Back to Basics Rubbing or Not? - Vibration to Basics_Rubbing or Not_PPT... · Presented by: G....

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

http://www.vi-institute.org/

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

26 June 2015

Historical Perspective

Machinery

Diagnostics

Data Acquisition

System Circa

April 1984



26 June 2015

Machinery Diagnostics Data Acquisition System Circa April 2015



26 June 2015

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



26 June 2015

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



26 June 2015

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]



26 June 2015

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.



26 June 2015

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.



26 June 2015

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.



26 June 2015

Introduction

• The frictional forces that are present during a rub produce local heating of 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.



26 June 2015

Example #1: W501D5A Industrial Frame Gas Turbine / Generator



26 June 2015


Bearing #2 105 MW

Bearing #1 105 MW

9.47 mil pp / 5.62 mil pp




26 June 2015


13 mil pp

8.4 mil pp



26 June 2015




26 June 2015

Example #2: Westinghouse 271 MW Steam Turbine / Generator



26 June 2015


• 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.



26 June 2015




26 June 2015

Example #3: General Electric 53 MW Steam Turbine Generator



26 June 2015


Bearings #1 - #4

Unfiltered Shaft Relative Orbits

3380 rpm



26 June 2015


Bearings #1 - #4


3530 rpm



26 June 2015


Bearings #1 - #4


3565 rpm




26 June 2015


Bearings #1 - #4


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



26 June 2015


Bearings #1 - #4


3320 rpm



26 June 2015

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



26 June 2015

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

1X Vector Change due to Rub Modifying

Apparent Residual Unbalance



26 June 2015

Example #5: Mechanical Drive Steam Turbine; 5000 Hp

Approximately 4.5 Minutes Required to Roll through 360⁰



26 June 2015

Examples #4 and #5

Figure a

Figure b

Figure c



26 June 2015

Example #6: 150 MW Steam Turbine Generator



26 June 2015


0 0.02 0.04 0.06 0.08 0.10 0.12 0.14

T

Y

X

-3.00

-2.00

-1.00

0

1.00

2.00

3.00 Y-3.00

-2.00

-1.00

0

1.00

2.00

3.00 X

T

Y

X

sec

X: 1 mils/div

mils

Y:

1 m

ils/d

iv

Orbit 9, 10 Waveform Comp¤

Orbit 9, 10 Waveform CompX=0.03 secY=0.88 mils,-0.52 mils

Y: 5Y 60°L Waveform Comp Direct 2.90 milsX: 5X 30°R Waveform Comp Direct 2.30 milsCompany: Nova Scotia Power, Inc.Machine: DF Low Pressure Steam Turbine RPM = 360010/28/2010 15:09:03

0 0.02 0.04 0.06 0.08 0.10 0.12 0.14

T

Y

X

-3.00

-2.00

-1.00

0

1.00

2.00

3.00 Y-3.00

-2.00

-1.00

0

1.00

2.00

3.00 X

T

Y

X

sec

X: 1 mils/div

mils

Y:

1 m

ils/d

iv

Orbit 11, 12 Waveform Comp¤

Orbit 11, 12 Waveform CompX=0.03 secY=0.63 mils,-0.68 mils

Y: 6Y 60°L Waveform Comp Direct 3.65 milsX: 6X 30°R Waveform Comp Direct 2.26 milsCompany: Nova Scotia Power, Inc.Machine: DF Low Pressure Steam Turbine RPM = 360010/28/2010 15:09:03



26 June 2015


-10000.00 0 10000.000

2.00

4.00

6.00

CPM

Ma

g, m

ils

, m

ils

(p

k-p

k)

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 0 10000.00

0

2.00

4.00

6.00

CPM

Ma

g, m

ils

, m

ils

(p

k-p

k)

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



26 June 2015

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.




26 June 2015

[Ref 23]




26 June 2015




26 June 2015


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



26 June 2015


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



26 June 2015


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



26 June 2015


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



26 June 2015


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





26 June 2015


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?


Back to Basics Rubbing or Not? - Vibration to Basics_Rubbing or Not_PPT... · Presented by: G....

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