n-Heptane Storage & Tank Compatibility
Storing n-Heptane? Start Here
n-Heptane (CAS 142-82-5, C7H16) is a colorless, volatile aliphatic hydrocarbon solvent with a molecular weight of 100.20 g/mol. It is essentially insoluble in water (about 0.0003 percent) and floats, with a density near 0.684 and a boiling point around 209 °F. With a closed-cup flash point of roughly 25 °F, it is a flammable Class IB liquid whose vapors form explosive mixtures in air and can flash back along a vapor trail.
The same nonpolar character that makes n-Heptane an effective degreasing and extraction solvent also drives it into the molecular structure of polyethylene. Because of this permeation and swelling behavior, n-Heptane should be stored in metal: UL-142 carbon steel or 304/316 stainless steel. Static control is critical, so bond and ground every transfer point. The notes below summarize the chemistry and the material-of-construction decisions for safe long-term storage.
Why Polyethylene Tanks Are Not Suitable for n-Heptane
Polyethylene tanks are excellent for water-based and many corrosive chemical services, but they are the wrong choice for n-Heptane. As a nonpolar aliphatic hydrocarbon, n-Heptane is absorbed into the polyethylene matrix, where it permeates the wall and causes the resin to swell and soften over time. This degrades wall strength, distorts fittings, and lets vapor migrate through the tank wall.
Cross-linked polyethylene (XLPE) is more resistant than standard HDPE, but cross-linking only slows hydrocarbon permeation; it does not stop it. For this reason both HDPE and XLPE are rated Unsuitable (U) for n-Heptane storage. The correct construction is steel: UL-142 carbon steel tanks built for flammable liquids, or 304/316 stainless steel where extra corrosion margin is wanted. Pair the tank with PTFE or Viton (FKM) seals and a complete bonding and grounding system.
Material compatibility at a glance
Store n-Heptane in UL-142 carbon steel or 304/316 stainless steel. Polyethylene (HDPE and XLPE) is not suitable because the aliphatic hydrocarbon permeates and swells the resin. Bond and ground all equipment, and use PTFE or Viton (FKM) seals.
| Material | Rating | Note |
|---|---|---|
| Tank Material | S | Notes |
| HDPE (high-density polyethylene) | U | Aliphatic hydrocarbon permeates and swells the polymer; not suitable for storage. |
| XLPE (cross-linked polyethylene) | U | Cross-linking slows but does not stop hydrocarbon permeation and softening; not suitable. |
| UL-142 carbon steel | C | Standard construction for flammable hydrocarbon solvents; bond and ground the tank. |
| 304 stainless steel | C | Compatible; resists the solvent with no degradation. |
| 316 stainless steel | C | Compatible; preferred where added corrosion margin is wanted. |
| PTFE / FEP fluoropolymer | C | Fully resistant; used for gaskets, liners, and seals. |
| Viton (FKM) seals | C | Resistant to aliphatic hydrocarbons; a standard elastomer choice. |
| Buna-N (NBR) seals | C | Generally resistant to aliphatic hydrocarbons; verify grade with the seal supplier. |
Ratings: S suitable · C conditional / limited · U unsuitable. Verify against the cited resistance charts and your concentration/temperature before specifying.
The safety that actually matters
- Flammable Class IB liquid: keep away from heat, sparks, open flame, and hot surfaces. No smoking and no ignition sources in the storage area.
- Vapors are heavier than air and can travel to a distant ignition source and flash back; ensure adequate ventilation and vapor control.
- Bond and ground all tanks, piping, pumps, and transfer containers to prevent static discharge during filling.
- Use only metal tanks (UL-142 steel or 304/316 stainless). Do not store in polyethylene.
- Aspiration hazard (H304): may be fatal if swallowed and it enters the airways. Do not induce vomiting.
- Prolonged or repeated exposure can damage organs (H372/H373) and cause drowsiness or dizziness (H336); use proper PPE and respiratory protection.
- Very toxic to aquatic life (H400/H410): contain spills and prevent release to drains and waterways.
Common questions
- Can I store n-Heptane in a polyethylene tank?
- No. n-Heptane is an aliphatic hydrocarbon that permeates and swells polyethylene, weakening the wall and allowing vapor migration. Both HDPE and XLPE are rated Unsuitable. Use UL-142 carbon steel or 304/316 stainless steel instead.
- What is the best tank material for n-Heptane?
- UL-142 carbon steel built for flammable liquids is the standard choice. 304 or 316 stainless steel is also fully compatible and offers extra corrosion margin. Pair the tank with PTFE or Viton (FKM) seals.
- Is n-Heptane flammable?
- Yes. n-Heptane is a flammable Class IB liquid with a closed-cup flash point near 25 °F (NFPA flammability rating 3). Its vapors form explosive mixtures in air, so keep all ignition sources away and bond and ground every transfer point.
- What are the NFPA 704 ratings for n-Heptane?
- Per NOAA CAMEO Chemicals: Health 1, Flammability 3, Instability 0, with no special hazard symbol. It is incompatible with strong oxidizers.
How we build n-Heptane storage
n-Heptane is a flammable solvent that permeates polyethylene. It is built in listed steel or stainless, bonded and grounded.
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.
- NOAA CAMEO Chemicals - n-Heptane — NFPA 704 ratings (Health 1, Flammability 3, Instability 0), flash point 25 F, and incompatibility with strong oxidizers. cameochemicals.noaa.gov
- PubChem - Heptane (CID 8900) — Identity data: CAS 142-82-5, formula C7H16, molecular weight 100.20, and GHS classification. pubchem.ncbi.nlm.nih.gov
- NIOSH Pocket Guide - n-Heptane — Physical properties including water solubility (about 0.0003 percent) and exposure limits. www.cdc.gov
- U.S. Coast Guard CHRIS - Heptane — Physical data: density 0.6838, boiling point 209.1 F, melting point -131 F, vapor pressure 37.49 mmHg. cameochemicals.noaa.gov
- New Jersey RTK Hazardous Substance Fact Sheet - n-Heptane — Flammability, health effects, and handling guidance for n-Heptane (CAS 142-82-5). nj.gov
- OSHA Occupational Chemical Database - Heptane — Regulatory exposure limits and hazard summary for heptane. www.osha.gov