Back to Basics Rubbing or Not? Presented by: G. Richard Thomas, - - PowerPoint PPT Presentation

Presented by:

• G. Richard Thomas, P.E.

Principal Engineer SETPOINT™ Minden, NV USA

Back to Basics – Rubbing or Not?

Vibration Institute Piedmont Chapter

26 June 2015

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 2

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Historical Perspective

Machinery Diagnostics Data Acquisition System Circa April 1984

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 3

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Machinery Diagnostics Data Acquisition System Circa April 2015

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 4

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Introduction

It is not sufficient to only evaluate whether or not a rub is present. One must also make every effort to try and gain insight as to the initiating mechanism that has caused the rub to occur in the first place. A rub is not a machinery malfunction in and of itself. A rub always results from some other primary malfunction source such as:

 high vibration  tight or incorrect clearance  thermal growth  rotor bowing  distorted / twisted turbine casing or bearing housing

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 5

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Introduction

There are several symptoms that may be indicators that a rub is present:

• 1. Thermal bowing of the rotor
• 2. Abnormal changes in shaft centerline position
• 3. Changes in 1X vibration behavior at constant speed.
• 4. Abnormally high 1X vibration amplitude while trying to pass

through a critical speed

• 5. “Modified” critical speed frequency response region
• 6. Abnormal (elliptical or highly elliptical) orbit shape
• 7. Significant reverse precession vibration components
• 8. Sub and / or super harmonic vibration components
• 9. Wear, damage, loss of efficiency

10.Noise 11.Leaks

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 6

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Introduction

VIBRATION SIGNAL CHARACTERISTICS

• 1. Amplitude:

– Overall / Direct – nX Filtered

• 2. Phase
• 3. Frequency
• 4. Form / Shape (XYpair)
• 5. Radial / Axial Position
• 6. Precession

1.a Direct Amplitude

• 3. Frequency
• 2. Phase

1.b 1X or nX Amplitude

• 1. Yshaft
• 5. DC Gap volts

Ycasing

Once-per-turn event Phase Trigger

• 4. Shape

[Ref 23]

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 7

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Introduction

The first item to be realized is that radial or axial rubbing is not a machinery malfunction. A rub is secondary indicator that occurs when there is contact between rotating and non-rotating components. Some of the primary causes that can lead to a rub are:

 high vibration  tight or incorrect clearance  thermal growth  rotor bowing, etc.  distorted / twisted turbine casing or bearing housing

A rub can be radial, axial or a combination of the two. When the actual rub/stator contact occurs over a small fraction of the vibration cycle, it is called partial rub. When it occurs over a majority or all of the vibration cycle, maintaining continuous contact, it is called full annular rub. A partial rub is the most common manifestation.

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 8

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Introduction

• A rub will change the synchronous (1X) behavior of the rotor system

and will also change the dynamic stiffness in complex (non-linear) ways.

• Contact can also be either a “dry” rub or a “lubricated” rub.
• Typically, the point of contact for a dry rub, with dis-similar stator and

rotor materials, will wear rather quickly and the rub will “clear” itself is a short period of time.

• A lubricated rub can exhibit very slow wear and persist for an extended

period of time.

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 9

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Introduction

• During the period of contact, the tangential friction force appears

which is proportional to the magnitude of the radial force and the coefficient of friction at the sliding interface.

• The tangential friction force acts opposite to the surface velocity of the

shaft.

• It produces a torque on the rotor and, at the same time, tries to

accelerate the rotor centerline in the reverse precession direction.

• For this reason, a rub will produce reverse components in the full

spectrum.

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 10

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Introduction

• The frictional forces that are present during a rub produce local heating
• f the surface.
• If, at a steady operating speed, a rub occurs repeatedly in the same

place on the rotor, the frictional heating of the surface and associated thermal expansion in that area will cause the rotor to bow in the direction of the rub contact.

