Related Considerations and How Much is Too Much? · PDF filePump Vibration Related...
Transcript of Related Considerations and How Much is Too Much? · PDF filePump Vibration Related...
October 12, 2017
Pump Vibration Related Considerations and
How Much is Too Much?MWEA Collection Systems Seminar
Steve Fehniger, P.E.
Agenda
Presentation Focus Areas
Pump Vibration Considerations• Operating region review
• Why do pumps vibrate more than acceptable levels?
Pump Vibration Standards (How much is too much?)
Vibration Testing
Dynamic Vibration Analyses
Case Study: Marter Road Booster PS
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Presentation Focus Areas
Centrifugal (subset of rotodynamic) pumps• Excludes positive displacement pumps
Wastewater and combined sewage pumping applications • Solids handling pumps (non-clog)
Constant and variable speed
New and existing pumping systems
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Pump Vibration Considerations
Pumps are rotating machinery
Pumps will vibrate if operating – to certain level, acceptable and expected
Challenges:
• Minimize vibration to extent feasible
• Understanding if a pump is vibrating too much
• Do not want to take good equipment out of service or create acceptance limits that are overly constraining
• Understanding why a pump is vibrating
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Pump Operating Regions
Defined in ANSI/HI 9.6.3
Preferred operating region (POR) • Includes BEP
Allowable operating region (AOR)• Beyond POR
KEY: As move away from POR pump vibration increases
Where is your pump operating? How “happy” is it?
If change operating conditions will pump be happier?
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POR & AOR for Pump in Dynamic Headloss Dominated System
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POR & AOR for Pump in Static Head Dominated System
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Why do pumps vibrate?
What operating region?
Inadequate pump support &/or pipe support
Poor installation – level, uniform support, adequate anchorage
Pump internal issues – misalignment, imbalance, bent shaft, etc.
Poor intake conditions
Resonance• Need to avoid
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Inadequate Pump Support/Installation
Major contributor to pump vibration
Steel frames provided by many manufacturers lack adequate stiffness
Addition of steel cross members effective for vibration control, but limits access
Installation of support base is critical to minimizing vibration –leveling, proper grouting, securing anchor bolts, etc.
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Inadequate Pipe Support = Nozzle Loading
Flexible Couplings & Pipe Supports
Reduce rigidity of system
Support pipe
HI requires that loads on suction and discharge nozzle be minimized
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ResonanceWhat is a “Critical Speed”?
Where a system natural frequency can become resonant if various excitation sources are in close proximity to natural frequency. Excitation sources include:pump speed, 2x pump speed, vane-pass frequency, etc.• Variable speed systems
are especially vulnerable to this problem
• Often system is modified to move natural frequency out of operating range
• Can also speed limit or exclude speeds
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Resonance: Vibration and Critical Speed Limitations – Tools to Predict
Finite Element Analysis• What is a Finite Element Analysis (FEA)?
Computer model of mechanical equipment to predict natural frequencies of equipment or structure behavior when excited
• FEA should normally be performed for pumps greater than 100HP and for critical pump applications
• FEA should only be performed by qualified firms
• Investment in FEA is a proactive approach similar in philosophy to Physical Intake Model
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HI Pump Vibration Standards
Standards and guidelines for how much is too much?
Standards available
• ANSI/HI 9.6.4 ‐ Rotodynamic pumps – vibration measurements and allowable values
• ANSI/HI 9.6.5‐ Rotodynamic pumps – guideline for condition monitoring
• ANSI/HI 9.6.8 ‐ Rotodyamic pumps – guideline for dynamics of pumping machinery
‐ Provides background theory on analysis methods for vibration and recommendations for levels of analysis from simple to complex
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Pump Vibration Standards –How much is too much?
HI Pump Vibration Standard (ANSI/HI 9.6.4-2016)
Depicts maximum allowable vibration levels for different pump designs (new installation)
Specifies how field and factory vibration tests are to be performed
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Image courtesy of the Hydraulic Institute www.pump.org
Pump Vibration Standards –How much is too much?
