FlowSim 16D

1. Quick start

1. Choose the system with the tabs: Main BOP control unit (annular, rams, valves — optionally with a dedicated shear accumulator), Diverter accumulator or Pilot accumulator.
2. Click “New calculation” and work through the steps with Next →. The step bar at the top shows each step as needs data, complete or not used; click any step to jump to it.
3. BOP stack: add each function from the OEM datasheets with “+ Annular”, “+ Pipe ram” … Tick which functions are in the drawdown (Method B) and in the well-control sequence (Method C). Shear columns appear once a blind shear ram is added.
4. Operating conditions: enter the site temperatures, system (pump stop) pressure and bottle RWP. These project values have no default — FlowSim never assumes them.
5. Accumulators & pumps: confirm the bottle sizes and the charge-time limit. Pump and vendor data sit under “Equipment data and defaults”; the defaults are documented and can usually be kept.
6. Review & run: set a design precharge tolerance if you want one, then Run sizing. Anything missing is listed with a link to the field.
7. Results: the recommended bottle option is highlighted, with the precharge to set and its acceptable range, pumps and reservoir. “Defaults used” lists every default the calculation relied on.
8. Visual analysis (in the results): use the charts to inspect the selected design and run sensitivity when needed.
9. Save keeps the inputs as a project file; Print report produces a self-contained calculation record including the input data; Print Summary prints the summary tables with the design plots.

Your inputs are also kept in this browser as a draft, so a page refresh does not lose work. “New calculation” clears the draft.

2. Workflow

Each step lists the equipment it concerns, the data the engineer supplies and what FlowSim produces from it. The input steps come first; the last three are computed when you run the sizing.

Diverter and pilot accumulators follow the same flow with their own function list in step 2 (diverter functions; pilot valve volumes and pressures) and no dedicated shear circuit.

3. Calculation method

FlowSim converts the entered equipment data into the required hydraulic volume, minimum operating pressure, accumulator bank, pump selection and reservoir size. Pressures are entered as psig unless a field says otherwise; nitrogen properties are evaluated with a real-gas equation of state.

3.1 Sizing flow

3.2 Accumulator bank, pumps and reservoir

3.3 Visual analysis

Select the circuit and bottle option above the chart tabs. Use the charts to inspect precharge, volume, pump charging and sensitivity for the selected design.

4. Standards & references

4.1 API Spec 16D, 3rd Edition — Control Systems for Drilling Well Control Equipment

4.2 Thermophysical properties and methods

1. Span, R., Lemmon, E.W., Jacobsen, R.T, Wagner, W., Yokozeki, A. (2000). A reference equation of state for the thermodynamic properties of nitrogen for temperatures from 63.151 to 1000 K and pressures to 2200 MPa. Journal of Physical and Chemical Reference Data 29(6), 1361–1433. — nitrogen density and entropy used throughout.
2. Lemmon, E.W., McLinden, M.O., Friend, D.G. Thermophysical Properties of Fluid Systems. In: NIST Chemistry WebBook, NIST Standard Reference Database 69 (P.J. Linstrom, W.G. Mallard, eds.), National Institute of Standards and Technology.
3. Bell, I.H., Wronski, J., Quoilin, S., Lemort, V. (2014). Pure and pseudo-pure fluid thermophysical property evaluation and the open-source thermophysical property library CoolProp. Industrial & Engineering Chemistry Research 53(6), 2498–2508. — software implementation of the equation of state (HEOS backend).
4. Hydraulic power identity: hp = Q[gpm] · Δp[psi] / 1714, from 1 hp = 33,000 ft·lbf/min and 1 US gal = 231 in³.
5. Boyle's law (isothermal ideal gas, P·V = constant) — optional stored-fluid model and free-air conversion for air consumption.
6. NEMA standard motor ratings — default electric motor catalogue (5 to 100 hp).

5. Rules & defaults

Every factor the calculation uses, with its source. “Engineering practice” and “Project input” values are defaults you may change in the calculation; API 16D values are fixed by the method.

6. Assumptions & limitations

• Surface installations: operating pressures are not corrected for hydrostatic head (subsea stacks are out of scope).
• Method B expansion is isothermal; Method C, dedicated shear and (by default) diverter expansions are isentropic. Real discharges lie between these limits.
• Charging is slow and isothermal at the precharge temperature (stored fluid and pump charge time).
• Project values — site temperatures, system pressure, bottle RWP, regulator pilot pressure — must be entered; there are no defaults. Every other input has a documented default (section 5), and the report lists each default actually used.
• Pump power is evaluated at system pressure with suction at atmospheric pressure. Motor and engine ratings are shaft output; the pump efficiency sizes them, the motor efficiency only gives the electrical input.
• Each reservoir configuration uses the same bottle size in every circuit.
• Precharge gas is pure nitrogen; bladder volume changes and fluid compressibility are neglected.
• Usable bottle volumes are typical bladder-accumulator values — confirm with the manufacturer's datasheet.
• The air-pump stall-line model is first order; use the vendor performance curve for final selection.
• Adiabatic discharge cools the gas well below ambient (reported as an information check); the bladder and seal low-temperature rating is not checked automatically.
• The ideal-gas option exists for comparison only: nitrogen compressibility is 0.98–1.19 in the design range.

7. Glossary

ACR

Accumulator capacity required: the gas volume of the accumulator bank needed for a method, FVR / VE.

Acceptable precharge range

Precharge pressures (at the precharge temperature) for which the installed bottles still meet every method.

Charged condition

Accumulator at pump-stop (Method B) or pump-start (Method C, dedicated) pressure.

Closing / sealing / shearing ratio

Ratio of wellbore pressure to the hydraulic operating pressure needed to close, seal or shear against it.

Defaults used

Inputs left at their documented default value; listed with their source in every report so they can be confirmed.

Design charge time / margin

The charge time pumps are selected against: the API limit reduced by the design margin (default 10%).

Dedicated shear accumulator (DSR)

Accumulator circuit reserved for the blind shear ram, with its own pressure and pumps.

FVR

Functional volume requirement: hydraulic fluid the functions consume.

Isothermal / isentropic

Gas expansion at constant temperature (slow) or constant entropy (fast, no heat exchange — the gas cools).

Method B

Accumulator drawdown: all functions, isothermal.

Method C

Well-control sequence: the functions operated in the sequence, adiabatic, starting from pump-start pressure.

MOP

Minimum operating pressure: the lowest accumulator pressure at which the governing function still operates.

MOPFLPS

Minimum operating pressure for a function at zero wellbore pressure.

Precharge

Nitrogen pressure in the empty accumulator (bladder fully expanded) at the precharge temperature.

psig / psia

Gauge pressure / absolute pressure (psia = psig + atmospheric).

RWP

Rated working pressure — of the wellbore (stack) or of the accumulator bottles, as labelled.

Stall pressure

Outlet pressure at which an air-driven pump stops delivering: area ratio × air supply pressure.

VE

Volumetric efficiency: usable fluid per unit of accumulator gas volume (pressure- or volume-limited).

Z

Compressibility factor, P / (ρ R T); 1 for an ideal gas.