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Corrosion Protection for Power Plants

MONDAY, JUNE 4, 2018

By Kevin S. Balaban, Advanced Polymer Coatings, Inc.


Whether a power plant is fueled by fossil, oil or renewable sources, its towers, stacks, scrubbers, tanks and other areas prone to corrosion all require protection. To perform at optimal capability, the linings used in these diverse facilities must correlate with the environmental conditions present.

Specifically, in the power generation market, internal lining systems may be designed to protect against abrasion, chemical corrosion and heat — conditions that exist, for example, in the abrasive environment of a coal handling facility or the highly corrosive environment of an absorber/scrubber or in facilities for waste recovery and water treatment.

Figure 1. Power plants have many areas throughout the facility that require high-performance coatings protection from corrosive environments. Photos: courtesy of Advanced Polymer Coatings, inc.

Specialized Protection Needs

Flue gas desulfurization (FGD) units pose a unique challenge in power plants. Scrubbers lined with stainless steel are prone to corrosion. Acid condensation formed during the FGD process — along with abrasion, pit corrosion and chlorides — is a typical source of failure. No two scrubbers are alike. The elevated temperatures, dew point, wet-dry cycles, gas velocity, high sulfate solutions, fluorides and chlorides that may be present will accelerate pitting and crevice corrosion, requiring imminent repairs to the process and structural vessels.

In a wet FGD unit, four areas are prone to corrosion due to constituents of the environment: the 1) absorber/scrubber, 2) outlet duct, 3) mix chamber and 4) stack. Each one of these areas is subjected to different pressures, such as high operating temperatures, highly acidic surroundings and abrasive environments, among others. To protect all of these areas from corrosion, a lining that provides a combination of abrasion, chemical and permeation resistance is needed.

Figure 2. Severe pipe and scrubber corrosion (top) caused by an acidic gas and slurry mixture is protected with a ChemLine lining application (bottom).

Figure 3. Carbon steel stack (top, left) at this power facility has its previous delaminated and corroded lining removed (top, right) and is then re-lined with ChemLine (bottom) to protect against the high-temperature, corrosive environment.

A vinyl ester lining is sometimes applied in these areas at 30 to 60 mils. The disadvantages of this type of lining system are its: 1) high styrene content (extremely flammable and toxic during application and cure), 2) high cure shrinkage (causing cracking and brittleness), 3) sensitivity to atmospheric moisture and temperature, causing the lining to have problems curing when atmospheric conditions are not right, and 4) inability to be repaired in the field and 5) incompatibility with other coatings, making it difficult to bond to dissimilar and already-cured materials. Further, if an applicator adds too much thinner, it causes the lining to lose strength.

Other lining choices include troweled thick-film vinyl esters, spray or troweled flake systems, sprayed-on epoxy, heavy-duty mortar laminate systems with abrasion resistant aggregate and vulcanized rubber. FGD and duct systems can vary depending on system design and fuel source. These conditions can include:

  • SO2
  • Condensing hot H2SO4 (sulfuric acid)
  • Calcium sulfate / lime slurry
  • High temperature /upsetting conditions
  • Highly abrasive gas
  • Substrate movement due to unit cycling/vibration

Figure 4. Flue gas attacks the alloy construction of reheater tubes (top), causing corrosion in this FGD system, but after coating with ChemLine (bottom), the tubes now operate at peak performance.

Figure 5. Carbon steel booster fans in an FGD stack exhibit severe corrosion (top), but after coating the fan blades with ChemLine, the unit is now protected (bottom).

ONE LINING, MULTIPLE CONDITIONS

High-build vinyl ester linings are a traditional choice for power facility ductwork, as their low permeability prevents the absorption of hot condensing flue gases that attack the lining substrate.The permeation rate of Chemline, from Advanced Polymer Coatings, Inc. (Avon, Ohio, USA), is 0.0000 grams per square foot per 7 days per inch of thickness. ChemLine offers a thin film option at 12 to 14 mils that provides excellent resistance to chemicals, hot flue gas conditions and extreme abrasion. It also offers flexibility to handle substrate movement not found in vinyl esters.

*Claims or positions expressed by sponsoring authors do not necessarily reflect the views of TPC, PaintSquare or its editors.

ABOUT THE AUTHOR
Kevin S. Balaban, Advanced Polymer Coatings, Inc.

Kevin S. Balaban, global industrial sales manager at APC, handles ChemLine coating sales and business development for industrial markets that include petroleum and refining, chemical, power, manufacturing, pipelines, tank storage and secondary containment. He has 25 years of experience in various leadership roles, encompassing industrial sales, business development, marketing and product management.

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