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Andy Saunders Tack - The Quest Integrity Group - Vibration management around vendor packages

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Andy Saunders Tack delivered the presentation at 2014 Gas Compressor Stations Conference. …

Andy Saunders Tack delivered the presentation at 2014 Gas Compressor Stations Conference.

The Gas Compressor Stations Conference is the only conference specifically dedicated to the design, build and maintenance of gas compressor stations.

For more information about the event, please visit: http://www.informa.com.au/gascompressors14

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  • 1. Vibration Induced Failure Avoidance and Management Around Vendor Packages Brisbane April 2014
  • 2. Why The Concern? • FIV (flow induced vibration) failures have lead to fatalities, fires and lost production – many of these around vendor packages • Vibration related failures in 2000 – 2010 represented on average deferment costs of A$1.5M per incident • Vibration typically not addressed comprehensively during project phase
  • 3. Vibration Mechanisms • Steady State – Flow induced turbulence (FIT): – Mechanical excitation – High frequency acoustic excitation (HFAE): – Pulsation • reciprocating machinery or rotating stall • flow induced excitation – Cavitation and Flashing • Transient Issues – Fast acting valves
  • 4. Vibration Mechanisms
  • 5. Assessment Process – Energy Inst. Guidelines • Approach relevant to all stages of project life. • Should be addressed at FEED • Particularly important for process or plant changes (MoC)
  • 6. Assessment Approach (Energy Inst. Guidelines) • Identify main lines and key process conditions • Identify rotating and reciprocating pumps • Locate deadlegs • Locate RVs
  • 7. FIV Screening - Technical Approach
  • 8. Main Pipework Assessment 34 Lines 3 Lines Typical Outcome for LNG Train
  • 9. Screening Survey Outputs
  • 10. Small Bore Connection Assessment
  • 11. Small Bore Connection Bracing
  • 12. Examples of Good and the Less Good
  • 13. Case Study 1: Compressor Pipework Background: • Project to increase throughput as consequence of new “tie-in” • Increased duty planned for compressor • Increased plant capacity >100% of design Objective to understand integrity impact
  • 14. Suction Line Discharge Line Recycle Line Dead Leg A Dead Leg B Actual Configuration
  • 15. Flow Flow Vortices Side Branch d L 0 20 40 60 80 100 120 140 0 50000 100000 150000 200000 250000 300000 350000 400000 450000 500000 Flow Rate (kg/hr) NaturalFrequency(Hz) f5/4 f3/4 f1/4 Quarter Wave Acoustic Frequencies Vortex Shedding Frequencies 1,3 2,1 1,1 Quarter Wave Acoustic Frequencies Vortex Shedding Frequencies Solution: modified location of valve Analysis of Deadlegs
  • 16. Case Study 2: RV Piping Valves closed – no flow Flow Valve closed – no flow Main Pipe OD is 48” Situation: New flare tie-ins as part of plant expansion
  • 17. Design Marginal Correction Danger Perception Level 0.01 0.1 1 10 1 10 100 1000 Frequency (Hz) VibrationalAmplitude(mm)-PeaktoPeak Wachel and Bates Criteria Vibration of Flare Take-offs Observed
  • 18. Detailed Analysis: Vortex Shedding Frequency • Spectral densities of flow kinetic energy and pressure traces at the RV take-off mouths’ are used to estimate dominant vortex shedding frequencies at each mouth. Examples are shown below. Dominant shedding frequency is 10.5 Hz for this 18 inch take-off Flow
  • 19. Root Cause of Vibration Field data and analysis indicate that the root cause of vibrations is due to “lock-in” of RV take-off mouth vortex shedding frequency and RV take-off piping (standing wave) acoustic resonant frequency. • Piping vibration frequencies (measured): 6.25 Hz, 12.5 Hz • RV piping first acoustic resonant frequency range (computed): 6.0 Hz – 10.5 Hz • RV take-off mouth vortex shedding frequency range (computed): 6.0 Hz – 30.0 Hz
  • 20. Vortex Shedding Frequency • Closely spaced 18 inch take-offs show high energy content at a frequency of 6.4 Hz • Shedding frequency can easily “lock-in” to a first acoustic resonant frequency (e.g. f1 ~ 6.0 Hz) , at which point pulsations and energy content will start to amplify. Flow
  • 21. Analysis Summary • Vortex shedding frequencies and first acoustic natural frequencies of RV piping are too close! • Based on flow & acoustic analyses a response curve (for the 18 inch take-offs) which predicts the onset of pulsations can be constructed: First acoustic resonance frequency range of 18 inch RV piping Principal shedding Strouhal curves (blue, red, green), are identified from CFD analysis. First mode (red) is associated with highest pulsation amplification potential. Onset of significant pulsation happens when flow ~ 8 m/s (slightly above 10,000 tons /day). True onset of pulsation occurs at ~ 5 m/s, but is most likely very weak (blue curve is a high mode of shedding) “Lock-out” may occur for flow > 18 m/s. Not practical solution to avoid pulsations.
  • 22. Vibration Mitigation Solutions • Move the relief valves closer to the take-off points. This will have the effect of increasing the acoustic resonant frequencies of the RV piping. • Modify the RV take-off mouths to minimize / weaken vortex shedding. Example: Forge entrance pieces to provide a 45-deg funnel into the RV piping. Minimize flow-tripping weld protrusions when welding the piece in place. Some simulation work is recommended to ensure that a design would work. • Install orifice plates just upstream of the take-off points. The plates will suppress vortex shedding and increase the acoustic resonant frequencies of the RV piping. The plates would have to be carefully designed to retain original relief capacity. Vibration mitigation is achieved by de-tuning the vortex shedding frequency and the RV piping first acoustic resonant frequency. Candidate action items are:
  • 23. Detailed Analysis – Potential Approaches
  • 24. Conclusions • Address vibration Issues holistically at the plant level and ensure provision is in place for projects – Energy Inst. Guidelines • Ensure vibration management process is in place for new and existing assets to allow impact of plant or process changes on integrity to be quantified • Ensure vibration management processes are in place around “grey area” equipment where responsibilities are potentially not well defined or coordinated • Ensure flow induced vibration is considered as part of MoC process. • Ensure awareness of FIV issues amongst integrity stakeholders