Seal material chemical compatibility chart
The wrong seal fails without warning. In a heated cleaning tank that can mean hot caustic on the factory floor overnight. Every wetted part needs to suit the chemical, its concentration and the temperature: pump seals, valve seats, hoses, gaskets and tank fittings.
Use this chart to check the common seal and plastic materials against the chemistry used in industrial cleaning.
Seal and plastic materials against cleaning chemistry
Typical ratings at the concentration and temperature shown. Additives, mixtures and higher temperatures can change a rating, so test where the chart says C.
| Chemistry | EPDM | FKM (Viton) | NBR (nitrile) | PTFE | FFKM | Silicone | PP | PVDF |
|---|---|---|---|---|---|---|---|---|
| Strong caustic (sodium hydroxide)over 10%, 60 to 80 °C | A | D | C | A | A | D | A | C |
| Alkaline cleaner at working strength1 to 5% product, 60 to 80 °C | A | C | B | A | A | C | A | B |
| Mild alkaline detergentpH 9 to 11, up to 60 °C | A | B | B | A | A | B | A | A |
| Phosphoric acid cleanerdilute, up to 60 °C | A | A | C | A | A | C | A | A |
| Citric acid passivation4 to 10%, up to 60 °C | A | A | B | A | A | B | A | A |
| Nitric acid passivation20 to 50%, room temperature | C | A | D | A | A | D | C | A |
| Mineral oil and hydrocarbon solventroom temperature | D | A | A | A | A | D | C | A |
| Isopropyl alcoholroom temperature | A | A | B | A | A | B | A | A |
| Hot water80 to 90 °C | A | B | C | A | A | A | A | A |
What each material is good for, and where it fails
| Material | Good for | Watch for |
|---|---|---|
| EPDM | Hot water, steam, caustic and most acids and alkaline cleaners. About −40 to 150 °C. | Swells in neat oil, grease and hydrocarbon solvents. A water-based bath carrying some oily soil is usually fine; a floating oil layer or neat oil sitting on the seal is not. |
| FKM (Viton) | Oils, fuels, solvents and most acids. About −20 to 200 °C. | Attacked by hot strong caustic and amines. A common failure in alkaline cleaning lines. |
| NBR (nitrile) | Oils, greases and water-based cleaners at moderate heat. About −30 to 100 °C. | Hardens and cracks in hot water and steam over time. Poor with strong acids and oxidisers. |
| PTFE | Almost every cleaning chemical. Up to about 260 °C. | Not elastic: it creeps under load, so it is used as a lined or spring-energised seal, gasket or tape. |
| FFKM | Almost every chemical, including hot caustic and solvents. Up to about 300 °C. | High cost. Kept for pumps and valves where nothing else lasts. |
| Silicone | Hot water, mild detergents and static seals such as lid gaskets. Holds its shape under heat and pressure (low compression set). About −60 to 200 °C. | Weak against strong caustic, acids, oils and solvents, and tears easily if it rubs or flexes. Food and pharmaceutical grades (FDA, USP Class VI) resist chemicals no better: the grade is about purity, not chemical resistance. |
| PP (polypropylene) | Caustic, acids and alkaline cleaners. Up to about 90 °C. | Softens above that. Attacked by strong oxidising acids such as concentrated nitric. |
| PVDF | Acids, oxidisers and most solvents. Up to about 140 °C. | Can crack in hot strong caustic. Check before using it in an alkaline bath. |
The job the seal does matters as much as the chemistry
A static seal is squeezed once and stays put: a lid gasket or flange. What counts is compression set: how well it springs back after months under heat and pressure. A moving seal rubs: a pump shaft or valve stem. What counts there is wear and tear resistance. A material can be right for one and wrong for the other in the same chemistry.
| Material | Static seals (gaskets, lids, flanges) | Moving seals (pump shafts, valve stems) |
|---|---|---|
| EPDM | Good: low compression set | Good, as O-rings in pump mechanical seals |
| FKM (Viton) | Good: low compression set | Good |
| NBR (nitrile) | Fair | Very good: tough and wear resistant |
| PTFE | Poor: creeps under load (cold flow) | Very good when spring-energised: low friction |
| FFKM | Good | Fair to good |
| Silicone | Very good: very low compression set | Poor: tears and wears if it rubs or flexes |
| PP and PVDF | Rigid plastics, not seals | Used for pump bodies, pipe, fittings and tank linings |
How to check a machine
Pump seals, valve seats, hoses, gaskets, sight glasses and tank fittings, not just the pump.
The product, its concentration and the temperature you run at. A name alone is not enough.
Ask the supplier to state each material and confirm it against your chemistry. Why some machines cost less.
If you may switch chemistry later, choose materials that cover both, or plan to change the seals with it.
The chemical maker's technical advice and the seal maker's data confirm compatibility together. A safety data sheet alone is not a seal guide.
Swelling, hardening, cracking or a sticky surface means the seal is wrong for the job.
General advice only: check and test the materials in your own application before acting on anything on this page.
Where the ratings come from
The polymer-family ratings follow the published chemical resistance guides below. Each maker rates its own compounds; the exact compound and service conditions matter as much as the polymer family.
- Parker Hannifin, Parker O-Ring Handbook (ORD 5700): compatibility tables and compression set.
- Qnity (formerly DuPont), Elastomers Chemical Resistance Guide: FFKM (Kalrez) against other elastomer families.
- Chemours, Viton Chemical Resistance Guide: FKM by grade.
- ISO 1817, Rubber, vulcanized or thermoplastic: Determination of the effect of liquids. The standard test behind most published ratings.
The rows for alkaline cleaner at working strength, the temperature ranges shown and the static and moving seal table are Misonics engineering judgement from service experience, read against these guides. They are not laboratory test results.
Questions buyers ask
Which seal material is best for hot caustic?
EPDM, PTFE and FFKM. EPDM is the usual choice for hot alkaline cleaning at 60 to 80 °C. Silicone works as a static gasket in working-strength cleaners but softens in strong caustic. FKM (Viton) is a poor choice in hot strong caustic even though it is often fitted as a premium seal.
Is Viton compatible with sodium hydroxide?
Not in hot, strong caustic. FKM swells, hardens and cracks in it. Use EPDM, PTFE or FFKM for alkaline cleaning baths.
Which seals suit oily parts and solvent cleaning?
FKM, NBR, PTFE and FFKM for solvents and neat oil. EPDM swells in oil and hydrocarbon solvents. In a water-based cleaner carrying some oily soil EPDM is usually fine, but not where a floating oil layer or neat oil sits on the seal.
What is compression set?
How much a seal stays squashed after it has been compressed for a long time, often hot. Low compression set means it springs back and keeps sealing. Silicone and EPDM are good; PTFE creeps and needs a spring or a lined design to keep sealing.
Does temperature change seal compatibility?
Yes. A material rated good at room temperature can fail at 70 °C in the same chemical. Always check the rating at your concentration and your operating temperature, not just the chemical name.
What should I ask a supplier about seals?
Ask for the seal, hose, gasket and pump materials in writing, checked against your chemical, its concentration and the temperature you run at. It covers every wetted part, not just the pump.
Related pages
Why some cost less
The questions to ask before you buy on price.
Prove it before you buy
The factory test report, trials and commissioning.
Buyer's guide
How to choose an industrial ultrasonic cleaner.
Specification checklist
What to write down before you ask for quotes.
Chemical safety
Safety data and handling for cleaning chemistry.
Clean is a number
How cleanliness is measured.
Check your machine against your chemistry
Send the chemical, its concentration and the temperature you run at. Technical sales will tell you which seal, hose and pump materials suit it.