Pump Condition Monitoring (ANSI/HI 9.6.5-2016)
Recommended vibration velocity limits for alarm and shutdown
Alert: 130% of baseline measurement
Alarm: 150% of field acceptance level
Shutdown: 200% of field acceptance level
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Image courtesy of the Hydraulic Institute www.pump.org
Vibration Testing
Key drivers for testing:• Acceptance of new pumps
• Condition assessment of existing pumps
• Historical monitoring to allow identification of change (written records or historian)
• Determine natural frequencies of system
Major instruments• Laptop with data acquisition software
• Data analyzer with sufficient channel count
• Tri-axial and uni-axial accelerometers
• Instrumented impact hammer
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Photo courtesy of Mechanical Solutions, Inc. (MSI)
Tri-axial accelerometer
9.6.4 Guidance –Where to Measure Vibration
17 Courtesy of the Hydraulic Institute, pumps.org
Image curtesy of the Hydraulic Institute www.pump.org
Vibration Testing –ANSI/HI 9.6.4 Acceptance Criteria
For pump type groupings provides overall vibration velocity acceptance criteria (ips RMS)
For solids handling pumps acceptable values dependent on:• Pump power (BHP)
• Vertical vs. horizontal orientation
• Operating region (POR or AOR)
For operation below 600 rpm add allowable displacement (mils)• Factory vs. field
• AOR vs. POR
• Adder for height above foundation
• Adder for solids handling
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Dynamic Vibration Analysis
What?
• Methods to calculate/model pump system to determine if will be a problem – various levels of analysis
When applied?
• Guide to equipment selection and system configuration
• Evaluation of system when problems identified or failure occurs
Conversion from constant speed to VFD speed control
• Caution: much broader range of operating frequencies (speeds)
ANSI/HI 9.6.8 provides system risk evaluation method and guidance on analyses required
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Example of Failure Due to Resonance
Vertical turbine in resonance due to 1x full speed rpm excitation
Shaft fatigue failure and weld cracking just below foundation
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Broken 5.5-in diameter shaft
Photo courtesy of MSI
Example of Failure Due to Resonance
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Column gusset weld failure close-up
Discharge head and top of column
Post-installation FEA Analysis output (ODS)
Photos and graphic courtesy of MSI
Case Study: Marter Road Booster PS (MRBPS)
Owner/operator: Wayne County
Location: St. Clair Shores, MI
Function: Booster to combined sewage during high flow conditions
Project goals: Rehabilitation of pump, increase capacity and added speed control to cover range of conditions
• Include considerations to avoid resonant condition
Pump type/No.: Three vertically mounted end-suction
Manufacturer: 30-in Fairbanks Morse model 5710 angle-flow New rated point: 22,890 gpm (33 mgd) at 20.5 ft TH
Flow rate range: 22,890 – 6,300 gpm (51 to 14 cfs)
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MRBPS – Lower Level Plan
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MRBPS - Section
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MRBPS –Vibration Testing and Dynamic Analysis
Vibration testing of existing pump system to establish natural frequencies
Dynamic vibration analysis (FEA) utilized to guide shafting and motor criteria to minimize potential for resonance
Validation dynamic analysis for selected equipment –confirmed acceptable
Post-installation validation testing – acceptable vibration levels and demonstrate not in resonance
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MRBPS –Location of Tri-axial Accelerometer Vibration Sensors for Existing Pump System
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Motor
Vertical
Parallel
Perpendicular
Vertical
Parallel
Perpendicular
Intermediate bearing and drive shaft
Vertical
Parallel
Perpendicular
Pump
Vertical
Perpendicular
VerticalParallel
Perpendicular
Parallel
3D views courtesy of Mechanical Solutions, Inc. (MSI)
MRBPS –Existing Pump System Equipment
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Vertically mounted solids handling pump
Pump support base
MRBPS –Existing Pump System Equipment (cont.)
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Extended shafting Original 125 HP motors
MRBPS –Vibration Testing
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Laptop and data analyzer Pump instrumented with shaft proximity probes and accelerometers
MRBPS –Vibration Testing (cont.)
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Accelerometer on bearing frame
Accelerometers to determine structure vibration characteristics
Photos courtesy of MSI
MRBPS –Pump System After Improvements
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Rehabilitated pumps and extended shafting
Rehabilitated pump
MRBPS –Pump System After Improvements (Cont.)
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New 150 HP motors and motor bases
MRBPS –Pump System After Improvements (Cont.)
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Motor instrumented with vibration sensors
Acknowledgements
Hydraulic Institute (HI)
Mechanical Solutions, Inc. (MSI)
Wayne County Department of Environment
Julie Aichler, CDM Smith
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