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Deck & Support Systems
Storage and Surge Tanks
Storage and surge tanks hold product between a rig's main bulk storage and the equipment that uses it. The Category covers cement and barite surge tanks, liquid storage tanks, and portable tanks for base oil, brine and chemicals. Main dry bulk tanks are under Bulk Storage Tanks, and mud pits under Drilling Fluid Systems.
What surge and storage tanks do
A surge tank is a small pressure vessel, often on legs above the cement unit or mixing hopper. It takes a batch of powder from the main bulk tanks, lets the transport air vent off through a dust collector, and then feeds the powder by gravity or low-pressure air at a steady rate. A steady feed gives the mixer a consistent slurry or mud weight.
Liquid storage tanks hold base oil, brine, drill water and chemicals. Portable versions in frames let a rig take on special fluids for one well and send the empty tanks back.
Configurations
| Type | Pressure | Typical use |
|---|---|---|
| Cement surge tank | Pressure vessel | Feeds the cement unit |
| Barite or bentonite surge tank | Pressure vessel | Feeds mud mixing hoppers |
| Fixed liquid tank | Usually atmospheric | Base oil, brine, chemicals |
| Portable liquid tank | Atmospheric or pressure | Campaign fluids, swapped by crane |
| IMO portable tank | Rated to IMDG chapter 6.7 | Dangerous goods |
Key specifications
| Parameter | Why it matters | Typical classes or units |
|---|---|---|
| Working capacity | A surge tank must hold a useful batch for the unit it feeds | ft³ or m³, bbl for liquids |
| Design pressure and code | Sets inspection and repair route | bar (psi), ASME VIII Div 1 |
| Vent and relief sizing | Must pass the full transfer air flow | mm (in), set pressure |
| Material or lining | Must resist the product | Carbon steel, stainless, coated |
| Weighing or level | Feeds your control system | Load cells, radar or float gauges |
| Frame rating | For portable tanks | Gross mass in t (lb) |
Standards and certification
Pressurised surge tanks follow ASME Section VIII Division 1, PED or the class society's pressure vessel rules. A portable tank lifted offshore also needs an offshore container certificate to DNV-ST-E271 or an equivalent standard, and its lifting set inspected on that standard's schedule.
A portable tank for dangerous goods needs IMDG Code approval. It needs a periodic inspection with a hydraulic pressure test at least every 5 years, and an intermediate inspection and test every 2.5 years between them. The intermediate test can be done up to 3 months either side of its due date. A tank that has missed either test cannot be filled and offered for transport until it passes a new 5-year test. The dates are on the tank's data plate.
Failure modes and inspection
- Surge tanks. Check the data plate, design pressure and test record, then inspect inside for hard cement. Dust collector filters and vent lines block easily, and a blocked vent can overpressure the tank during transfer.
- Relief valves. Check the set pressure certificate and that the valve suits the transfer air flow.
- Load cells. Batch weighing needs current calibration.
- Liquid tanks. Look for lining or coating breakdown, shell pitting, and leaking gaskets, valves and manways.
- Frames. Run magnetic particle inspection on pad eyes and frame welds.
Documentation
- Code documents and data plate details
- Hydrostatic test and relief valve certificates
- Last internal inspection and thickness readings
- Offshore container certificate and lifting set records
- IMDG approval and test dates for dangerous goods tanks
- Previous cargo list and cleaning certificates
Integration and compatibility
Size a surge tank to the cement unit or hopper it feeds, and match the inlet from your bulk line and the outlet to the mixer. Route its vent and dust collector to a safe discharge point. For liquid tanks, check outlet connections, any heating or agitation power, and that the lining suits your fluid.
Refurbishment and recertification
Refurbishment usually covers cleaning, relining or recoating, new gaskets and valves, relief valve recertification and a hydrostatic test, plus the IMDG periodic test where it applies. Previous cargo decides the cleaning needed, and a tank that held oil-based fluids or chemicals needs certified cleaning before water or brine service. A used surge tank fits well when it matches your cement unit and piping. Unused surplus tanks with full documents avoid the cargo question. Upstream, see bulk storage tanks. For active and reserve mud pits, see mud mixing and storage.
FAQ
Frequently asked questions
What does a cement surge tank do on a drilling rig?
A cement surge tank holds a batch of dry cement just above the cement unit and feeds it at a steady rate. The transfer air from the bulk tanks vents off in the surge tank, so the unit can mix a consistent slurry density.
How often do IMO portable tanks need to be tested?
An IMO portable tank needs a periodic inspection and hydraulic pressure test at least every 5 years, and an intermediate inspection and test every 2.5 years in between. The intermediate test has a 3-month window either side of its due date. The dates are on the tank's data plate.
What happens if a portable tank misses its 2.5-year test?
It cannot be filled and offered for transport until it passes a new 5-year periodic inspection and test. Under the IMDG Code, that 5-year test replaces the missed intermediate one and restarts both intervals.
Should I ask about previous cargo when buying a used storage tank?
Yes. Previous cargo decides how much cleaning the tank needs and whether its lining and seals suit your product. A tank that held chemicals or oil-based fluids may need certified cleaning before it can hold drill water or brine.
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