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 11

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Example #1: W501D5A Industrial Frame Gas Turbine / Generator

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 12

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Example #1: W501D5A Industrial Frame Gas Turbine / Generator

Bearing #2 105 MW Bearing #1 105 MW

9.47 mil pp / 5.62 mil pp 5.17 mil pp / 5.09 mil pp

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Example #1: W501D5A Industrial Frame Gas Turbine / Generator

13 mil pp 8.4 mil pp

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Example #1: W501D5A Industrial Frame Gas Turbine / Generator

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Example #1: W501D5A Industrial Frame Gas Turbine / Generator

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Example #2: Westinghouse 271 MW Steam Turbine / Generator

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 17

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Example #2: Westinghouse 271 MW Steam Turbine / Generator

• Dynamic Eccentricity Probe
• Measure of residual rotor bow due to gravity.
• Prior to startup, dynamic eccentricity must be below a maximum

allowable value.

• Although the eccentricity monitor typically becomes inactive above 600

rpm, the data from the eccentricity probe is always available via the monitor channel buffered output.

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 18

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Example #2: Westinghouse 271 MW Steam Turbine / Generator

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 19

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Example #2: Westinghouse 271 MW Steam Turbine / Generator

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 20

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Example #2: Westinghouse 271 MW Steam Turbine / Generator

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 21

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Example #2: Westinghouse 271 MW Steam Turbine / Generator

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 22

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Example #2: Westinghouse 271 MW Steam Turbine / Generator

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 23

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Example #3: General Electric 53 MW Steam Turbine Generator

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 24

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Example #3: General Electric 53 MW Steam Turbine Generator

Bearings #1 - #4 Unfiltered Shaft Relative Orbits 3380 rpm

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 25

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Example #3: General Electric 53 MW Steam Turbine Generator

Bearings #1 - #4 Unfiltered Shaft Relative Orbits 3530 rpm

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 26

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Example #3: General Electric 53 MW Steam Turbine Generator

Bearings #1 - #4 Unfiltered Shaft Relative Orbits 3565 rpm

4.86 mil pp / 6.15 mil pp

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 27

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Example #3: General Electric 53 MW Steam Turbine Generator

Bearings #1 - #4 Unfiltered Shaft Relative Orbits 3470 rpm

Turbine Critical Speed at 1797 rpm Rub near Bearing #2 is Re-Exciting the Turbine’s Critical Speed Resulting in a 1/2X Vibration at 3470 rpm

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 28

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Example #3: General Electric 53 MW Steam Turbine Generator

Bearings #1 - #4 Unfiltered Shaft Relative Orbits 3320 rpm

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 29

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Example #4: Kellogg Ammonia Plant; 103-JBT Syn Gas Turbine

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 30

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Example #4: Kellogg Ammonia Plant; 103-JBT Syn Gas Turbine

1X Vector Change due to Rub Modifying Apparent Residual Unbalance

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 31

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Example #5: Mechanical Drive Steam Turbine; 5000 Hp

Approximately 4.5 Minutes Required to Roll through 360⁰

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 32

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Examples #4 and #5

Figure a Figure b Figure c

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 33

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Example #6: 150 MW Steam Turbine Generator

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Example #6: 150 MW Steam Turbine Generator

0.02 0.04 0.06 0.08 0.10 0.12 0.14 T Y X

• 3.00
• 2.00
• 1.00

1.00 2.00 3.00 Y

• 3.00
• 2.00
• 1.00

1.00 2.00 3.00 X T Y X

sec X: 1 mils/div mils

Orbit 9, 10 Waveform Comp ¤ Orbit 9, 10 Waveform Comp X=0.03 sec Y=0.88 mils,-0.52 mils

Y: 5Y 60°L Waveform Comp Direct 2.90 mils X: 5X 30°R Waveform Comp Direct 2.30 mils Company: Nova Scotia Power, Inc. Machine: DF Low Pressure Steam Turbine RPM = 3600 10/28/2010 15:09:03

0.02 0.04 0.06 0.08 0.10 0.12 0.14 T Y X

• 3.00
• 2.00
• 1.00

1.00 2.00 3.00 Y

• 3.00
• 2.00
• 1.00

1.00 2.00 3.00 X T Y X

sec X: 1 mils/div mils

Orbit 11, 12 Waveform Comp ¤ Orbit 11, 12 Waveform Comp X=0.03 sec Y=0.63 mils,-0.68 mils

Y: 6Y 60°L Waveform Comp Direct 3.65 mils X: 6X 30°R Waveform Comp Direct 2.26 mils Company: Nova Scotia Power, Inc. Machine: DF Low Pressure Steam Turbine RPM = 3600 10/28/2010 15:09:03

