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Experience that DeliversExperience that Delivers
Slug Induced Vibrations in Pipeline and Jumper Spans –Enhanced industry design and analysis methods enabled by the SLARP JIP
Slugfest
Kieran Kavanagh – Technology & Engineering Director, Wood Group Kenny
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Introduction
1. Problem Definition2. Load-Response Model3. Load Contributions4. Techniques & Tools for Slug Modeling5. Numerical Example 6. SLARP JIP & Its Significance7. Future Developments
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Problem Definition
• Cause of Slugs in Subsea Structures‐ Variation in Flow in Flowlines, Risers, Jumpers
• Why is slug‐flow a issue?‐ Time‐varying fluid forces‐ Leads to:
i. Vibrationii. Reduced fatigue marginsiii. Higher utilizations
‐ In severe cases, slugging can lead to equipment change‐out
• Problems with Slugging Analysis‐ Complex loading regime – Difficult to represent efficiently‐ Coupling of all slug loading load terms‐ State of practice not consistent across industry
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1. Mechanics of combining various slug load contributors2. Worked example for a generic subsea spool configuration,
susceptible to slug responseand key parameter sensitivities
3. Comparison of responses from different Software Tools4. Outline of Scope of SLARP JIP
• modelling & analysis of sample field systems.• industry guidelines• full scale validation testing • Relevance to industry understanding of problem
Slide 4
Focus of Presentation
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Techniques Available for Slug Modelling & Analysis
• Many available and under developed:‐ Proprietary Riser‐Flowline Vs General Purpose Analytical Tools‐ Slug Unit (idealised) Vs Stochastic Slug History‐ Structural Considerations Vs CFD Considerations‐ Forcing Functions VsMoving Mass Methods
• What do you choose?‐ Depends on specifics of particular problem at hand and system
component under consideration
Slide 5
- Normal and Tangential Loads- Driven by Mass Variation Across Structural Elements
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• Idealised Slug Unit approach to modelling principal components of slug flow‐ Typical for analysis of rigid spools‐ Slug profiles predicted & binned
with defined ranges‐ Equivalent densities of fixed lengths
selected‐ Unit velocity assumed constant
• Alternative approaches that consider stochastic slug data can be more applicable to long pipelines and free‐spans
Slide 6
IDEALISED SLUG UNIT REPRESENTATION
Analytical Representation
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Four principal slug load contributors:1. Gravitational and inertia effects 2. Forces on Bends (centrifugal force)3. Axial tension effects / dynamic pressure4. Coriolis effects
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SLUG load contributors
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Slide 8
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Fg = mgFi = mx’’
FM = mi vi2 K FM
Gravitational and Inertia Effects
Forces on Bends
SLUG load contributors 1 & 2
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Slide 9
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Tw= mi vi2
FCo= -2mi vi es
Axial Tension and Dynamic Pressure Effects
Coriolis Effects
SLUG load contributors 3 & 4
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Dynamic Amplification
• Bend Entry and Exit Effects – Dynamic amplification of response• Stress amplification
‐ Can be 1.0 to 2.0 (Restrained piping , moderate stiffness) ‐ Greater than 2.0 (Compliant systems)
Slide 10
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Numerical ExampleModel general arrangement
• Compliant rigid spool• Partial seabed support• Buoyancy support• Smooth mass and load transition method
• Flexcom Slug Module analysis (base case)
• Independent Abaqus comparisons performed
Slide 11
10” OD 15mm wt
NOTE: FOCUS LOCATIONS (BENDS) FOR THIS PAPER ARE CIRCLED IN RED
Animations
200m SlugSingle 1m/s
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Vertical ReactionsLow Velocity Case
Slide 13
Animations
200m SlugSingle 1m/s
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Vertical Displacement (Point B)Low Velocity Case
Slide 14
Animations
200m SlugSingle 1m/s
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Bending Moment (Point B)Low Velocity Case
Slide 15
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Slide 16
Bending Moment (Point E)Low Velocity Case
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Vertical Reactions (FTA)Higher Velocity Case
Slide 17
Animations
200m SlugSingle 5 m/s
50m SlugSingle 5 m/s
200m SlugMulti 5m/s
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Vertical Reactions (LRA)Higher Velocity Case
Slide 18
200m SlugSingle 5 m/s
Animations
50m SlugSingle 5 m/s
200m SlugMulti 5m/s
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Vertical Displacement (Point E)Higher Velocity Case
Slide 19
Animations
200m SlugMulti 5m/s
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Local Bending Moment (Point B)Higher Velocity Case
Slide 20
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Local Bending Moment (Point E)Higher Velocity Case
Slide 21
200m SlugMulti 5m/s
Animations
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Bending Moment (Point A)Higher Velocity Case
Slide 22
NOTE: POINTS B & CRESTRAINED
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Influence of Density and Velocity Variation
Slide 23
Animations
50m SlugSingle 5 m/s
200m SlugSingle 10 m/s
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Slug Loading and Response in Pipelines SLARP JIP – Phase 1
• Objectives– Best practice for design analysis of pipelines, jumpers and risers
subject to slug loading.• Membership
• JIP Scope State of Practice – Technology Gap Evaluation Loading (Slug Flow) Characterisation Response (Structural Deformation) Characterisation Worked Examples Slug Loading & Response Guidelines Phase II - Testing & Calibration Program Plan
• Project Funding JIP Funding $616,500 (from 9 members)
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Conclusions• We now have good confidence in the input‐response modelling of slugs, provided the input (and its time dependence) is known
• Enhanced Time domain analysis of slugging requires Robust mechanics of combining various slug load contributors Validation of method with different analytical tools
• In general, good agreement is observed between analysis tools variation due to included load terms, mass smoothing, seabed model ∆ρv2 a key response driver for compliant structures Significant complexity in modelling with general purpose tool (Abaqus)
• Amplification of response due to periodic forces (harmonic slug loading) is possible in both simple or complex 3D shapes
• Key uncertainties remain around defining the slug loading environment (over life and locally)
• Role of CFD is evolving as a contributor to solving the problem
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Capability Enhancements and Further Planned Testing
• Improved modelling capabilities (Flexcom): Accelerating Slugs (user‐defined velocity as function of
time for each slug head and tail) Variability in slug (vs. pocket) length over time Varying density along slug length (user‐defined density
profile as function of time for each slug head and tail)• Additional validation (SLARP JIP Testing) Multiple slugs (slug train) testing Testing at larger diameter Multi‐planar configuration testing
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Animation
ObjectivesBest practice for design analysis of pipelines, jumpers and risers subject to slug loading.
Membership (Phase 2)
Scope (Phase 2) Slug Flow Testing Programme Test Data Analysis and Validation of Numerical Models Update of Slug Loading and Response on Pipelines (SLARP) Guidelines Phase 3 Front End Study
Test Program (Phase 2)Physical testing at Southwest Research Corporation – horizontal-U test piece
Project Funding (Phase 2) Current Funding $980k with 8 members – additional work planned
Proposed Scope (Phase 3) Additional physical testing & validation Scope being confirmed (larger diameter, configurations, slug trains)
Slug Loading and Response in Pipelines SLARP JIP Phases 2 & 3
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Acknowledgements
Adrian Connaire, Wood Group Kenny, GalwayJason Payne, Wood Group Kenny, GalwayJonathan McLoughlin, Wood Group Kenny, GalwayAengus Connolly, Wood Group Kenny, GalwayChristian Chauvet, Wood Group Kenny, Aberdeen
