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Sodium Hydroxide (Caustic) Storage — Tank, Resin & System Selection

Storing Sodium Hydroxide (Caustic Soda)? Start Here

50% caustic soda is one of the easiest corrosive chemicals to store in a poly tank — with one catch most people forget: it crystallizes (turns slushy/solid) when it gets cold. Keep it warm and you'll have zero trouble. And here's a twist from the acid pages — caustic is one of the rare chemicals where EPDM gaskets are the right choice, not Viton.

Can you store it in a poly tank? Easily.

50% sodium hydroxide is compatible with HDPE and crosslinked XLPE chemical-service tanks (1.9 SG). Use EPDM gaskets, PVC fittings, and 316 stainless bolts. Yes — EPDM, not Viton. In strong caustic, EPDM actually outlasts Viton, which is the opposite of the acids. (Spec it wrong and you'll be chasing seal leaks.)

The catch: keep it warm

50% caustic begins to crystallize as it cools toward the mid-50s°F — it gets slushy, then plugs lines and pumps. The fix is simple:

  • Store it indoors, or heat-trace and insulate outdoor tanks and feed lines.
  • Keep it above ~60°F and it stays a clean, pumpable liquid.
  • Diluting caustic gives off heat — add caustic to water slowly, never the reverse.

Common questions

Why did my caustic turn to slush?
It got too cold. 50% caustic crystallizes in the mid-50s°F. Heat-trace and insulate the tank and lines, or move it indoors.
Viton or EPDM gaskets?
EPDM for caustic — one of the few cases where it beats Viton. PVC fittings, 316 stainless bolts.
Is it hard on poly tanks?
No — caustic is gentle on polyethylene. The whole game is temperature, not corrosion.

Sodium Hydroxide (Caustic) storage tanks from OneSource

For sodium hydroxide (caustic) storage, specify HDLPE_OR_XLPE rated to specific gravity 1.9. Verified, compatibility-matched options:

Confirm chemical compatibility and a ZIP freight quote with our team at 866-418-1777.

Sources & References

All compatibility ratings, hazard classifications, and chemical identifiers on this page are sourced from authoritative third-party publications. Verify against the original references before final specification.

  1. PubChem Compound Database — entry for Sodium Hydroxide (CID 14798, CAS 1310-73-2). pubchem.ncbi.nlm.nih.gov. National Library of Medicine / NCBI. Canonical chemical-identity reference.
  2. Snyder Industries Chemical Resistance Recommendations — system-of-construction guidance for polyethylene chemical-storage tanks at industrial ASTM 1.9 SG design rating. SNY-3041 Chemical Resistance Chart. Snyder Industries, current edition. Resin + fitting + gasket + bolt MOC matrix.
  3. Equistar Technical Tip — Chemical Resistance of Polyethylene — LDPE / MDPE / HDPE rating chart by concentration and temperature, distributed by Enduraplas. enduraplas.com (PDF). Equistar polyethylene resin chemical-resistance data, distributed via Enduraplas.
  4. NFPA 704: Standard System for the Identification of the Hazards of Materials for Emergency Response. nfpa.org. NFPA 704 'fire diamond' health/flammability/instability/special-hazard rating system (0–4 scale).
  5. UN Globally Harmonized System of Classification and Labelling of Chemicals (GHS), current revision. unece.org/transport/ghs. GHS pictograms, signal words, and H-statement codes referenced in this guide.
  6. ASTM D1998 — Standard Specification for Polyethylene Upright Storage Tanks, current edition. astm.org. Cited as the design-specific-gravity standard (typically 1.9 SG) for industrial chemical-service polyethylene tanks.
  7. NIOSH Pocket Guide to Chemical Hazards — occupational exposure limits, PPE, and IDLH data for Sodium Hydroxide. cdc.gov/niosh/npg. CDC / NIOSH chemical-specific occupational-safety reference.

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