Secondary Containment Coating Systems for Industrial Contractors
Article 03 of 24
Chemical Exposure, Concentration, Temperature, and Contact Time
Chemical resistance is not a permanent property that can be described
with a simple yes or no. It depends on what contacts the lining, how
strong it is, how hot it is, and how long it remains.
Learning Objectives
After completing this article, you should be able to:
- Explain the four primary chemical-exposure variables
- Recognize how concentration and temperature change chemical attack
- Differentiate splash, spill, pooling, intermittent exposure, and immersion
- Recognize the risks created by mixtures and changing concentrations
- Interpret chemical-resistance information more carefully
- Document exposure conditions for manufacturer review
Four Variables—One Exposure
The four primary variables are interconnected:
- Chemical identity: What material will contact the system?
- Concentration: How strong is the material?
- Temperature: How hot or cold will it be?
- Contact time: How long will it remain on the system?
Changing any one of these variables may change the suitability of the
lining. A product that performs acceptably under one set of conditions
may fail under another.
Chemical Identity: Use the Complete Name
Product descriptions such as acid, solvent, cleaner, oil, fertilizer,
wastewater, or process chemical are not specific enough for lining
selection. The manufacturer needs the complete chemical or product
identification.
Whenever possible, provide:
- The recognized chemical name
- Trade or product name
- Manufacturer or supplier
- Chemical Abstracts Service numbers when available
- Safety Data Sheet
- Known ingredients and percentages
- Process contaminants or byproducts
- Whether the material is a liquid, slurry, paste, vapor, or solid-bearing solution
Two products sold for the same purpose may contain different solvents,
additives, salts, surfactants, or reactive ingredients. Never assume
that products with similar trade descriptions create identical exposure.
Concentration: More Than a Percentage on Paper
Chemical concentration can affect reaction rate, permeation, swelling,
softening, discoloration, loss of adhesion, and damage to the substrate.
The relationship is not always simple or linear.
Determine the following:
- Normal operating concentration
- Maximum intended concentration
- Maximum credible upset concentration
- Concentration following dilution or washdown
- Concentration after evaporation
- Whether solids can settle or concentrate in low areas
- Whether the concentration changes during storage or processing
Do not assume that a more dilute solution is always less severe.
Changes in water content can affect ion movement, permeation, osmotic
pressure, and the behavior of both the polymer lining and concrete.
Use resistance data for the actual concentration range.
Temperature: A Major Chemical-Resistance Variable
Higher temperature commonly increases the rate at which chemicals react
with, soften, penetrate, or pass through a protective lining. It can also
increase vapor pressure and place additional stress on the bond between
the lining and substrate.
Record each relevant temperature:
- Normal operating temperature
- Maximum continuous temperature
- Maximum spill or upset temperature
- Lowest winter or shutdown temperature
- Cleaning and washdown temperature
- Substrate temperature during service
- Rate and frequency of temperature change
A system rated for a chemical at 75°F should not be assumed suitable
for the same chemical at 140°F. The manufacturer must confirm the
approved combination of chemical, concentration, temperature, and
exposure duration.
Contact Time: Seconds, Hours, Days, or Continuous Service
Resistance during brief splash exposure does not establish suitability
for prolonged pooling or immersion. Many chemical-resistance ratings
depend on the expected duration of contact.
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Exposure Type
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Typical Condition
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Selection Concern
|
|
Splash
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Droplets or small releases removed promptly
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Repeated exposure and cleaning may still damage the system
|
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Spill
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Accidental release followed by response and recovery
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Actual response time must be defined
|
|
Pooling
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Liquid remains in depressions, corners, or around equipment
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Local contact may continue after the visible spill is removed
|
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Intermittent
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Repeated wet and dry exposure
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Cycling may create swelling, shrinkage, or repeated stress
|
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Immersion
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Continuous or sustained liquid contact
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Requires specific approval for immersion service
|
Cleanup Time Must Be Realistic
An owner may expect a spill to be removed immediately. Actual conditions
may tell a different story. A release can occur during an unattended
shift, severe-weather event, power interruption, equipment failure, or
emergency that prevents immediate entry.
The project should identify the longest credible period before the
material can be safely recovered and the area decontaminated. The
proposed system should be evaluated for that duration—not an
unsupported best-case response time.
Low spots, sumps, cracks, joints, and spaces beneath equipment may
remain wet after general cleanup. These locations can receive much
longer contact than the open floor.
