As offshore oil, gas and mining operations continue to expand in our never ending quest for energy, the need to transport fuels, liquids and gasses in a safe and efficient manner will also increase. This calls for heavy-duty chemical tanks built to contain all types of fluids in demanding offshore conditions.
Rigid Construction
Today’s chemical tanks must conform to the stringent construction guidelines established by the International Maritime Dangerous Goods (IMDG) Code and the US Department of Transportation (DOT). Moreover, chemical tank crash frame and base structures are now fabricated in accordance with the international DNV 2.7-1 standard, and some chemical tank designs must also meet rigid International Organization for Standardization (ISO) guidelines.
Tough Standards
The global offshore industry has adopted DNV 2.7-1 as the primary construction standard for Cargo Carrying Units (CCUs). Developed in 1986 by Det Norske Veritas, a Norwegian standards organization, DNV 2.7-1 has been endorsed by the Lloyd’s Registry Group and the American Bureau of Shipping to ensure that offshore chemical tanks are safer and more durable than standard maritime chemical tanks. Most tank designs also adhere to the EN 12079 European standard which covers design, construction, testing, inspection and marking.
Chemical Tank Features
Typical offshore chemical tanks share these common features:
- Fluid temperature range of -20C to plus +55C
- Carbon steel frames
- Multi-coat paint schemes (zinc-rich epoxy primer and polyurethane enamel)
- Mild-steel galvanized walkway(s)
- Easily accessible safety relief valves
- Anti-slip steps
- Bottom (emergency) outlets
- Document boxes/pouches
- Dipstick (optional)
- Drip tray (optional)
- Electrical heating (optional)
- Fall arrestor (optional)
- Insulation (optional)
- Ladder (optional)
- Level gauge (optional)
- Lined/coated tank (optional)
- Flat mesh covers (optional)
- Spare connections (optional)
Use of Chemical Tanks
Any number of fluids and liquids can be shipped in chemical tanks, but the most common can be split into two general categories: chemicals and foodstuffs.
Chemicals might include:
- Corrosives (acids)
- Dyes and extracts
- Flammable liquids (gasoline, oil, ethanol, etc.)
- Non-potable water
- Oxidizing agents (acetone, peroxides, etc.)
- Waste products.
Foodstuffs might include:
- Additives
- Alcohol
- Juices
- Potable water
- Rendered fats
- Syrups
- Vegetable oils.
Fluid Transport Basics
It’s important to know a few basic facts about transporting chemicals in tanks. First, try to fill the tank to about 80% capacity, but never to 100% capacity; this allows room (often caused “ullage space”) for thermal expansion and evaporation during transport. If you plan to transport hazardous materials, use tanks specifically designed for that purpose, with no seams or openings below the fluid level; to discharge these tanks, siphoning pipes are used with pressure release valves and/or pumps.
Sizing
Chemical tanks come in a wide range of sizes and configurations but most fall in the range of 300 gallon (1036L) to 1057 gallon (4000L).
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