Doe tri lab assessment of bp flange connector spool 3 ram capping stack
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Doe tri lab assessment of bp flange connector spool 3 ram capping stack

DOE Tri-Lab Assessment of BP Flange Connector Spool & 3 Ram Capping Stack

This report was created at the request of the Department of Energy in support the Deepwater Horizon incident technical response efforts.  The report is unclassified.   BP asserts that the information supplied in preparation of this report is approved for unlimited release and Sandia knows of no impediment to such an unlimited release of this report.     The report reflects the best information available at the time of its preparation and was a collaborative effort among a number of different institutions.

June 26, 2010

Lawrence Livermore National Laboratory

1


Assessment report outline

Assessment Report Outline

  • This report will follow the same outline as the Flange Connector Spool Assembly and 3 Ram Capping Stack Design Review which was held at BP on June 23, 2010

    • Overview of Design

    • Engineering of Combined Stack

    • Review of Flex Joint (+ Transition Spool & Mud Boost Valve)

    • Instrumentation and Control

    • Installation Techniques and Testing

  • Following the observations and comments in each technical area, we will include:

    • DOE Tri-Lab Team Findings and Recommendations

    • Summary

2


Overview of design

Overview of Design

  • Various worst case loads were considered; not all possibilities were presented (they are available and should inserted into the record); we conclude that the likely load case space has been adequately explored.

  • Recommendation #1: Ensure that an analysis of the allowable worst case combination of loads (eg. largest tilt, highest temperature, highest pressure) is included in the record.

  • It should be noted that the margins of the design are highly sensitive to differential pressure

  • Recommendation #2: Measures should be taken to limit maximum pressure during well integrity testing and well shut-in operations.

    • Limiting valve closing increments

    • Limiting rates of closure and thereby limiting maximum pressure

3


Overview of design cont d

Overview of Design (Cont’d)

  • The current design as shown will be adequate given the expressed limits on loading conditions (maximum 5.5 degree flex joint total tilt, etc.).

    • Requires lateral support of flex joint

    • Finding #1: – BP must monitor the tilt of the combined stack to ensure that the induced load limit is never exceeded

  • Recommendation #3: Given the many possible loading conditions, supporting analysis capability should remain engaged to quickly evaluate actual operational conditions as events unfold.

  • The proposed pressure and temperature instrumentation are adequate and provide sufficient redundancy for the criteria of a single pressure measurement.

4


Overview of design cont d 2

Overview of Design (Cont’d 2)

  • Installation techniques and testing as presented appear feasible and realistic but this work is ongoing and warrants additional review and evaluation.

  • Recommendation #4: Although not presented during the design review, BP’s evaluation of the ability of all added components to withstand the maximum expected internal pressure should be included for the record (eg. as-built documentation to ensure proper bolt pre-load).

  • These conclusions are also based on the stated three-month design life; if operation of this equipment extends beyond this time then other issues of corrosion, fatigue, etc. will require investigation and evaluation.

5


Engineering of combined stack

Engineering of Combined Stack

  • The beam element FE global model for the total stack is appropriate to determine overall deflections & applied moments.

  • Recommendation #5: An elastic/plastic finite element model should be run to predict ultimate failure mode and pressure of the stack system (eg Flex Joint, G Flange and Transition Spool).

  • Connectors & casing strings were evaluated under worst case load combinations and found to be acceptable with generous design margins remaining.

  • Finding #2: Since overpressure can lead to catastrophic failure, the selection of the burst disk must be approved by the DOE team.

6


Engineering of combined stack cont d

Engineering of Combined Stack (Cont’d)

  • G-class flange (the flanges joining the flex joint and the flex joint connector spool) limitations are the connecting bolts.

    • Finding #3: Detailed bolt analysis (material property, preload and torque information, etc.) was not presented - only individual bolt load capability was available. This information must be provided and inserted into the record.

    • Assuming the stated 500 kips load capability per bolt is valid, at least two bolts are available to carry the moment, the flex joint is restrained to a 5.5 degrees or less total tilt and the differential pressure is limited to 6750 psi, the joint should be adequate.

