Sodium Sulfide and Sulfite O-Ring Compatibility: Which Compounds Hold Up
Sodium sulfide and sulfite O-Ring guide for pulp and paper, chemical process, and reducing-agent service: chart ratings, why nitrile is the preferred start, and which elastomer lacks data.
Sodium sulfide and sodium sulfite are inorganic reducing salts used in pulp and paper, chemical manufacturing, water treatment, and related process service. Seals on transfer valves, dosing pumps, digester-related piping, bleach-plant auxiliaries, and storage fittings see aqueous sulfide or sulfite solutions that are polar and often alkaline. Pick poorly and you still risk swell, softening, or early weep when concentration, heat, or co-fluids stack against the elastomer.
This guide maps the handbook Chemical Compatibility Chart row for sodium sulfide and sulfite to practical compound choices. The row is unusually forgiving: nearly every common family rates excellent (1), so selection often turns on cost, temperature, and plant standards rather than a narrow chemical shortlist.
Where it shows up
- Pulp and paper: kraft and sulfite-related chemistry, digester auxiliaries, and bleach-plant or liquor handling loops that move sulfide or sulfite salts
- Chemical manufacturing: feedstock and intermediate reducing-agent duty for dyes, organics, and specialty salts
- Water treatment and dechlorination: sulfite-based oxygen scavengers and chlorine residual control on dosing skids
- Leather, mining, and specialty reagents: sulfide-ion sources and related aqueous reducing baths
- Drum, tote, and bulk transfer: fill heads and pump skids moving concentrated or dilute aqueous solutions
Service is usually aqueous, near ambient to moderately warm. Concentration, pH, and any free H2S risk still matter. Chart ratings assume a generic commercial compound near room temperature.
How sodium sulfide and sulfite stress an O-Ring
These solutions are polar, reducing, often alkaline salt media. Unlike aromatic solvents that punish oil-service stocks, this chart row shows broad elastomer compatibility. That does not mean every grade is equal: heat, continuous immersion, solids, and co-fluids still drive swell and aging. Alkaline sulfide streams can also evolve hydrogen sulfide if acidified or poorly vented, so seal choice does not replace safe handling. See Chemical Compatibility and Failure Analysis.
Handbook chart ratings for sodium sulfide and sulfite
Same rating badges and layout as the interactive chart. Search Sodium Sulfide and Sulfite on the Chemical Compatibility Chart to pin the live row.
| Fluid | Best | N Nitrile | H HNBR | E EPDM | C Neoprene | S Silicone | V Viton® | P Urethane | F FVMQ | A Aflas® | B Butyl | K FFKM | T PTFE |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sodium Sulfide and Sulfite | N | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | X | 1 | 1 | 1 |
Best family on the chart row: Nitrile (N). HNBR, EPDM, neoprene, silicone, FKM, polyurethane, fluorosilicone, butyl, FFKM, and PTFE also rate excellent (1). Aflas® lacks data (X) on the handbook matrix. Compatibility here is broad; nitrile is the chart’s preferred letter when cost and availability matter.
Recommended O-Ring materials
First choice: Nitrile (Buna-N)
Nitrile (NBR) is rated excellent (1) and is the chart’s preferred letter for sodium sulfide and sulfite. Use it for ambient to moderately warm aqueous service on valves, flanges, and transfer seals when cost and stock availability matter. HNBR matches that chemical rating with more heat and wear margin for pumps and frequent cycling. Use 70 Shore A for most static covers; step hardness or add a back-up ring when pressure and clearance gap climb.
Also usually serviceable
Materials to treat as unknown
Physical properties to match (after chemistry)
A chart 1 means the polymer family usually survives the fluid. Finish the spec with the gland and process needs:
- Hardness: 70 Shore A for most static covers and flanges; 90 Shore A or a back-up ring when pressure and gap climb (Shore A Hardness).
- Temperature: handbook chemical ratings are near room temperature. Warm liquor lines and heat-traced dosing age seals faster. Confirm continuous temperature against the Temperature Guide.
- Static vs dynamic: face and cover seals are mostly static; shafts and rods need abrasion and extrusion control beyond a chemical letter (groove design).
- Size: lock ID × CS (or the AS568 dash) on the Master O-Ring Size Chart before arguing compound.
Practical selection checklist
- Confirm sulfide vs sulfite, concentration, pH, and any co-solvents or free H2S risk on the SDS.
- Note temperature and whether the seal sees liquid, vapor, or both.
- Start with nitrile at 70 Shore A for general static duty unless heat, abrasion, or a plant standard already calls for HNBR, EPDM, FKM, or PTFE-encapsulated.
- Treat Aflas® as unproven on this chart row until you test.
- Pin Sodium Sulfide and Sulfite on the Chemical Compatibility Chart. For critical service, contact The O-Ring Store with fluid grade, temperature, hardness, and duty cycle.
Quick answers
Which O-Ring for sodium sulfide and sulfite?
Start with nitrile (Buna-N) at 70 Shore A for general static duty. HNBR, EPDM,
neoprene, silicone, FKM, polyurethane, fluorosilicone, butyl, FFKM, and PTFE also rate
excellent. Compatibility is broad; prefer nitrile when the chart letter and cost both matter.
Treat Aflas® as unproven here until you test.
Is sodium sulfide the same as sodium sulfite or sodium hydrosulfite on the chart?
Related reducing salts show up in the same plants. Always match the exact fluid name on
the chart and on the SDS.
Chart ratings are guidance for generic commercial compounds near room temperature. Concentration, temperature, and co-fluids change outcomes. Evaluate specific parts before use in critical applications.
