating reaches final properties at room temperature, while a heat cure coating needs heat after application. Among Polylloy grades, CorrosionGard-160S is the ambient-cure exception, with a 160 °C service limit. The other grades are heat-cured, with final heat cured activation completed during start-up using process heat.

What Does a Holiday Test Check on a Coating?

A holiday test checks a coating for pinholes and other through-film defects by passing a voltage probe over the surface; a defect lets current reach the steel. On Polylloy's heat-cured grades it runs before final cure so defects can be recoated. Polylloy's 56 % sulfuric acid report tested a 20 mil film at 2.0 kV.