Chemical Resistance Testing
How coatings and linings are tested against acids, alkalis, solvents and process fluids — spot tests, immersion, one-sided cells and autoclaves — and how to read a chemical resistance chart.
Key takeaways
- Chemical resistance depends on the specific chemical, its concentration, temperature and exposure time — “acid resistant” means little without those details.
- Test methods range from short spot tests for spills to long-term immersion and one-sided cell tests for tank and vessel linings.
- Evaluation looks for blistering, softening, swelling, discoloration, weight change and loss of adhesion, not just visible attack.
- Manufacturer resistance charts are a starting point. For critical or unusual exposures, test the actual chemical under service conditions.
Floors in battery rooms, linings in acid tanks, containment around fuel storage and coatings in food plants all face chemicals that can soften, swell, blister or dissolve the wrong coating. Chemical resistance testing tells specifiers which systems can survive a given exposure — and for how long — before they are put into service.
What chemical resistance means
A coating resists a chemical when it keeps its integrity, adhesion and protective function during and after exposure. Failure can take several forms:
- Dissolution or softening — the chemical attacks or plasticizes the polymer.
- Swelling and permeation — the chemical is absorbed and passes through the film to the substrate.
- Blistering — liquid collects under or within the film; see blistering.
- Chemical reaction — oxidizing acids, for example, can degrade a resin backbone.
- Discoloration or staining — sometimes only cosmetic, sometimes an early warning.
Resistance depends strongly on chemical type, concentration, temperature and duration. A coating that tolerates a dilute acid at room temperature may fail quickly in the concentrated acid or at elevated temperature. Mixtures can be more aggressive than either component alone.
Test methods
Spot and covered spot tests
For spills and splashes, a small amount of chemical is placed on a cured coating and left open to evaporate or covered with a watch glass to prevent evaporation for a set time. After removal, the area is inspected for changes. ASTM D1308 covers the effect of household chemicals on clear and pigmented organic finishes, and ISO 2812-4 covers spotting methods. These tests are well suited to floors, laboratory surfaces and food-plant walls.
Immersion tests
Coated panels or rods are partly or fully immersed in the test liquid at a set temperature for days to months. ISO 2812-1 covers immersion in liquids other than water, and ISO 2812-2 and ASTM D870 cover water immersion. Coated edges and backs must be protected so attack starts only on the test face.
One-sided (Atlas cell) tests
Tank and vessel linings are exposed to liquid on one side while the steel behind them is cooler — a temperature gradient that drives permeation and blistering. NACE TM0174 describes laboratory methods for evaluating coatings and linings in immersion service, including a one-sided test cell, and ASTM C868 covers chemical resistance of protective linings using a similar cell. These tests better represent real storage tank linings than full immersion of a panel.
Autoclave tests
For oil and gas service at high pressure and temperature, autoclave tests expose coatings to mixtures of liquids and gases such as hydrocarbons, water, carbon dioxide and hydrogen sulfide, followed by rapid decompression. NACE TM0185 covers autoclave testing of internal coatings for tubular goods.
Floor and surfacing tests
ASTM C267 covers chemical resistance of mortars, grouts, monolithic surfacings and polymer concretes by immersing cast specimens and measuring weight change, appearance and strength retention.
| Method | Exposure simulated | Typical duration | Best for |
|---|---|---|---|
| Spot test (ASTM D1308, ISO 2812-4) | Spills and splashes | Minutes to days | Floors, walls, benches |
| Immersion (ISO 2812-1) | Continuous contact | Days to months | Screening linings and coatings |
| One-sided cell (NACE TM0174, ASTM C868) | Immersion with temperature gradient | Weeks to months | Tank and vessel linings |
| Autoclave (NACE TM0185) | High pressure, gas and liquid | Hours to days per cycle | Oil and gas internals |
| Surfacing immersion (ASTM C267) | Continuous contact | Weeks to months | Mortars, polymer concrete, toppings |
Evaluating results
Inspection after exposure typically includes:
- Blistering, rated for size and frequency with ASTM D714 photographic standards.
- Hardness change, for example by pencil hardness or durometer, immediately after removal and after a recovery period.
- Weight or thickness change, indicating absorption or loss of material.
- Adhesion by knife or pull-off test, compared with unexposed controls.
- Appearance — gloss loss, color change, cracking or staining.
Always test an unexposed control panel from the same batch alongside the exposed panels. Without a baseline, changes in hardness or adhesion are difficult to attribute to the chemical.
Reading chemical resistance charts
Manufacturers publish chemical resistance guides for their products, usually with categories such as recommended for immersion, splash and spill or secondary containment (often with a time limit such as 72 hours), conditional and not recommended. These ratings are based on the manufacturer’s testing at stated concentrations and temperatures.
Read the notes carefully: ratings usually assume a fully cured coating at the specified thickness, often at around room temperature. Discoloration may be listed as acceptable even when the film is otherwise unaffected. If your chemical, concentration or temperature is not listed, ask the manufacturer or test. The product data sheet and resistance guide should be read together.
Full cure is essential. Most resistance data assume the coating has reached full cure, which can take days to weeks depending on temperature. Exposing a partially cured lining to chemicals is a common cause of early failure.
Matching tests to service
Choose test methods that mirror how the coating will actually be exposed. Secondary containment linings need to hold a spill until it is cleaned up, so a covered spot or short immersion test at the expected temperature is appropriate. Process vessels and tanks need long-term one-sided testing. In aggressive acid service, chemistries such as novolac epoxies and vinyl esters are commonly evaluated, while chemical plant coatings often combine several systems for different zones.
Frequently asked questions
Why does temperature matter so much?
Higher temperature speeds up chemical attack and permeation and can soften the coating, especially near its glass transition temperature. A rating at room temperature may not apply at elevated temperature.
What does “splash and spill” mean on a chart?
It means the coating tolerates intermittent contact if the chemical is cleaned up within a stated time, but it is not suitable for continuous immersion.
Can I trust a generic chemical resistance table for a resin type?
Only as a rough guide. Formulations within a chemistry vary widely, so use the specific product’s data and test critical exposures.
Educational reference. Coating performance varies by formulation. Always follow the manufacturer’s product data sheet, safety data sheet and your project specification.
