Pump Vibration. Related Considerations and How Much is Too Much? MWEA Collection Systems Seminar. Steve Fehniger, P.E.

Transcription

1 Pump Vibration Related Considerations and How Much is Too Much? MWEA Collection Systems Seminar Steve Fehniger, P.E. October 12, 2017

2 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 2

3 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 3

4 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 4

5 Pump Operating Regions Defined in ANSI/HI 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? 5

6 6 POR & AOR for Pump in Dynamic Headloss Dominated System

7 7 POR & AOR for Pump in Static Head Dominated System

8 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 8

9 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. 9

10 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 10

11 Resonance What 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 11

12 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 12

13 HI Pump Vibration Standards Standards and guidelines for how much is too much? Standards available ANSI/HI Rotodynamic pumps vibration measurements and allowable values ANSI/HI Rotodynamic pumps guideline for condition monitoring ANSI/HI 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 13

14 Pump Vibration Standards How much is too much? HI Pump Vibration Standard (ANSI/HI ) Depicts maximum allowable vibration levels for different pump designs (new installation) Specifies how field and factory vibration tests are to be performed Image courtesy of the Hydraulic Institute 14

15 Pump Vibration Standards How much is too much? Pump Condition Monitoring (ANSI/HI ) 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 Image courtesy of the Hydraulic Institute 15

16 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 Tri-axial accelerometer Major instruments Laptop with data acquisition software Data analyzer with sufficient channel count Tri-axial and uni-axial accelerometers Instrumented impact hammer Photo courtesy of Mechanical Solutions, Inc. (MSI) 16

17 9.6.4 Guidance Where to Measure Vibration Image curtesy of the Hydraulic Institute 17 Courtesy of the Hydraulic Institute, pumps.org

18 Vibration Testing ANSI/HI 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 18

19 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 provides system risk evaluation method and guidance on analyses required 19

20 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 Broken 5.5-in diameter shaft Photo courtesy of MSI 20

21 Example of Failure Due to Resonance Column gusset weld failure close-up Discharge head and top of column Post-installation FEA Analysis output (ODS) 21 Photos and graphic courtesy of MSI

22 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) 22

23 23 MRBPS Lower Level Plan

24 24 MRBPS - Section

25 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 25

26 MRBPS Location of Tri-axial Accelerometer Vibration Sensors for Existing Pump System Vertical Perpendicular Vertical Parallel Parallel Perpendicular Vertical Parallel Vertical Perpendicular Parallel Perpendicular Parallel Vertical Motor Perpendicular Intermediate bearing and drive shaft Pump 26 3D views courtesy of Mechanical Solutions, Inc. (MSI)

27 MRBPS Existing Pump System Equipment Pump support base 27 Vertically mounted solids handling pump

28 MRBPS Existing Pump System Equipment (cont.) Extended shafting Original 125 HP motors 28

29 MRBPS Vibration Testing Laptop and data analyzer Pump instrumented with shaft proximity probes and accelerometers 29 Photos courtesy of MSI

30 MRBPS Vibration Testing (cont.) Accelerometer on bearing frame Accelerometers to determine structure vibration characteristics 30 Photos courtesy of MSI

31 MRBPS Pump System After Improvements Rehabilitated pumps and extended shafting Rehabilitated pump 31

32 MRBPS Pump System After Improvements (Cont.) New 150 HP motors and motor bases 32

33 MRBPS Pump System After Improvements (Cont.) Motor instrumented with vibration sensors 33

34 Acknowledgements Hydraulic Institute (HI) Mechanical Solutions, Inc. (MSI) Wayne County Department of Environment Julie Aichler, CDM Smith 34

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