LPG & NGL Storage

Pressurized or refrigerated

Pressurized storage is simple to run and suits frequent, smaller movements. Refrigerated storage holds far more product per ton of steel but needs refrigeration compressors, boil-off handling and chilling of warm product before it goes in. Product moving from pressurized storage into a refrigerated tank, or onto a fully refrigerated ship, has to be chilled first.

Pressure vessels and safety systems

We store LPG in vessels built and stamped to ASME Section VIII and installed to NFPA 58. A pressure vessel is never filled to the top. A fixed maximum liquid level leaves vapor space so the liquid can expand on a hot day without the vessel going liquid-full, which would drive pressure up fast.

Large LPG inventories generally bring a site under OSHA Process Safety Management (29 CFR 1910.119) and the EPA Risk Management Program (40 CFR Part 68), with their hazard analysis, mechanical integrity and emergency response requirements. We review every new LPG program against those rules before the first receipt, and only place product where the site meets them.

• Pressure relief valves sized for fire exposure and tested on schedule
• Remotely operated emergency shutoff valves on liquid lines
• Fixed water spray or deluge to cool vessel shells in a fire
• Gas detection at loading points, pumps and compressors
• Bonding and grounding checked before every truck and railcar transfer

Propane, butanes and NGL mixes

Natural gas liquids arrive in two forms. Raw mix, often called Y-grade, is an unfractionated stream of ethane, propane, butanes and natural gasoline bound for a fractionator. Purity products leave the fractionator as separate grades: propane, normal butane, isobutane and natural gasoline. Each purity product is kept segregated, because a few percent of the wrong component changes vapor pressure and price.

Consumer propane in the US is usually sold to HD-5 specification under GPA 2140 and ASTM D1835: at least 90 percent propane and no more than 5 percent propylene. Commercial propane and butane-propane mixes have their own limits, and petrochemical buyers set their own purity specifications.

Odorization

LPG has almost no smell of its own. For consumer use it is odorized, usually with ethyl mercaptan, so a leak is noticed well before the gas reaches a flammable concentration: NFPA 58 requires detection at no more than one-fifth of the lower flammable limit. A commonly used dose is about 1.0 pound of ethyl mercaptan per 10,000 gallons.