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 35

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Example #6: 150 MW Steam Turbine Generator

• 10000.00

10000.00 2.00 4.00 6.00

CPM

Full Spectrum 9, 10 ¤

Y: 5Y 30°R X: 5X 60°L Company: Nova Scotia Power, Inc. Plant: Trenton Generating Station JobRef: M10-10-20-01 Machine: DF Low Pressure Steam Turbine RPM = 3600 10/28/2010 15:09:03

• 10000.00

10000.00 2.00 4.00 6.00

CPM

Full Spectrum 11, 12 ¤

Y: 6Y 30°R X: 6X 60°L Company: Nova Scotia Power, Inc. Plant: Trenton Generating Station JobRef: M10-10-20-01 Machine: DF Low Pressure Steam Turbine RPM = 3600 10/28/2010 15:09:03

Reverse Vibration Components Reverse Vibration Components Forward Vibration Components Forward Vibration Components

• 1537
• 1537
• 3600
• 3600

3600 1537 3600 1537

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 36

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• 1. Oil Whirl Characteristic #1: Sub-synchronous vibration rapidly grows and

approaches a value equal to the diametral clearance of the bearing or seal where the whirl is occurring.

• 2. Oil Whirl Characteristic #2: The swirling of the fluid is the primary source for /

cause of fluid induced instability.

• 3. Oil Whirl Characteristic #3: Without pre-swirling, oil whirl occurs at a sub-

synchronous frequency, slightly less than 1/2X, that is equal to the average angular fluid velocity in the bearing or seal.

• 4. Oil Whirl Characteristic #4: Oil whirl is forward precessed (98%+), driven in the

direction of rotation by the tangential force.

• 5. Oil Whirl Characteristic #5: The shape or form of the vibration as observed in

the direct, unfiltered shaft orbit data plot is fully circular with an amplitude limited by the diametral clearance in the bearing or seal.

• 6. Oil Whirl Characteristic #6: Because oil whirl occurs at a sub synchronous

frequency slightly less than ½X, and because it is the primary vibration component, much larger than the 1X, the resulting direct, unfiltered orbit, in addition to being circular in shape, will have 2 Phase Trigger dots on the orbit. Since the frequency is slightly less than ½ X, these Phase Trigger dots will not be fixed on the orbit but will rotate opposite rotation.

Example #6: 150 MW Steam Turbine Generator

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 37

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[Ref 23]

Example #6: 150 MW Steam Turbine Generator

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 38

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Example #7: 20 MW Steam Turbine Generator

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 39

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Example #7: 20 MW Steam Turbine Generator

Steam Turbine Bearings #1 and #2 Vibration Trend Plots Tripped at 1980 turbine rpm During Startup 4.29 mils pp at Bearing #1, Y Probe “Rotor Long” Differential Expansion Reading

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 40

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Example #7: 20 MW Steam Turbine Generator

Turbine Rotor Dynamic Eccentricity - filtered 1X vibration amplitude and phase angle vs. rpm 1.74 mils pp @ 1980 rpm

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 41

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Example #7: 20 MW Steam Turbine Generator

Turbine Rotor Axial Vibration - filtered 1X vibration amplitude and phase angle vs. rpm 4.7 mils pp @ 1980 rpm

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 42

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Example #7: 20 MW Steam Turbine Generator

Turbine Rotor Axial Vibration Trend Plot – 5.22 mils pp @ 1980 rpm

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 43

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Example #7: 20 MW Steam Turbine Generator

Bearings #1 and 2 Orbit / Time Base Data Plots 1979 rpm (turbine) Red Arrow Shows Direction of Preloading During Rub Rub Has Both an Axial and Radial Component

3.79 mil pp / 1.81 mil pp 3.75 mil pp / 3.62 mil pp

[File Name or Event] Emerson Confidential 27-Jun-01, Slide 44

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Example #7: 20 MW Steam Turbine Generator

Full Spectrum Data Plots Bearing #1 Top Bearing #2 Bottom As Rub Commences, Reverse 1X Vibration Components Increase Significantly

Note: Higher order forward and reverse vibration components are due to runout / shaft surface condition and are not indicative of actual vibration

Thank You

Questions?