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Thursday, December 22, 2011

Calculate Bottles Required for Koomey Unit (Accumulator Unit)

This topic will demonstrate you how to determine accumulator bottles required for Koomey Unit (Accumulator Unit) in order to close the BOP stack.

This is a specification of Accumulator (Koomey) Unit.

Accumulator 3,000 psi system

Volume each bottle is 10 gallon.

Pre charge pressure is 1,000 psi.

Minimum operating pressure is 1,200 psi (200 psi over pre charge pressure)

Usable fluid per gallon is 5 gallon.

Safety factor require is 50 %.


BOP Stack and HCR's as listed below:

 Equipment  Gallon to open  Gallon to close
 Annular Preventor  4.0  4.5
 Upper Pipe Rams  3.0  3.5
 Blind Shear Rams  3.5  4.0
 Lower Pipe Rams  3.0  3.5
 Choke HCR  0.5  0.5
 Kill HCR  0.5  0.5

Please follow the steps below for calculation

 1. Determine total volume require to close all of equipment

Volume = 4.5+3.5+4+3.5+0.5+0.5 = 16.5 gallon

2. Volume accounted for safety factor

Volume = 16.5 x 1.5 = 24.75 gallon

3. Determine numbers of accumulator bottles required to meet volume determined in step#2

Number of bottles = volume ÷ usable fluid per bottle

Number of bottles =24.75 ÷ 5 = 4.95 so you round it up to 5 bottles

In order to close all BOP as per requirement without any assistance of electric and pneumatic pumps, you need to have a total of 5 accumulator bottles.

You will see that based on the calculation above, determining required Koomey bottles is quite straight forward. Thing to remember is that you must use closing volume not opening volume. I see many people using the wrong figures. Even though it may not have big impact on the final result, you need to select the right figures for calculation. Moreover, the safety factor may be different based on the regulations of your working area or your company policy.

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