Chemical Plant Corrosion Protection: Structures, Vessels, Ducts and Stacks

Chemical Plant Corrosion: Key Points

• Chemical plant corrosion protection is decided zone by zone: structures and vessels, tank interiors, and ducts and stacks carrying acid gas each need a different answer.
• CorrosionGard®-160S is a two-component, ambient-cure coating rated to 160 °C (320 °F); its bulletin lists steel structures, equipment, storage tanks and pressure vessels handling corrosive gases and chemicals.
• Its bulletin reports one-week immersion weight gain below 0.5 % in 10 % hydrochloric, 54 % phosphoric and 10 % sulfuric acid and in water; other chemicals need evaluation.
• Ducts, scrubbers and stacks carrying acid gas move to flue gas grades such as FlueGard®-225SQC (225 °C) or StackGard®-255SQW (255 °C), heat-cured at start-up.
• Where steel is dry and sees no acid fume, splash, condensate or chemical contact, a conventional coating is adequate.
• Certified partners apply the coatings; Polylloy formulates, supplies, specifies, trains and supervises.

Chemical plant corrosion protection matches the coating to each zone. CorrosionGard-160S, an ambient-cure coating rated to 160 °C (320 °F), covers structural steel, process vessels and tanks exposed to acid fume, splash or chemicals; FlueGard-225SQC or StackGard-255SQW covers ducts and stacks carrying acid gas. Where exposure is mild, a conventional coating is enough.

Chemical plant corrosion protection is the selection of coatings, linings or alloys that keep the structures, process vessels, storage tanks, ducts and stacks of a chemical processing plant from attack by acid fume, chemical splash, condensate and immersion, matched to each zone's chemistry and temperature.

Chemical Plant Corrosion Challenges Matched to Protection

Chemical plant corrosion protection starts with a map of zones, because each zone sees a different exposure and fails in a different way. The table sets out six typical zones.

Polylloy's company profile lists vessels, tanks, process equipment and gas-handling assets for petrochemical and chemical plants. No bulletin prints "chemical plant," so each grade is matched to the exposure it documents.

How Acid Fume, Splash, Condensate and Immersion Attack Chemical Plant Steel

Acid fume, splash, condensate and immersion attack chemical plant steel by different routes, so each needs its own line in the specification.

Four Exposure Types, Four Different Specifications

The four exposure types are:

• Acid fume: vapor that condenses on cooler steel.
• Splash and spill: intermittent wetting and drying.
• Condensate: acid forming where gas-path steel runs below its dew point.
• Immersion: continuous contact in tanks and vessels.

Fume and splash concentrate acid as films dry, condensate collects at cold spots, flanges and stiffeners, and immersion pushes chemicals through any permeable film. Immersion data does not automatically cover fume exposure, or the reverse, so the exposure type is written into the specification for each zone.

Contamination Under the Film

The CorrosionGard-160S bulletin notes that airborne particles reaching the blasted surface swell by osmosis under a coating and cause blisters, cracks and delamination. The salt contamination mechanism is covered in more depth in the list of severe chemical service coating suppliers.

CorrosionGard-160S for Structural Steel and Platforms in Chemical Plants

CorrosionGard-160S is the Polylloy grade for structural steel and platforms that see fume, splash or chemical contact.

What the Bulletin Lists

CorrosionGard-160S is a two-component, single-layer, ambient-cure coating for hot structural steel, rated to 160 °C (320 °F). Its bulletin lists internal and external surfaces of steel structures and equipment, describes resistance to severe dust abrasion, and states zero volatile organic compounds (VOC) as supplied.

Bulletin properties include Shore D hardness above 80, Taber abrasion below 100 mg and adhesion to steel above 2,000 psi (ASTM International method D4541). It also reports 0 mm corrosion after more than 24 months of acid and salt spray weathering. The family is described on the CorrosionGard ambient-cure coatings page.

Ambient cure suits steel that never sees process heat. The coating can be inspected and repaired before the structure goes into service.

Acid Fume Exposure, Stated Honestly

The bulletin gives immersion data in hydrochloric, phosphoric and sulfuric acid. Fume and splash exposure from other chemicals, such as organic acids, solvents, oxidizers or caustics, is confirmed by Polylloy's technical team for each medium.

Process Vessels and Storage Tanks in a Chemical Plant

Process vessels and storage tanks bring continuous chemical contact, which is where immersion data counts.

Vessels Handling Corrosive Gases and Chemicals

The CorrosionGard-160S bulletin lists storage tanks and pressure vessels that handle corrosive gases and chemicals, and the brochure rates it for immersion. One-week immersion weight gain is below 0.5 % in 10 % hydrochloric acid (HCl), 54 % phosphoric acid (H3PO4), 10 % sulfuric acid (H2SO4) and water (ASTM D471). Untested media, strengths and temperatures need evaluation.

Tank Linings: Summary and Link

The choice between a hybrid lining and conventional epoxy, including where epoxy is the right answer, is set out in the chemical tank lining comparison.

For vessels being designed in 316 stainless, protected carbon steel may offer a cost-effective alternative to stainless steel where the coating is suitable for the specified service conditions. The trade-offs are covered in carbon steel vs stainless steel.

Ducts, Scrubbers and Stacks Carrying Acid Gas in Chemical Plants

Ducts, scrubbers and stacks carrying acid gas sit outside the CorrosionGard-160S envelope and move to the flue gas grades.

Where the Gas Path Needs a Flue Gas Grade

Gas-handling equipment above 160 °C, or carrying acid gas from a boiler, incinerator or other combustion source on site, moves to the flue gas grades. The gas chemistry is matched to each bulletin's resistance list, and the families are described on the FlueGard flue gas coatings page.