Mixtures Can Behave Differently
Separate resistance ratings for Chemical A and Chemical B do not prove
that the lining will resist a mixture of A and B. Mixing can produce
heat, precipitation, gas, a new chemical species, or a different
penetration mechanism.
Fire-suppression water, rainwater, wash water, cleaners, oils, process
residue, and neighboring stored materials can all change the exposure.
Identify credible mixtures and provide them to the system manufacturer.
When mixture data are unavailable, the owner or design professional may
require laboratory testing, exposure coupons, a test installation, a
more conservative system, or additional protective measures.
Physical Form Also Matters
Exposure is not limited to clear liquids. A containment system may
encounter:
- Slurries containing abrasive solids
- Viscous liquids that are difficult to recover
- Solvents capable of rapid permeation
- Hot liquids that cool and contract after release
- Powders that dissolve during rain or washdown
- Vapors that condense on walls or overhead surfaces
- Materials that crystallize or leave aggressive residues
The physical form affects recovery, cleaning, abrasion, penetration,
drainage, and the length of time residues remain in contact with the system.
Chemical Attack Can Reach the Substrate
The lining is intended to isolate the substrate, but pinholes, holidays,
cracks, damaged areas, joints, and penetrations can permit chemical entry.
The potential effect on the substrate must therefore be considered.
Acids may dissolve or weaken cement paste. Some salts and solutions may
contribute to expansion, softening, corrosion, or loss of bond. Solvents
and oils may penetrate porous concrete and complicate future repairs.
Chemical attack at a small discontinuity can spread beneath an otherwise
intact-looking lining.
The specification should therefore address continuity, detail work,
inspection, holiday detection where appropriate, and repair—not only
the resistance of the coating resin.
Understanding Chemical-Resistance Ratings
Manufacturers use different rating systems. A chart may use terms such
as recommended, suitable, conditional, limited, splash only, not
recommended, or consult technical service. Those terms must be read
according to that manufacturer’s definitions.
Confirm whether the rating addresses:
- A resin sample or a complete installed system
- Splash, spill, fumes, intermittent contact, or immersion
- A specific concentration and temperature
- A specific exposure duration
- Change in weight, dimensions, hardness, appearance, or strength
- Discoloration that does not necessarily mean structural failure
- Laboratory conditions that may differ from field conditions
A chart entry is useful for screening possible materials. Final selection
should be based on the complete exposure and a written recommendation
for the complete system.
Information to Send the Manufacturer
- Complete chemical and product names
- Safety Data Sheets and available composition data
- Normal and maximum concentrations
- Normal and maximum temperatures
- Exposure type and maximum credible contact time
- Possible mixtures and exposure sequence
- Cleaning agents, methods, pressures, and temperatures
- Substrate type and existing condition
- Indoor, outdoor, ultraviolet, and weather exposure
- Traffic, abrasion, impact, vibration, and movement
- Required return-to-service schedule
- Applicable specification and inspection requirements
Request a written response identifying the complete recommended system,
thickness, preparation, detail requirements, cure before exposure,
limitations, and inspection requirements.
Practical Example
A project description states only that a concrete containment area will
hold an acid-storage tank. That description is incomplete.
Before a system is selected, the project team must determine:
- Which acid is stored
- Its normal and maximum concentration
- Its normal and maximum spill temperature
- The maximum time before recovery
- Whether water, cleaner, or another chemical may mix with it
- How the area will be cleaned and neutralized
- Whether the manufacturer approves the complete system for that exposure
Until those questions are answered, a responsible contractor cannot
confirm that a proposed lining is appropriate.
Technical References
Test methods and published ratings do not automatically approve a
product for a particular project. Verify the current document edition,
the manufacturer’s interpretation, and all project-specific requirements.
Key Takeaways
- Chemical resistance depends on identity, concentration, temperature, and contact time
- The four variables must be evaluated together
- Splash resistance does not establish immersion resistance
- Mixtures and changing concentrations require separate consideration
- The physical form of the material affects recovery and exposure
- Chemical-resistance charts are screening tools—not complete project approvals
- Obtain the manufacturer’s recommendation in writing
Professional responsibility:
Do not approve a containment system using incomplete exposure
information or a generic resin description. Chemical compatibility
must be evaluated for the complete system and the actual service
conditions.
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