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

Back to Basics – Rubbing or Not? Presented by: G. Richard Thomas, P.E. Principal Engineer SETPOINT ™ Minden, NV USA Vibration Institute Piedmont Chapter 26 June 2015

Historical Perspective Machinery Diagnostics Data Acquisition System Circa April 1984 [File Name or Event] Emerson Confidential 2 26 June 2015 27-Jun-01, Slide 2

Machinery Diagnostics Data Acquisition System Circa April 2015 [File Name or Event] Emerson Confidential 3 26 June 2015 27-Jun-01, Slide 3

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 4 26 June 2015 27-Jun-01, Slide 4

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 5 26 June 2015 27-Jun-01, Slide 5

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 Y casing 1. Y shaft 5 . DC Gap volts 2 . Phase 4 . Shape 1.b 1X or nX Amplitude Phase Trigger 3 . Frequency Once-per-turn event [Ref 23] [File Name or Event] Emerson Confidential 6 26 June 2015 27-Jun-01, Slide 6

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 7 26 June 2015 27-Jun-01, Slide 7

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 8 26 June 2015 27-Jun-01, Slide 8

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 9 26 June 2015 27-Jun-01, Slide 9

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. [File Name or Event] Emerson Confidential 10 26 June 2015 27-Jun-01, Slide 10

Example #1: W501D5A Industrial Frame Gas Turbine / Generator [File Name or Event] Emerson Confidential 11 26 June 2015 27-Jun-01, Slide 11

Example #1: W501D5A Industrial Frame Gas Turbine / Generator 9.47 mil pp / 5.62 mil pp Bearing #1 105 MW 5.17 mil pp / 5.09 mil pp Bearing #2 105 MW [File Name or Event] Emerson Confidential 12 26 June 2015 27-Jun-01, Slide 12

Example #1: W501D5A Industrial Frame Gas Turbine / Generator 13 mil pp 8.4 mil pp [File Name or Event] Emerson Confidential 13 26 June 2015 27-Jun-01, Slide 13

Example #1: W501D5A Industrial Frame Gas Turbine / Generator [File Name or Event] Emerson Confidential 14 26 June 2015 27-Jun-01, Slide 14

Example #1: W501D5A Industrial Frame Gas Turbine / Generator [File Name or Event] Emerson Confidential 15 26 June 2015 27-Jun-01, Slide 15

Example #2: Westinghouse 271 MW Steam Turbine / Generator [File Name or Event] Emerson Confidential 16 26 June 2015 27-Jun-01, Slide 16

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 17 26 June 2015 27-Jun-01, Slide 17

Example #2: Westinghouse 271 MW Steam Turbine / Generator [File Name or Event] Emerson Confidential 18 26 June 2015 27-Jun-01, Slide 18

Example #2: Westinghouse 271 MW Steam Turbine / Generator [File Name or Event] Emerson Confidential 19 26 June 2015 27-Jun-01, Slide 19

Example #2: Westinghouse 271 MW Steam Turbine / Generator [File Name or Event] Emerson Confidential 20 26 June 2015 27-Jun-01, Slide 20

Example #2: Westinghouse 271 MW Steam Turbine / Generator [File Name or Event] Emerson Confidential 21 26 June 2015 27-Jun-01, Slide 21

Example #2: Westinghouse 271 MW Steam Turbine / Generator [File Name or Event] Emerson Confidential 22 26 June 2015 27-Jun-01, Slide 22

Example #3: General Electric 53 MW Steam Turbine Generator [File Name or Event] Emerson Confidential 23 26 June 2015 27-Jun-01, Slide 23

Example #3: General Electric 53 MW Steam Turbine Generator Bearings #1 - #4 Unfiltered Shaft Relative Orbits 3380 rpm [File Name or Event] Emerson Confidential 24 26 June 2015 27-Jun-01, Slide 24

Example #3: General Electric 53 MW Steam Turbine Generator Bearings #1 - #4 Unfiltered Shaft Relative Orbits 3530 rpm [File Name or Event] Emerson Confidential 25 26 June 2015 27-Jun-01, Slide 25

Example #3: General Electric 53 MW Steam Turbine Generator 4.86 mil pp / 6.15 mil pp Bearings #1 - #4 Unfiltered Shaft Relative Orbits 3565 rpm [File Name or Event] Emerson Confidential 26 26 June 2015 27-Jun-01, Slide 26

Example #3: General Electric 53 MW Steam Turbine Generator Bearings #1 - #4 Unfiltered Shaft Relative Orbits Turbine Critical Speed at 1797 rpm 3470 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 26 June 2015 27-Jun-01, Slide 27

Example #3: General Electric 53 MW Steam Turbine Generator Bearings #1 - #4 Unfiltered Shaft Relative Orbits 3320 rpm [File Name or Event] Emerson Confidential 28 26 June 2015 27-Jun-01, Slide 28

Example #4: Kellogg Ammonia Plant; 103-JBT Syn Gas Turbine [File Name or Event] Emerson Confidential 29 26 June 2015 27-Jun-01, Slide 29

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 30 26 June 2015 27-Jun-01, Slide 30

Example #5: Mechanical Drive Steam Turbine; 5000 Hp Approximately 4.5 Minutes Required to Roll through 360 ⁰ [File Name or Event] Emerson Confidential 31 26 June 2015 27-Jun-01, Slide 31

Examples #4 and #5 Figure a Figure b Figure c [File Name or Event] Emerson Confidential 32 26 June 2015 27-Jun-01, Slide 32

Example #6: 150 MW Steam Turbine Generator [File Name or Event] Emerson Confidential 33 26 June 2015 27-Jun-01, Slide 33