The following are the minimum requirements that apply for the design of the Blowout Preventer control unit for the surface BOP, and it is of course, helpful in the rig inspection & acceptance of the BOP Control Unit:
- For annular preventers, the closing time should not exceed 30 sec for sizes smaller than 18 3/4″ nominal bore and 45 sec for those of 18 3/4″ and more significant.
- Hydraulic operating equipment shall have at least a 3,000 psi BOP accumulator unit equipped with two regulator valves, one to reduce the operating fluid pressure to 1,500 psi and the other for further pressure reduction for bag-type preventer operations.
- The accumulators’ capacity should equal the volume (V1) necessary to close and open all BOP functions installed on the stack at least once, plus 25% of V1. The liquid reserve remaining on accumulators should still be the minimum operating pressure of 1,200 psi (200 psi above the precharge pressure).
- The control panel shall be fitted with visual and acoustic alarms for signaling low accumulator pressure and control fluid reservoir low level.
- A minimum of two air-driven pumps and one electrically driven triplex pump are required for charging the accumulators. The combination of air and electric pumps shall be capable of charging the entire accumulator system from the precharge to full charge pressure within 15 minutes or less.
- In addition to the hydraulic master control panel, the BOP control unit shall include at least one graphic remote control panel located on the rig floor near the Driller’s console (Check also Driller Job Descriptions). Off-shore units shall have an additional graphic remote control panel located at a safe distance from the rig floor, usually in the tool pusher‘s office or adjacent to the escape route from the drilling unit. Each remote control panel shall be connected to the control manifold so that all functions can be operated independently from each panel.
- A safety device shall be installed on the BOP control manifold and remote panels to prevent accidental operations of BOP controls, such as the closure of the preventer rams (pipe or shear) on the drilling string while drilling or tripping pipe.
- The BOP end of the control hoses must be flexible and fireproofed.
- The BOP accumulator electric-driven pump shall be connected to an emergency power source.
Purpose of The Rig Inspection Of BOP Control Unit.
Verify the functionality of all the components of the BOP control unit (hydraulic and electro-hydraulic), the alarms, the pressure integrity of control lines, etc.
The Procedures Of The Rig Inspection Of BOP Control Unit
- Follows the Drilling Contractor test procedures for the BOP control unit.
- For each control element, test functionality and response.
- Repeat tests with all surface control panels (main and remote)
- Pressure test control hoses.
- Attach to the report the drawing of the BOP stack and surface control system schematic with the references for all components tested along with the results of tests.
Rig Inspection of the Accumulator Bottles
- Bleed off the pressure manifold of the accumulator Unit in the BOP Control Unit.
- Check precharge accumulator pressure to be by systems specifications.
Rig Inspection For Recharging time test.
- With accumulator pressure bled off to zero, start recharging with the electrical pump and record the time to reach 3000 PSI.
- Repeat the same test using air pumps only.
- Record the following
- All bottles are Precharged at …… psi.
- Number of bottles with wrong precharge No
- Recharging time with electrical pumps. min
- Recharging time with air pumps.
Other Items To Be In Mind While Inspecting Well Control System Prior Of Installation
- The control unit, before installation, should be tested for precharge pressure. The bottom valves of accumulator bottles should be opened, and all fluid drained off the reservoir. Check the nitrogen precharge pressure on each accumulator bottle; if required, it should be charged to the recommended pressure. This should be done after changing to a new drill site.
- Check reservoir fluid to be free from any foreign material or for bacterial growth. Change reservoir fluid if required.
- Pressure-clean all the lines before installation.
- Check for leakage from the diaphragm and change if required.
- Check the air lubricator. Clean and fill up with the manufacturer’s recommended lubricating oil.
- Check the remote control interface’s seal rings, air passage ports, and interconnect cable assembly for any damage and plugging.
- The control unit should be tested each time when the BOPs are tested. It should be done before pressure testing the BOP stack. The test should be conducted with a drill pipe lowered in the stack as follows :
- Record initial accumulator pressure and regulate operating pressure to annular preventer to 53 kg/cm2 (750 psi).
- Switch off the power supply to all pumps.
- Close the annular preventer and one ram BOP on the pipe. Open the hydraulically operated choke valve ( Check also: Choke Manifold). All this should be done simultaneously.
- Record time required to close annular and ram BOPs as stated above and in the opening of the hydraulic valve.
- Record final accumulator pressure. This should be at least 14.06 kg/cm2 (200 psi) above the precharge pressure.
