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Bulk Storage Tanks
Bulk storage tanks hold the dry powders a drilling unit uses in volume, mainly barite, bentonite and cement. They are pneumatic pressure vessels, so compressed air can push the powder out to surge tanks and mixing systems. The Category covers fixed rig tanks and skid-mounted portable tanks in frames, with their aeration systems, valves and load cells.
How a pneumatic bulk tank works
The supply vessel blows powder up a hose into the tank, and the transport air leaves through a vent and dust collector. To discharge, you close the vent and pressurise the tank. Air fed through aeration pads or a fluidising section in the cone loosens the powder so it flows out of the bottom outlet, along the discharge line to a surge tank. When the tank is empty, the air is vented and the tank is ready to fill again.
Fixed tanks are usually tall vertical vessels in the hull, columns, pontoons or legs, depending on the rig type. Portable tanks sit in a lifting frame so the rig can swap them by crane.
Configurations
| Type | Where it sits | Main trade-off |
|---|---|---|
| Fixed vertical tank | Hull, column or deck structure | Large volume, very hard to remove |
| Portable tank in frame | On deck, swapped by crane | Flexible, but needs offshore lifting certification |
| Cone-bottom tank | Either | Empties well, taller for its volume |
| Aerated flat or shallow-cone tank | Either | Lower profile, depends on aeration condition |
Tanks are usually dedicated to one product. Cement and barite tanks are not interchangeable without full cleaning.
Key specifications
| Parameter | Why it matters | Typical classes or units |
|---|---|---|
| Volume | Sets how much bulk the rig carries | ft³ or m³ |
| Design pressure and temperature | Must exceed your air system's discharge pressure | bar (psi), °C (°F) |
| Design code | Decides how you inspect and repair it | ASME VIII Div 1, PED, class rules |
| Outlet and line bore | Sets transfer rate | mm (in) |
| Weighing | Inventory control | Load cells, range in t (lb) |
| Frame and gross mass | For portable tanks, sets crane and certification | t (lb), DNV-ST-E271 |
Standards and certification
The data plate and the manufacturer's data report prove the design code, pressure rating and original hydrostatic test. A US-built vessel with a National Board number can be traced through its registration. Relief valves need a current set pressure certificate. On a classed rig, the tanks appear in the class survey records. A portable tank's frame, pad eyes and lifting set follow DNV-ST-E271 or a similar offshore container standard.
Failure modes and inspection
- Caked product. Hardened cement or barite on walls and in the cone traps moisture and hides corrosion.
- Corrosion under deposits. Common in the cone and near the aeration inlets.
- Erosion. Barite is abrasive, so check outlets, elbows and the first bends of the discharge line.
- Aeration. Look for torn, blinded or missing pads and blocked air inlets.
- Valves. Butterfly and plug valves on the discharge wear at the seat and leak.
- Wall thickness. Ultrasonic readings across the shell, cone and nozzles show the metal left against the minimum required by the code.
- Frame. On portable tanks, run magnetic particle inspection on pad eyes and frame welds.
Internal inspection is a confined-space entry, so plan gas testing and access before the survey.
Documentation
- Data plate, manufacturer's data report and National Board registration if any
- Hydrostatic test history and relief valve certificates
- Thickness survey and internal inspection reports
- Class survey entries for fixed tanks
- Offshore container certificate and lifting set records for portable tanks
- Load cell calibration records
Integration and compatibility
Match the design pressure to your air supply, and check that your air dryer gives a low enough dew point. Moist air is the commonest cause of caking. Check fill, vent and discharge connections against your piping, and wire load cells into your bulk monitoring system.
Refurbishment and recertification
Typical refurbishment covers cleaning, new aeration pads and gaskets, valve overhaul, internal coating, relief valve recertification and a new hydrostatic test. Any welded repair to the pressure envelope follows the original code, or NBIC for ASME vessels. Used portable tanks with a recent hydrostatic test and lifting certificate are a common purchase. Unused surplus tanks from cancelled newbuilds suit if the code documents came with them. Downstream, see storage and surge tanks. The fill hoses are under fluid transfer hoses.
FAQ
Frequently asked questions
What should I check on a used barite or cement bulk tank?
Check the data plate, manufacturer's data report, hydrostatic test history and relief valve certificates first. Then inspect inside for caked product, corrosion under deposits and damaged aeration pads, and ask for ultrasonic thickness readings across the shell, cone and nozzles.
Can a bulk tank used for cement be switched to barite?
Usually yes, after full cleaning. Both are dry powders moved by air, but cement residue sets with moisture and would contaminate mud. Check that the aeration system and discharge line suit the denser barite, and that the load cells and structure allow for the heavier contents.
How is a used bulk tank pressure tested?
A bulk tank is hydrostatically tested by filling it with water and raising it to the test pressure set by its design code. The inspector then checks for leaks and permanent deformation. Dry the tank fully afterwards, because any moisture left inside will cake the first load of powder.
Do portable bulk tanks need DNV 2.7-1 certification?
Most offshore lifts require it or an equivalent standard. DNV-ST-E271 (DNV 2.7-1) covers the frame, pad eyes and lifting set of offshore containers. The pressure vessel itself is certified to its own code, so a portable tank needs both certificates.
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