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JIP Phase 1 1. Phase 1 Objectives 2. Phase 1 CTRs 3. Awareness document 4. Aero-elastic interaction 5. Questionnaire 6. Offshore measurements 7. Acoustic simulation 8. Scale testing 9. Numerical modelling 10. Summary

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To increase awareness and understanding of the phenomena

To provide guidelines for assets with existing flexible risers To provide guidelines for operators looking to use flexible

risers To develop a generic acoustic block To assess possible remedial modifications to existing risers To provide the industry with the information necessary to

redesign riser carcasses such that the phenomena no longer occurs

JIP Phase 1 - Objectives 1.

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Activity no.: 1 Description: Production for issue of a general awareness document

Objectives: Issue a general awareness document based on experience to date of the phenomenon, to help operators determine whether they have the flow induced pulsation problem, and if so, what immediate mitigation measures can be employed.

Activities: Using knowledge gained from recent investigation work, develop a general awareness document, e.g. what are the risks, what immediate measures can be taken, if you have the problem who to contact etc Produce an article for publication on: (i)the HSE website - Offshore Research Focus (ii)UKOOA Bob Kyle (BV to contact)

Deliverables: A short, concise document describing the phenomenon, what the risks are, what to do about it, and what expertise you need to source.

JIP Phase 1 CTRs 2.

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Activity (CTR) Sheet Activity no.: 2 Description: Assessment of Topsides and subsea measurement

data

Objectives: To issue guidelines on what processing techniques and assessment criteria should be used to analyse data recorded on subsea and topsides pipework.

Activities: Using knowledge gained from recent investigation work, summarise measurement and analytical techniques for both subsea and topside pipework. Clearly specify what to measure, where to measure it, effect of transducers on measurement, what data processing should be carried out etc Discuss with BP Aberdeen any progress they have made with regard to subsea pipework measurement (hardware) systems. Include an assessment of current subsea measurement system, i.e. potential issues such real-time measurements, stress measurements, cable-less data transmission.

Deliverables: A concise report describing current and potential future measurements, their analysis and assessment criteria.

2. JIP Phase 1 CTRs

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Activity (CTR) Sheet Activity no.: 3 Description: Riser vortex shedding theory development

Objectives: Generate a comprehensive understanding of the flow induced pulsation excitation mechanism, for a range of representative riser internal geometries, and the effect of process parameters and pipework configuration.

Activities: 1. Flow visualisation 2. Combined simulation and scale testing, to identify and characterise the source strength and pulsation, (evaluate the Howe Integral and Strouhal number), as a function of riser geometry and gas process properties. 3. Carry out an analytical assessment of aero-elastic interaction. 4. Extend analytical modelling to riser systems where there has not been a problem. 5. Compare scale models results with data measured on offshore installations. 6. Scale testing using 4 and/or 6 riser carcass sections; at ambient and higher pressures; using different riser profiles/suppliers; using air and natural gas; evaluate properties of carcass sections, e.g. damping; include any ideas from brainstorming meeting (CTR 5); evaluate effect of line pressure is it gas specific?. 7. Analytical assessment of acoustic pulsation interaction with the topsides and subsea pipework, e.g. the effect of source strength on whether lock-on occurs, and the effect of the topside pipework length (connected to riser).

A series of technical reports detailing the work undertaken, results, sources of data, any key assumptions, conclusions and recommendations: (i) flow visualisation tests; (ii) scale test and analytical model results for standard 4 and 6 riser carcass sections; (iii) aero-elastic interaction; (iv) comparison of scale testing with offshore results; (v) Final document to give guidelines as to when you are likely to have the problem, e.g. flowrates, riser geometry, gas dryness, riser length, gas pressures etc.

2. JIP Phase 1 CTRs

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Activity (CTR) Sheet Activity no.:4 Description: Full scale testing data analysis

Objectives: Identify common trends from actual recorded data

Activities: Carry out detailed analysis of data recorded on Schiehallion and Asgard (and other examples?), to identify common trends, for comparison with theory development and scale testing results etc. Develop a list of critical parameters

Deliverables: A concise written technical report describing: the work undertaken, results and comparison with CTR 3 results conclusions. Quantitative results will be provided in graphical format, wherever appropriate.

2. JIP Phase 1 CTRs

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Activity (CTR) Sheet Activity no.: 5 Description: Remedial riser modifications

Objectives: Identify possible riser modifications to reduce the level of flow induced pressure pulsation.

Activities: Brainstorming meeting to include a mixture of practical and theoretical experts from outside the JIP, experts within BP, Statoil and Exxon, and suitable representatives from the flexible riser manufacturers. BV to generate E-mail describing problem, to be sent out to potential experts for comment/review. Participants to then propose experts for involvement in meeting. Meeting to happen at second steering committee meeting (before scale testing is complete).

Deliverables: A short document listing potential options, and detailing those considered investigating further.

2. JIP Phase 1 CTRs

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Production of a general awareness document

Awareness document 3.

on public side of website widely distributed referred to in issued questionnaires requirement to re-issue at project end?

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4. Aero-elastic interaction

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Conclusions Structural modes (Ovaling and Longitudinal) of the riser

carcass do exist in the frequency range observed in offshore testing

It is considered unlikely that aero-elastic interaction is part of the primary excitation mechanism, but may play a part in mode selection

4. Aero-elastic interaction

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Information Information on 22 Risers

Flow information for 19 Full flow and riser details for 12 risers, such that detailed

analysis can be undertaken.

Comments There are no clear trends based on riser gas velocity,

corrugation gap width or depth as to why one riser resonates and not another

Questionnaire analysis 5.

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Offshore measurements 6.

Offshore data has been acquired for six flexible risers Typical survey included:

Topside and subsea vibration Topside dynamic stress at critical

locations Topside dynamic pressure (where

achievable)

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Offshore measurements 6

Riser A Response vs Flow

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Offshore measurements 6.

Example Frequency vs Velocity

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Acoustic simulation 7.

Analytical assessment of acoustic pulsation Topsides Subsea

To try and identify possible pipework sections with acoustic natural frequencies that match the pressure pulsation frequencies

Results show good match between both topsides and subsea

natural frequencies, and frequencies of concern Often simultaneously! Also predicts modes which dont occur

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1. Increased general awareness of the problem 2. The source of the pressure pulsations is vortex shedding from the corrugations of the carcass. 3. Identified that topsides and subsea piping acoustics are the principal feedback mechanism. 4. In some cases, aero-elastic interaction possibly contributes to the phenomenon. 5. At least 8 facilities worldwide are, or have been, subject to the problem: also more may experience the problem in the future. 6. Have agreement from outside experts on the excitation and response mechanisms.

JIP Phase 1 summary 10.

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7. Able to reproduce effect in scale tests, in air at atmospheric conditions, using machined profiles. 8. Starting to establish effect of carcass profile design, i.e. which parameters are the most important in the vortex shedding mechanism. 9. Numerical modelling has been able to predict parametric trends observed in scale testing. 10. Understand that Boundary layer thickness is significant this is dependent on pressure and gas composition.

JIP Phase 1 summary 10.