Slug Induced Vibrations in Pipeline and Jumper Spans Enhanced industry design and analysis methods enabled by the SLARP JIP

Transcription

1 Slugfest Slug Induced Vibrations in Pipeline and Jumper Spans Enhanced industry design and analysis methods enabled by the SLARP JIP Kieran Kavanagh Technology & Engineering Director, Wood Group Kenny Experience that Delivers Experience that Delivers

2 Introduction 1. Problem Definition 2. Load-Response Model 3. Load Contributions 4. Techniques & Tools for Slug Modeling 5. Numerical Example 6. SLARP JIP & Its Significance 7. Future Developments 1

3 Problem Definition Slide 2 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. Vibration ii. Reduced fatigue margins iii. 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 2

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5 Slide 4 Focus of Presentation 1. Mechanics of combining various slug load contributors 2. Worked example for a generic subsea spool configuration, susceptible to slug response and key parameter sensitivities 3. Comparison of responses from different Software Tools 4. Outline of Scope of SLARP JIP modelling & analysis of sample field systems. industry guidelines full scale validation testing Relevance to industry understanding of problem 4

6 Techniques Available for Slug Modelling & Analysis Slide 5 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 Vs Moving Mass Methods What do you choose? Depends on specifics of particular problem at hand and system component under consideration - Normal and Tangential Loads - Driven by Mass Variation Across Structural Elements 5

7 Slide 6 Analytical Representation 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 IDEALISED SLUG UNIT REPRESENTATION Alternative approaches that consider stochastic slug data can be more applicable to long pipelines and freespans 6

8 Slide 7 SLUG load contributors Four principal slug load contributors: 1. Gravitational and inertia effects 2. Forces on Bends (centrifugal force) 3. Axial tension effects / dynamic pressure 4. Coriolis effects 7

9 Slide 8 SLUG load contributors 1 & 2 1 Gravitational and Inertia Effects F g = mg F i = mx 2 Forces on Bends F M = m i v i2 K F M 8

10 Slide 9 SLUG load contributors 3 & 4 3 Axial Tension and Dynamic Pressure Effects T w = m i v i 2 4 Coriolis Effects F Co = -2m i v i e s 9

11 Slide 10 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) 10

12 Numerical Example Model general arrangement Slide 11 Compliant rigid spool Partial seabed support Buoyancy support Smooth mass and load transition method Flexcom Slug Module analysis (base case) Independent Abaqus comparisons performed 10 OD 15mm wt NOTE: FOCUS LOCATIONS (BENDS) FOR THIS PAPER ARE CIRCLED IN RED Animations 200m Slug Single 1m/s 11

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14 Vertical Reactions Low Velocity Case Slide 13 Animations 200m Slug Single 1m/s 13

15 Vertical Displacement (Point B) Low Velocity Case Slide 14 Animations 200m Slug Single 1m/s 14

16 Bending Moment (Point B) Low Velocity Case Slide 15 15

17 Bending Moment (Point E) Low Velocity Case Slide 16 16

18 Vertical Reactions (FTA) Higher Velocity Case Slide 17 Animations 200m Slug Single 5 m/s 200m Slug Multi 5m/s 50m Slug Single 5 m/s 17

19 Vertical Reactions (LRA) Higher Velocity Case Slide 18 Animations 200m Slug Single 5 m/s 200m Slug Multi 5m/s 50m Slug Single 5 m/s 18

20 Vertical Displacement (Point E) Higher Velocity Case Slide 19 Animations 200m Slug Multi 5m/s 19

21 Local Bending Moment (Point B) Higher Velocity Case Slide 20 20

22 Local Bending Moment (Point E) Higher Velocity Case Slide 21 Animations 200m Slug Multi 5m/s 21

23 Bending Moment (Point A) Higher Velocity Case Slide 22 NOTE: POINTS B & C RESTRAINED 22

24 Influence of Density and Velocity Variation Slide 23 Animations 50m Slug Single 5 m/s 200m Slug Single 10 m/s 23

25 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) 24

26 Slide 25 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 25 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 ρv 2 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

27 Slide 26 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 26

28 Slug Loading and Response in Pipelines SLARP JIP Phases 2 & 3 Objectives Best practice for design analysis of pipelines, jumpers and risers subject to slug loading. Membership (Phase 2) Scope(Phase2) 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 Animation 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) 27

29 Acknowledgements Adrian Connaire, Wood Group Kenny, Galway Jason Payne, Wood Group Kenny, Galway Jonathan McLoughlin, Wood Group Kenny, Galway Aengus Connolly, Wood Group Kenny, Galway Christian Chauvet, Wood Group Kenny, Aberdeen 28

30 Thank You Any Questions 29