      • If any of these qualifying conditions are not met, then the adequacy of this flange connection is in question.

    • Recommendation #6: a calculation should be performed prior to installation in order to determine the effect of having five or fewer bolts restraining the flange and/or increased differential pressure.

7


Review of flex joint

Review of Flex Joint

  • Oil States Inc. (OSI), manufacturer of the flex joint, presented design, analysis, and testing of the current flex joint, as well as extensive field experience based upon 30+ years of fabricating designs that rely on similar spherically-shaped laminated elastomeric bearings.

  • OSI presented detailed finite element analyses that included appropriate constitutive elements (elastic- plastic elements for metal components and hyper-elastic elements for elastomeric components)

    • Model results indicated no leakage under worst case conditions

8


Review of flex joint cont d

Review of Flex Joint (Cont’d)

  • The use of restraining shims to limit tilt will nullify the original capabilities of the flex joint to accommodate drilling riser and drill string movement

    • Recommendation #7: Connection of the combined BOP stack to collection operations vessels on the surface should recognize new limitations in the Flex Joint.

  • Recommendation #8: Use of shims to limit rotation of the flex joint will alter the load path and requires further analysis (including installation loads on bolts) prior to installation.

  • Future operations that could exceed the assumed loads must be analyzed prior to application.

9


Review of transition spool

Review of Transition Spool

  • Transition spool design is stressed beyond standard engineering practice (to 90% of yield strength) under several of the presented loading cases; the compressive loading case is noted as being especially conservative. However, the stated limits on stack tilt will effectively lower the stress but not to within normal engineering practice (typically 2/3 of tensile yield strength).

    • It is noted that the adequacy of this component is highly sensitive to differential pressure.

  • Finding #4: Since the Transition Spool is expected to be stressed near yield, BP must either present relevant quality data (material certification / inspection records and manufacturing) for the as-built component, or perform proof testing to demonstrate margin.

10


Review of mud boost valve

Review of Mud Boost Valve

  • Mud Boost face seal has a potential leak vulnerability

  • Bolt pre-load is estimated to be overcome at 6600 psig

  • Variations in bolt installation pre-load could reduce this pressure

  • O-ring damage may occur if bolt pre-load is overcome

    • This could result in a persistent leak

  • Recommendation #9: Installed bolt torque should be confirmed, if possible via documentation of the as-built configuration.

  • Recommendation #10: BP should observe to watch for leaks during any high pressure operation.

  • Recommendation #11: In addition, BP should consider injecting a pressure sensitive sealant into the Mud Boost valve in order to reduce the possibility of leakage at the flange.

11


Instrumentation and control

Instrumentation and Control

  • Doubly redundant pressure measurement below the 3 Ram Capping Stack (mini-BOP) is appropriate to meet data requirements

  • Recommendation #12 - Generate a complete system level analysis of the estimated accuracy of pressure measurement

  • Recommendation #13 - Once a correlation between the three pressure measurements (at several different pressures) is made, transmit only one of the three pressure measurements so that higher frequency sampling rate can be obtained.

    • Sampling of a single gauge should be done at a rate of at least once every 5 seconds.

    • We recommend sampling the three gauges nominally once every 15 minutes to confirm there is no drift.

12


Installation techniques testing

Installation Techniques & Testing

  • Story boarding and land/pool testing is a best practice of great value and should continue.

  • Recommendation #14: Attention should be given to potential bolt issues during riser flange removal and FCS installation such as tool access/engagement, possible need for captive nut replacement, and alternate means of providing flange clamping force.

  • Planned chop saw approach for cutting riser from a variety of angles appears to be a robust approach and should be pursued.

  • No attempt should be made to extract either of the drill pipes unless circumstances are significantly altered by future events. Review will be required at such time.

13


Installation techniques testing cont d

Installation Techniques & Testing (Cont’d)

  • Consider using the “plume-inator” during FCS installation to improve the view of the drill pipes.

  • Applied forces should be monitored (e.g. hydraulic ram pressure) and the operation halted if required levels approach limits of analyzed load cases.

