Ortho-Xylene (o-Xylene) Storage & Tank Compatibility

Storing Ortho-Xylene (o-Xylene)? Start Here

Ortho-xylene (o-xylene, 1,2-dimethylbenzene, CAS 95-47-6) is an aromatic hydrocarbon solvent with the formula C₈H₁₀ and a molecular weight of 106.16 g/mol. It is a colorless, water-insoluble liquid that is less dense than water (density about 0.88) and boils between 289 and 293 °F. As a flammable liquid with a flash point near 63 °F, its vapor is heavier than air and can travel to an ignition source and flash back, which drives its NFPA flammability rating of 3.

The defining storage problem is not corrosion but solvency: like other xylene isomers, toluene, and ethylbenzene, ortho-xylene attacks polyethylene. The small aromatic molecule permeates HDPE and XLPE tank walls and causes the resin to swell and soften over time. For that reason polyethylene tanks are not a suitable material of construction. Bulk ortho-xylene is properly stored in 304 or 316 stainless steel or in UL-142 listed carbon steel, with FKM (Viton) seals rather than EPDM.

Why Polyethylene Tanks Are Not Suitable for Ortho-Xylene

Polyethylene resists most aqueous acids, bases, and salt solutions, but it does not resist aromatic hydrocarbon solvents. Ortho-xylene is a non-polar aromatic that is chemically similar to the polyethylene chain, so it readily dissolves into the polymer matrix. Two failure modes follow. First, the solvent permeates through the tank wall, so the tank loses product as vapor and the surrounding area accumulates a flammable atmosphere. Second, absorbed solvent swells and softens the wall, reducing stiffness and burst strength and accelerating environmental stress cracking.

Published HDPE chemical-resistance guides rate xylene as unsatisfactory (U) at both ambient and elevated temperatures. Cross-linking (XLPE) improves stress-crack resistance but does not block aromatic permeation or swelling, so XLPE is also rated unsuitable. The correct answer is a metal tank. For ortho-xylene service, specify 304 or 316 stainless steel or a UL-142 listed steel tank built for flammable aromatic hydrocarbons.

Material compatibility at a glance

Store ortho-xylene in metal: 304 or 316 stainless steel or UL-142 listed carbon steel. Polyethylene tanks (HDPE and XLPE) are not suitable because this aromatic solvent permeates and swells the resin. Use FKM (Viton) elastomers for seals; avoid EPDM.

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 liquid (NFPA Flammability 3, flash point about 63 °F): keep away from heat, sparks, open flame, and hot surfaces; no smoking; ground and bond containers during transfer.
• Vapor is heavier than air and can travel to a remote ignition source and flash back; provide low-level ventilation and use intrinsically safe electrical equipment.
• Health hazards include skin and eye irritation, respiratory irritation, drowsiness and dizziness, and possible organ damage; o-xylene may be fatal if swallowed and enters the airways (aspiration hazard).
• Use chemical splash goggles, solvent-resistant gloves, and adequate respiratory protection; avoid breathing vapor or mist.
• Toxic to aquatic life with long-lasting effects; prevent release to drains, soil, and waterways and provide secondary containment.
• Store in approved metal tanks (stainless or UL-142 steel) with FKM seals; never store in polyethylene.

Common questions

Can I store ortho-xylene in an HDPE or XLPE poly tank?

No. Ortho-xylene is an aromatic hydrocarbon solvent that permeates and swells polyethylene. Both HDPE and XLPE are rated unsuitable for xylene, so polyethylene tanks are not an appropriate material of construction. Use stainless or UL-142 steel instead.

What tank material should I use for ortho-xylene?

Use metal: 304 or 316 stainless steel, or a UL-142 listed carbon steel tank built for flammable aromatic hydrocarbons. Pair the tank with FKM (Viton) seals rather than EPDM, which swells in aromatics.

What is the NFPA 704 rating for ortho-xylene?

Per NOAA CAMEO Chemicals, ortho-xylene is rated Health 2, Flammability 3, and Instability 0, with no special hazard. The Flammability 3 reflects a flash point near 63 °F.

Is ortho-xylene flammable?

Yes. Ortho-xylene is a flammable liquid with a flash point around 63 °F. Its vapor is heavier than air and can travel to an ignition source and flash back, so it must be stored away from heat and ignition sources with proper bonding and grounding.