O-Rings for Chemical Processing
Chemical-resistant sealing for pumps, valves, reactors and pipework handling aggressive acids, solvents, oxidising chemicals and cryogenic fluids. Technical support and compatibility review.
Overview
Chemical processing plants handle aggressive media that rapidly degrade standard elastomeric seals — concentrated mineral acids, chlorinated solvents, strong oxidising agents, aromatic hydrocarbons, caustic alkalis, and reactive monomers at elevated temperatures and pressures. Seal failure in a chemical plant is not merely an operational inconvenience; it represents a potential safety hazard, environmental release, regulatory violation, and exposure liability. The consequences of selecting an incompatible seal material can include unplanned shutdowns costing hundreds of thousands of dollars in lost production, personnel exposure to hazardous or corrosive chemicals, and violations of environmental discharge permits. Material selection for chemical service is therefore one of the most critical engineering decisions in both new plant design and ongoing maintenance programmes.
Chemical compatibility cannot be assessed from generic material ratings or broad-brush chemical resistance charts alone. A fluorocarbon (FKM) seal may resist dilute sulfuric acid at 20% concentration and 40°C, yet fail catastrophically in 98% concentrated acid at 80°C through rapid dehydrofluorination. Similarly, EPDM performs well in dilute acids and alkalis but swells and degrades in even mild organic solvents such as ethanol or acetone. Concentration, temperature, pressure, and the presence of mixtures, contaminants, or trace catalysts all interact to determine actual compatibility in service. Engineers must specify seals based on compatibility data that matches their exact operating conditions. When published data is insufficient or unavailable, immersion testing under actual process conditions provides the most reliable validation and should be considered for critical applications.
Common failure modes in chemical service include chemical swelling, where volume increase of 25% or more causes extrusion from the seal groove under pressure; chemical hardening and cracking due to plasticiser extraction or cross-linking degradation that renders the seal brittle; explosive decompression in high-pressure gas systems where rapid pressure drop causes gas bubbles to expand within the elastomer matrix; and thermal degradation when continuous operating temperature exceeds the material's rated limit. Swelling increases seal friction and can cause the O-ring to extrude into clearance gaps under system pressure. Hardening leads to brittle fracture during assembly, thermal cycling, or vibration. Understanding these mechanisms enables predictive maintenance — seals can be replaced before they reach the failure threshold rather than after a leak occurs and chemical release has already happened.
Material selection for chemical processing follows a hierarchy based on chemical severity, temperature, and mechanical requirements. For general chemical service involving acids, petroleum derivatives, aromatic solvents, and aliphatic hydrocarbons at moderate temperatures, FKM offers the best balance of chemical resistance, mechanical properties, and cost. PTFE provides virtually universal chemical resistance and is the default choice for static seals, flange gaskets, lined components, and applications where elastomeric flexibility is not required. When FKM is inadequate — for concentrated oxidising acids, ketones, amines, esters, or temperatures above 200°C — FFKM provides the ultimate chemical and thermal resistance at significantly higher cost. For aqueous chemical service such as dilute acids, alkalis, bleach solutions, and steam, EPDM remains an economical and reliable option. Low-temperature FKM variants extend service into cryogenic chemical applications where standard FKM would harden and leak.
Specialised chemical process conditions require additional engineering considerations beyond simple chemical compatibility. In high-pressure gas systems handling hydrogen, carbon dioxide, methane, or ethylene, explosive decompression-resistant compounds prevent seal rupture when pressure is rapidly released during venting or depressurisation cycles. In cryogenic chemical service such as liquid nitrogen, LNG, or ethylene refrigeration, special low-temperature FKM or PTFE is required to maintain seal flexibility below -30°C where standard elastomers become glassy and brittle. For strong oxidising agents including concentrated nitric acid, hydrogen peroxide, chlorine dioxide, or chromic acid, PTFE or FFKM is typically required as standard FKM may degrade through oxidation of the polymer backbone. Our engineering team can evaluate your specific chemical, concentration, temperature, pressure, decompression profile, and regulatory requirements to specify the optimal material and seal design.
