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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 either HDLPE or crosslinked polyethylene (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.

Caustic or alkaline service: pick a polymer or FRP that lasts.

Strong bases stress-crack the wrong materials. These guides cover the material-of-construction call for caustic and alkaline storage.

Explore: FRP & Fiberglass Tanks  ·  Double Wall Tanks  ·  Chemical Compatibility

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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