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

29 Photos courtesy of MSI

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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