We support chemical processing customers with more than just material supply. Our technical service includes detailed chemical compatibility review based on your process data sheets and operating envelopes, finite element analysis for seal groove design optimisation in high-pressure or high-temperature applications, and forensic failure analysis of returned seals to determine root cause and prevent recurrence. All chemical-grade O-rings are supplied with material certificates of conformance, batch traceability documentation, and physical property test reports. For critical applications or unproven chemical combinations, we can arrange third-party independent immersion testing to verify chemical compatibility under your specific conditions. Whether you are designing a new reactor, upgrading a valve train, replacing seals in a solvent recovery column, or managing a plant-wide predictive maintenance programme, our applications engineers can provide material recommendations backed by data, experience, and testing.
Recommended Materials
FKM (Viton)
General chemical service including acids, petroleum-based chemicals, aromatic solvents, aliphatic hydrocarbons, and H2S service in valves, pumps, and reactors.
Temp: -20°C to +200°C
Note: First choice for most chemical environments. Avoid ketones, strong bases, and low-molecular-weight esters.
PTFE Virgin
Universal chemical resistance for static seals, flange gaskets, face seals, and lined components where elastomeric properties are not required.
Temp: -200°C to +260°C
Note: Resists virtually all chemicals. Limited to static applications due to low elasticity and cold-flow tendency.
FFKM (Kalrez)
Ketones, concentrated oxidising acids, amines, esters, steam, and temperatures above 200°C — applications where FKM degrades.
Temp: -15°C to +325°C
Note: Premium material for extreme chemical and thermal environments. Cost is justified by extended service life and reduced downtime.
EPDM
Dilute acids, alkalis, bleach solutions, steam, water-based chemicals, and phosphate ester hydraulic fluids in aqueous chemical service.
Temp: -50°C to +150°C
Note: Economical choice for aqueous chemical service. Not suitable for organic solvents, oils, or aromatic hydrocarbons.
Low-Temperature FKM
Cryogenic chemical service including LNG, liquid nitrogen, ethylene refrigeration, and cold solvent handling where standard FKM would harden.
Temp: -40°C to +200°C
Note: Maintains sealing flexibility at sub-zero temperatures where standard FKM becomes glassy and brittle.
Typical Applications
- Reactor vessel seals
- Pump seals
- Agitator seals
- Heat exchanger seals
- Valve stem seals
- Flange gaskets
- Sampling port seals
- Pressure vessel seals
Relevant Standards
Frequently Asked Questions — Chemical Processing
What O-ring resists hydrofluoric acid (HF)?
FKM fluorocarbon elastomers offer excellent resistance to hydrofluoric acid across most industrial concentrations and temperatures encountered in chemical processing. HF is a particularly aggressive acid because the fluoride ion penetrates and attacks many polymer backbones, but the carbon-fluorine bonds in FKM provide exceptional stability. For static applications requiring maximum resistance or for very high concentrations above 70%, PTFE is an alternative that provides virtually universal chemical inertness. FFKM perfluoroelastomer is specified for high-concentration HF at elevated temperatures above 100°C or where both HF and organic solvents are present. NBR nitrile and EPDM are not suitable for HF service under any conditions — NBR will harden and crack rapidly, while EPDM will swell and degrade. When specifying seals for HF, it is critical to consider not only the acid concentration but also the presence of contaminants, the temperature profile, and whether the application is static or dynamic. We can provide immersion test data for FKM in HF at various concentrations and temperatures.
Which O-ring material for chlorinated solvent service?
FKM is the material of choice for most chlorinated solvent applications including trichloroethylene, methylene chloride, perchloroethylene, and 1,1,1-trichloroethane. The fluorinated polymer structure of FKM resists the swelling and extraction effects that chlorinated solvents inflict on hydrocarbon-based elastomers. NBR nitrile rubber is severely attacked by chlorinated solvents and will swell excessively, lose mechanical properties, and fail within days or weeks. PTFE also provides excellent resistance to chlorinated solvents and is frequently used for static seals, flange gaskets, and valve seats in solvent recovery and degreasing equipment. For applications involving mixtures of chlorinated solvents with amines or strong bases, FFKM may be required as FKM can degrade in strongly basic environments. When selecting seals for chlorinated solvent service, always verify the specific solvent identity, concentration, temperature, and whether the solvent is used neat or in aqueous solution, as these factors significantly affect compatibility.
