Phosphoric Acid Resistant O-Rings

Compatibility ratings for 7 O-ring materials in Phosphoric Acid service

At a glance:A× 3B× 4C× 0D× 0— 3 of 7 materials recommended for Phosphoric Acid

Phosphoric Acid (Acids) compatibility with the seven most common O-ring elastomers, rated on the standard A/B/C/D scale: A = excellent, B = good, C = fair, D = not recommended. This data also appears in our interactive chemical compatibility chart and is available machine-readable at /api/chemicals.json.

Material	Rating	Guidance
NBR	B	good — suitable for most applications
FKM	A	excellent — recommended for continuous service
EPDM	B	good — suitable for most applications
VMQ	B	good — suitable for most applications
PTFE	A	excellent — recommended for continuous service
FFKM	A	excellent — recommended for continuous service
HNBR	B	good — suitable for most applications

Why These Ratings

FKM (A) — documented strengths include “Strong acids.”
PTFE (A) — documented strengths include “Strong oxidizing acids.”
FFKM (A) — documented strengths include “Concentrated oxidising acids.”

AcidsService: Concentration & Temperature Notes

Concentration changes everything in acid service. In our own data, sulfuric acid shifts NBR from C (dilute) to D (concentrated) and EPDM from B to C as concentration rises. Oxidizing acids (nitric, concentrated sulfuric) attack the polymer backbone chemically rather than merely swelling it, which is why PTFE and FFKM dominate this category. Temperature accelerates acid attack sharply — a rating earned at room temperature may not hold at +60°C.

Use With Caution

Avoid

No material is rated D for this chemical.

Engineering note: ratings are general guidelines based on typical exposure conditions. Fluid concentration, temperature, pressure and exposure time can shift compatibility by a full grade or more. For critical service, validate the actual compound with ASTM D471 immersion testing before production use. Selecting across multiple chemicals? See the chemical-resistant O-ring selection guide for a material-first comparison.

Related Chemicals (Acids)

Frequently Asked Questions

Is Phosphoric Acid compatible with FKM (Viton) O-rings?

FKM is rated A for Phosphoric Acid: excellent — recommended for continuous service. Ratings are general guidelines; concentration, temperature and exposure time all affect real-world compatibility, so validate critical applications with ASTM D471 immersion testing.

Is Phosphoric Acid compatible with NBR (nitrile) O-rings?

NBR is rated B for Phosphoric Acid: good — suitable for most applications. NBR is the lowest-cost elastomer, so when it earns an A or B rating it is usually the economical default; when it rates C or D, do not substitute it for a higher-rated material to save cost.

Can I use PTFE O-rings with Phosphoric Acid?

PTFE is rated A for Phosphoric Acid: excellent — recommended for continuous service. Remember that PTFE has no elastic memory — in demanding service it needs spring energization or an elastomer core (FEP/PFA encapsulation) to maintain sealing force.

What is the best O-ring material for Phosphoric Acid?

FKM, PTFE, FFKM are rated A (excellent) for Phosphoric Acid in our compatibility data and are the recommended starting point for material selection. Final selection should also account for operating temperature, pressure and whether the seal is static or dynamic.

Can I use EPDM O-rings with Phosphoric Acid?

EPDM is rated B for Phosphoric Acid: good — suitable for most applications. Always confirm the specific fluid concentration and temperature before specifying EPDM for this service.

Need O-Rings for Phosphoric Acid Service?

Send us your fluid, concentration and temperature — our engineers will confirm the right compound. MOQ 1 piece.

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