    • Following hydraulic jacking to straighten Flex Joint, any deviations from the expected stiffness values should be investigated.

  • Selection of the maximum pressure during well integrity testing should consider Mud Boost Face seal limitations.

  • Finding 5: Details on methanol injection were not provided during the review. These must be provided to the DOE team.

14


Review team findings

Review Team Findings

  • Finding #1: – BP must monitor the tilt of the combined stack to ensure that the induced load limit is never exceeded

  • Finding #2: Since overpressure can lead to catastrophic failure, the selection of the burst disk must be approved by the DOE team.

    • Finding #3: Detailed bolt analysis (material property, preload and torque information, etc.) was not presented - only individual bolt load capability was available. This information must be provided and inserted into the record.

    • Finding #4: Since the Transition Spool is expected to be stressed near yield, BP must either present relevant quality data (material certification / inspection records and manufacturing) for the as-built component, or perform proof testing to demonstrate margin.

    • Finding #5: Details on glycol injection during installation were not provided during the review. These must be provided to the DOE team.

  • 15


    Review team recommendations

    Review Team Recommendations

    • Recommendation #1: Ensure that an analysis of the allowable worst case combination of loads (eg. largest tilt, highest temperature, highest pressure) is included in the record.

    • Recommendation #2: Measures should be taken to limit maximum pressure during well integrity testing and well shut-in operations.

    • Recommendation #3: Given the many possible loading conditions, supporting analysis capability should remain engaged to quickly evaluate actual operational conditions as events unfold.

    • Recommendation #4: Although not presented during the design review, BP’s evaluation of the ability of all added components to withstand the maximum expected internal pressure, should be included for the record (include as-built documentation to ensure proper bolt pre-load).

    16


    Review team recommendations cont d

    Review Team Recommendations (Cont’d)

    • Recommendation #5: An elastic/plastic finite element model should be run to predict ultimate failure mode and pressure of the stack system (eg Flex Joint, G Flange and Transition Spool).

    • Recommendation #6: a calculation should be performed prior to installation in order to determine the effect of having five or fewer bolts restraining the G-flange and/or increased differential pressure.

      • Recommendation #7: Connection between the combined BOP stack to collection operations vessels on the surface should recognize new limitations in the shimmed Flex Joint.

      • Recommendation #8: Use of shims to limit rotation of the flex joint will alter the load path and requires further analysis (including installation loads on the bolts) prior to installation.

    17


    Review team recommendations cont d 2

    Review Team Recommendations (Cont’d 2)

    • Recommendation #9: Installed bolt torque on Mud Boost valve flange should be confirmed, if possible via documentation of the as-built configuration.

    • Recommendation #10: BP should monitor for leaks around the Mud Boost valve flange during any high pressure operation.

    • Recommendation #11: In addition, BP should consider injecting a pressure sensitive sealant into the Mud Boost valve flange in order to reduce the possibility of leakage at the flange.

    • Recommendation #12: Generate a complete system level analysis of the estimated accuracy of pressure measurement

    18


    Review team recommendations cont d 3

    Review Team Recommendations (Cont’d 3)

    • Recommendation #13: Once a correlation between the three pressure measurements is made, transmit only one of the three pressure measurements so that higher frequency sampling rate can be obtained.

    • Recommendation #14: Attention should be given to potential bolt issues during riser flange removal and FCS installation such as tool access/engagement, possible need for captive nut replacement, and alternate means of providing flange clamping force.

    19


    Summary

    Summary

    • A comprehensive, four hour review was held by BP on June 23, 2010 at which the design, analysis and testing of the Flange Connector Spool Assembly and 3 Ram Capping Stack were presented.

    • Reviewers included Subject Matter Experts from the three DOE design Labs as well as two DOE Science Advisors.

    • Five Findings have been identified that the DOE Review Team feel must be closed before installation.

    • Fourteenrecommendations were generated that should increase our collective confidence in the proposed design, installation, and operation.

    • The review did not generate any concerns that would warrant design modifications at this time.

    A number of components have limited design margin, therefore BP must ensure that established limiting conditions (such as tilt angle and internal pressure) are never exceeded

    20


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