Can any O-ring resist concentrated sulfuric acid?
PTFE provides the best resistance to concentrated and fuming sulfuric acid across the full concentration range from 70% to oleum. The carbon-fluorine bond energy in PTFE makes it virtually inert to sulfuric acid at all practical temperatures. FKM resists moderate concentrations of sulfuric acid up to approximately 70% at moderate temperatures but degrades in concentrated or fuming grades through dehydrofluorination reactions. FFKM perfluoroelastomer resists a wider range of concentrations and temperatures than FKM and is often specified for dynamic seals in sulfuric acid service where PTFE cannot be used. EPDM is suitable only for very dilute sulfuric acid below 10% concentration and will degrade rapidly in concentrated acid. For sulfuric acid applications, temperature is as critical as concentration — a material that resists 50% acid at 40°C may fail in the same concentration at 80°C. We recommend providing your exact concentration, temperature, and application type for a definitive compatibility recommendation.
What about ATEX requirements in chemical plants?
ATEX directives apply to equipment used in potentially explosive atmospheres containing flammable gases, vapours, mists, or dusts. While ATEX does not directly specify O-ring materials, it governs the overall equipment design and requires that all components including seals are suitable for the explosive atmosphere. In ATEX zones, O-ring material selection should focus on preventing ignition sources. Highly insulating elastomers can accumulate static charge in certain high-velocity gas or powder applications, potentially creating an electrostatic discharge hazard. In such cases, static-dissipative or conductive seal materials may be required. Additionally, O-ring materials must be chemically compatible with the explosive atmosphere media to prevent degradation that could create gaps or leaks. Temperature ratings must also be verified to ensure that seal friction or process temperature does not exceed the auto-ignition temperature of the explosive atmosphere. We can advise on material selection for ATEX-rated equipment and supply seals with material certificates suitable for your equipment certification dossier.
How does explosive decompression affect O-rings in gas service?
Explosive decompression (ED), also known as rapid gas decompression, is a failure mode that occurs in high-pressure gas systems when pressure is reduced faster than the gas dissolved in the elastomer can diffuse out. Under high pressure, gases such as carbon dioxide, methane, hydrogen, and ethylene dissolve into the elastomer matrix and permeate throughout the seal. When system pressure is rapidly released — for example during venting, maintenance, or emergency shutdown — the dissolved gas comes out of solution and forms blisters within the elastomer. If the pressure drop is sufficiently rapid, these blisters expand faster than the elastomer can accommodate, causing internal cracking, surface blistering, and seal rupture. The damage is often visible as internal fissures or surface pitting and can cause immediate leakage or progressive failure. ED-resistant compounds are formulated with lower gas permeability, better adhesion between polymer and filler, and optimised cross-link density to resist blister formation. For critical gas service, we recommend specifying ED-resistant FKM or FFKM grades and designing systems with controlled depressurisation rates where possible.
What causes O-ring swelling in chemical applications?
O-ring swelling in chemical service is caused by absorption of the process fluid into the elastomer matrix, which increases seal volume and alters mechanical properties. Swelling occurs when the chemical medium has similar solubility parameters to the polymer, allowing molecules to penetrate and plasticise the elastomer. For example, hydrocarbon oils and solvents swell NBR and EPDM because the non-polar solvents interact with the hydrocarbon polymer chains. Acetone and ketones swell standard FKM because these polar solvents interact with the polar vinylidene fluoride segments in the polymer. Swelling increases seal volume by 10% to over 100% depending on the material and chemical, which can cause extrusion into clearance gaps, increased friction, and loss of sealing force as the material softens. In severe cases, swollen seals can jam valves, seize pumps, or block fluid passages. The degree of swelling depends on temperature, concentration, exposure time, and material formulation. Selecting a material with low affinity for the specific chemical is the primary prevention strategy. PTFE and FFKM exhibit minimal swelling in virtually all chemicals.
