Transient Analysis and Design Considerations for Hydraulic Pipelines. Jonathan Funk, EIT

Transcription

1 Transient Analysis and Design Considerations for Hydraulic Pipelines Jonathan Funk, EIT

2 Transient Analysis 2 Objectives Develop an intuitive understanding of water hammer and transient response Present a case study where transient analysis mattered NOT Teach the science of wave formation and propagation (too many formulas)

3 Transient Analysis 3 Definitions Water Hammer (noun) The concussion and accompanying noise that result when a volume of water moving in a pipe suddenly stops or loses momentum. Transient Response (noun) The response of a system to a change from equilibrium. Source: water hammer. (n.d.). Dictionary.com Unabridged. Retrieved May 19, 2015, from Dictionary.com website: hammer

4 Transient Response 4 Everyone s Favorite Analogy Flow > Energy Absorption

5 Transient Analysis 5 Overview So Far Decelerating flow increases pressure Pressure spikes can travel and oscillate throughout a pipeline Design for transient pressures! (not just Steady State ) Prevent or absorb pressure spikes

6 Transient Analysis Case Study Skookum Creek Power Project 6

7 7

8 8 March 11, 2011

9 Skookum Creek Power Project 9 Located near Squamish, BC 6.4 km FRP & Steel pipeline m diameter 340m elevation change 9,900 L/s design flow Rated Capacity: ~25 MW March 11, 2011

10 Skookum Creek Power Project 10 Hydraulic Scenarios Power Generation = Flow x Pressure = $ (Steady State) Normal shut-down No long-term damage (Transient) Emergency shut-down No short-term damage (Transient) Needle Valve Failure Survivability (Transient)

11 Transient Analysis 11 Pressure Rise Reservoir Max HGL Envelope Hydraulic Grade Line (Steady State) P P Flow > P Min HGL Envelope Gate valve where P = change in head (m) (pressure rise) (negative pressure) a = wave speed (m/s) ( communication speed) g = acceleration of gravity (m/s 2 ) V = change in velocity (m/s)

12 Transient Analysis 12 Negative Pressure & Cavitation Siphon -14 psi At standard temperature and pressures, cavitation starts at -10m HGL (-14 psi)

13 Skookum Creek Power Project 13 Design Limitations Topography Hydrology & Wetlands Old Growth Management Areas (protected) Site Access (de-activated forest service roads) Geotechnical Conditions Max/Min Elevations Hydraulics!

14 Skookum Creek Power Project 14 Steady State Analysis More headloss = less pressure = less power generation Design flow and pipeline deterioration Siphon! Hard to release air. Closer to Cavitation. Remote site considerations Recommendation: Eliminate Siphon

15 Normal Operations (12 minute shut-down) 15 Outcomes Nothing to worry about Ongoing, successful operation

16 Emergency Shut-down 16 Max Transient HGL Min Transient HGL Negative Pressure Surge Tower Initial Outcomes Negative Pressures (enough for cavitation) Initial Emergency Period too short Additional protection required Recommendation: Add a Surge Tower

17 Emergency Shut-down (90 seconds) 17 Surge Tower Final Outcomes Determined 90 second threshold for emergency shut-down Addition of surge tower (doubles as air release) Successfully completed project, potential problems prevented

18 Transient Analysis 18 Overview P V ( is proportional to ) Design for pressure spikes (not just steady state) -14 psi = Cavitation (please avoid) Change flows as slow as you can manage Transient Analysis is understanding and mitigating these phenomenon

19 Transient Analysis 19 Common Sources of Water Hammer Valve Operation (Fast AND Slow) Pump Start-up / Pump Shut-down Power Failure Mitigation Perform a transient analysis Slow down your flow changes (prevention!) Pressure relief / vacuum break Combination air release / vacuum valves Surge tanks

20 Special thanks to: Adrian Gygax (Gygax Engineering Associates) Peter Zell (Run of River Power) Ted Steele (KWL) Steve Mills (KWL) Transient Analysis and Design Considerations for Hydraulic Pipelines Jonathan Funk, EIT