FlueGard-225SQC is a two-component polymeric alloy rated to 225 °C (437 °F). It resists sulfur trioxide and sulfur dioxide (SO3, SO2), HCl, carbon dioxide (CO2), hydrogen fluoride (HF) and nitrogen oxides (NOx), and it is immersion-rated.

One-week immersion weight gain is below 1.0 % in 37 % HCl, below 0.5 % in 54 % H3PO4, below 0.5 % in 36 % H2SO4 and below 1.0 % in 3 % HF.

Polylloy's own six-month test in 56 % sulfuric acid at 60 °C showed no observed deterioration of FlueGard-225SQC. It was not independent and covered one panel and one condition, as the 56% sulfuric acid immersion test page explains.

Stacks and Chimneys

StackGard-255SQW is rated to 255 °C (491 °F) and is described by its bulletin as a high temperature corrosion protection system for chimneys of industrial plants, with ducts and fans. Lining options from other makers appear in the list of stack and chimney lining suppliers.

For both flue gas grades, final heat cured activation is completed during start-up using process heat. CorrosionGard-160S is the ambient-cure exception.

When a Conventional Coating is Enough in a Chemical Plant

A conventional coating is enough wherever severe exposure is absent, and Polylloy grades are not proposed there.

Mild Service is Not a Fit

Dry indoor steel, light atmospheric exposure and steel with no acid fume, splash, condensate or chemical contact are adequately served by a conventional coating system. Polylloy treats that service as outside its fit. Other limits apply as well:

• CorrosionGard-160S stops at 160 °C.
• A coating does not replace acid brick or refractory.
• Steel that cannot be blasted to SSPC-SP10, the Society for Protective Coatings (SSPC) near-white standard, with a profile above 3 mils (75 µm) is not a fit.
• Small, complex or inaccessible parts may suit 316 or a higher alloy.

How Polylloy Supports Chemical Plant Engineers on a Specification

Polylloy supports chemical plant engineers by turning plant data into a written specification per zone.

Specification Inputs per Zone

The inputs for each zone are chemicals and concentrations, exposure type, normal and peak steel temperature, cleaning and steam-out cycles, previous coating failures, access and the outage window. Polylloy reviews the data, recommends a grade per zone, writes the specification and supervises. Certified partners in a network of 15 partners across 22 countries prepare the steel and apply the coating.

Outcomes for the Engineer

The engineer receives a zone-by-zone specification with grade, service limit, surface preparation and inspection hold points that can be defended at review. Performance detail comes from completed projects and from Polylloy's technical team for the project under review.

Choosing Corrosion Protection for a Chemical Plant Zone by Zone

Choosing corrosion protection for a chemical plant follows a short decision path:

• Mild, dry exposure: conventional coating.
• Structures, platforms and vessels to 160 °C with fume, splash or chemical contact: CorrosionGard-160S, confirmed per medium.
• Tank interiors: compare hybrid and epoxy linings.
• Acid gas ducts and scrubbers to 225 °C: FlueGard-225SQC.
• Stacks to 255 °C: StackGard-255SQW.
• Beyond coating limits: refractory, acid brick or alloy.

To build a specification for your plant, request a coating evaluation with equipment type and zone, coated area, chemicals and concentrations, exposure type, normal and peak temperatures, location and outage timing.

FAQs

Which Chemical Plant Zones Need a Severe-Service Coating?

Zones where acid fume, chemical splash, condensate or immersion reach the steel: structures and platforms near process units, process and pressure vessels, storage tank interiors, and ducts, scrubbers and stacks carrying acid gas. CorrosionGard-160S covers structures, vessels and tanks to 160 °C (320 °F); acid gas ducts and stacks move to FlueGard or StackGard grades.

How Do You Protect Process Vessels in a Chemical Plant from Corrosion?

Start from the chemical, concentration, temperature and exposure type in each zone of the vessel. CorrosionGard-160S lists storage tanks and pressure vessels handling corrosive gases and chemicals, is immersion-rated and is rated to 160 °C. Its bulletin shows weight gain below 0.5 % after one week in 10 % hydrochloric, 54 % phosphoric and 10 % sulfuric acid.

What Coating Resists Acid Fumes in a Chemical Plant?

A coating with documented resistance to the specific acid at the steel temperature. CorrosionGard-160S publishes immersion data in hydrochloric, phosphoric and sulfuric acid and 0 mm corrosion after more than 24 months of acid and salt spray weathering. Fume from other chemicals, such as organic acids or oxidizers, needs a review by Polylloy's technical team.

Does a Chemical Plant Coating Need Heat to Cure?

Not for structures and vessels coated with CorrosionGard-160S, which cures at room temperature and needs no process heat. The flue gas grades used on ducts and stacks, such as FlueGard-225SQC and StackGard-255SQW, are heat-cured: final heat cured activation is completed during start-up using process heat, so the start-up plan forms part of the coating plan.

Which Coating Protects Acid Gas Ducts and Stacks at a Chemical Plant?

Ducts and scrubbers carrying acid gas up to 225 °C can suit FlueGard-225SQC, which resists SO3, SO2, HCl, HF and NOx and is immersion-rated. Steel stacks up to 255 °C can suit StackGard-255SQW, and both grades are heat-cured at start-up. Neither bulletin lists chemical plants, so the gas chemistry is checked against each bulletin and confirmed per project.

Who Applies Polylloy Coatings at a Chemical Plant?

Certified Polylloy application partners carry out surface preparation and application. Polylloy formulates and supplies the coating, recommends the grade for each zone, writes the specification, trains the partner and supervises, including blasting to SSPC-SP10 near-white and inspection hold points. The network covers 15 partners across 22 countries.