Can FKM O-rings be used with ketones and amines?
Standard FKM is generally not recommended for service with ketones, amines, low-molecular-weight esters, and strong bases. Ketones such as acetone, methyl ethyl ketone, and cyclohexanone cause significant swelling in standard dipolymer and terpolymer FKM grades because the polar carbonyl groups in the ketone interact strongly with the polar vinylidene fluoride units in the polymer backbone. Amines including ammonia, methylamine, and ethanolamine attack FKM through nucleophilic degradation of the polymer chain, causing embrittlement and cracking. Strong bases such as concentrated sodium hydroxide and potassium hydroxide also degrade FKM through dehydrofluorination reactions. For ketone and amine service, FFKM perfluoroelastomer is the recommended material because its fully fluorinated backbone lacks the vulnerable vinylidene fluoride segments. PTFE is also suitable for static seals in ketone and amine environments. Speciality FKM copolymers with improved base resistance exist for specific applications, but FFKM remains the safest choice for broad chemical compatibility.
What is the maximum temperature for PTFE O-rings in chemical service?
PTFE O-rings can withstand continuous operating temperatures up to 260°C and short-term exposure up to 300°C in chemical service, making them the highest-temperature sealing material available for general chemical applications. The upper temperature limit is governed not by chemical degradation — PTFE does not decompose until approximately 400°C — but by physical property changes and cold flow. As temperature increases above 150°C, PTFE begins to soften significantly and cold flow rates increase, meaning the seal may deform permanently under sustained compressive load. At temperatures above 260°C, the rate of creep becomes excessive for most sealing applications and the seal may extrude from the groove or lose contact pressure. In cryogenic chemical service, PTFE maintains flexibility down to -200°C, which is far below the capability of any elastomer. For high-temperature dynamic applications where PTFE cold flow is problematic, filled PTFE grades with glass fibre, carbon, or bronze additives improve creep resistance and wear properties. For temperatures above 260°C where elastomeric recovery is required, FFKM is the only viable alternative.
How do I select between FKM and FFKM for my chemical process?
Selecting between FKM and FFKM requires a systematic evaluation of chemical compatibility, temperature, mechanical requirements, and total cost of ownership. FKM should be your first choice for general chemical service involving acids, petroleum chemicals, aromatic solvents, and aliphatic hydrocarbons at temperatures up to 200°C. It offers excellent chemical resistance, good mechanical properties, and reasonable cost. FFKM becomes necessary when FKM is chemically incompatible — specifically with ketones, amines, strong bases, concentrated oxidising acids, and certain esters — or when continuous operating temperature exceeds 200°C. FFKM also outperforms FKM in steam service and provides longer service life in aggressive environments, which can justify its premium cost through reduced maintenance and downtime. The decision should be based on a compatibility review of your specific chemicals at actual concentrations and temperatures. For non-critical applications or large seal quantities where FFKM cost is prohibitive, PTFE may be an alternative for static seals. Our applications engineers can perform a detailed compatibility assessment and life-cycle cost analysis to help you make the optimal selection.
Do you provide chemical immersion testing services?
Yes, we provide chemical immersion testing services for critical applications where published compatibility data is insufficient or where multiple chemicals are present in mixtures that are not covered by standard reference charts. Our testing programme includes volume change measurement, hardness change, tensile strength and elongation retention, compression set, and visual inspection after immersion in your process fluid at specified temperature and duration. Tests can be performed according to ASTM D471, ISO 1817, or custom protocols designed to match your operating conditions. For pharmaceutical and food applications, we can also perform extractables testing on immersed samples. Typical test durations range from 7 days for initial screening to 30, 60, or 90 days for long-term compatibility validation. We provide comprehensive test reports with data tables, photographs, and material recommendations based on the results. For high-risk applications, we recommend a two-stage approach: initial screening with candidate materials followed by long-term validation with the selected optimal compound. Contact our laboratory services team with your process fluid composition, operating temperature, and test requirements for a customised testing proposal and quotation.