case study t09: applying rotordynamics analysis … › me459 › guest lectures › 2015...
TRANSCRIPT
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APPLYING ROTORDYNAMICS ANALYSIS TO IDENTIFY THE CAUSE OF HIGH SYNCHRONOUS VIBRATION ON OVERHUNG-ROTOR COMPRESSOR
Manuel Marin, ME-MSc Sr. Reliability Engineer Equistar Chemical, LP
Channelview, TX
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Author Bio
• Manuel Marin joined LyondellBasell Industries in Channelview, Texas in 2013 as a Sr. Reliability Engineer and previously, he worked for Dresser-Rand as a Sr. Rotordynamics Engineer, and for PDVSA as Rotating Equipment Engineer. He has over 25 years’ experience, leading several root cause failure analyses and troubleshooting turbomachinery. Mr. Marin is a graduate from Polytechnical University in Venezuela obtaining a B.Sc. degree in Mechanical Engineering. He received a MSc degree in Mechanical Engineering from Texas A&M University. He is a Certified Vibration Analyst Category III, and he is member of the ASME and the Vibration Institute.
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Problem Statement
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• After being overhauled, a one-stage overhung rotor, running at a constant speed rate, showed high vibration on the coupling end during loading.
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Overhung Centrifugal Compressor Overview
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1500 PSIG 670000 SCFM
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Sequence of Events – Relevant Parameters
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• During re-start, bearing-vibration trend plot showed an irregular increase on the inboard end (coupling end) when the unit initiated the loading process.
IB Vib. (V&H): Inboard Bearing Vibration (Vertical & Horizontal) OB Vib. (V&H): Outboard Bearing Vibration (Vertical & Horizontal)
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Sequence of Events - Vibration Data
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• The direct compensated vibration trend plot recorded in the field showed how the vibration at the coupling end was rising up from 0.4 mil Peak-Peak to 2.2 mils Peak-Peak while the unit was loading up at constant speed of 7400 RPM. On the non-drive end, the vibration kept below 0.6 mil Peak-Peak, even after loading the unit.
Direct Compensated
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Sequence of Events - Vibration Data
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• The waterfall plot showed just a 1X component. • The orbit plot on the drive-end probe was pretty round with not
evidence of preload.
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Analysis Approach
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• Based on the severity of the vibration, it was decided to perform a rotordynamics analysis to try to identify the possible causes of the observed behavior.
INPUTS
• M.E.D (Geo Model) • Bearing Dynamics
Coefficients • Unbalance
OUTPUTS
• Critical Speeds • Mode Shapes • Unbalance
Response
Finite Element Based
Rotordynamics Software
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Rotordynamics Analysis - Inputs
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• Rotor Mass Elastic Data (M.E.D.)
LT
Impeller+Nut Weight & Moment of Inertia
Bearing Span
Thrust Collar Weight & Moment of Inertia
CL CL
L6
Half-Coupling Weight &
Moment of Inertia
D: Diameter L: Length CL: Bearing Center Line
D1 D5 , L5
L1 L2 L3
D2 D3 D4
L4
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Bearings Impeller
Thrust Collar Half-Coupling OB Probe IB Probe
Rotordynamics Analysis - Inputs
Geo Model
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• Bearing Characteristics & Dynamic Coefficients Calculation
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Drive-End Bearing (IB)
Non-Drive-End Bearing (OB)
Rotordynamics Analysis - Inputs
Design Radial
Clearance Min: 0.0023” Max: 0.0033”
Min: 0.0025” Max: 0.0035”
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Rotordynamics Analysis - Outputs • Undamped Critical Speed Map – Forward & Backward Modes
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1st Backward Mode
Operating Speed
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Rotordynamics Analysis - Outputs
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• Unbalance Response Comparing Drive-End Bearing Clearance
Increasing in Amplitude @ DE
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Rotordynamics Analysis - Outputs
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• Mode shape @ 7400 RPM Orbits correspond with
field measurement
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Analysis of Results
• The rotordynamics analysis confirmed that the overhung compressor response was sensitive to the coupling-end bearing clearance.
• Having drive-end-bearing clearance bigger than the maximum recommended, created shaft orbits bigger at the coupling end than the ones at the impeller end.
• It was found that a high drive-end bearing clearance could make the first backward mode to become closer to the operating speed range, consequently increasing the vibration at the drive end.
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Solution
• After running at full load conditions, it was confirmed that by using the minimum design bearing clearance at the drive-end bearing, the vibration levels of the overhung rotor were under acceptable values, which was in accordance with the rotordynamics analysis’ results.
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Actual Field Data with Revised IB-Bearing Clearance, Running at Full Load
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Direct Compensated (Full Loaded)
DRIVE-END (IB) Before 2.251 mil P-P After 0.793 mil P-P
Impeller-End (OB)
Drive-End (IB)
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Relevant parameters trend after Revised IB-Bearing Clearance
18 IB Vib. (V&H): Inboard Bearing Vibration (Vertical & Horizontal) OB Vib. (V&H): Outboard Bearing Vibration (Vertical & Horizontal)
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Lesson Learned • This case shows how minor deviations on bearing
clearances can makes big differences on the rotor response.
• Rotordynamic analysis is a useful tool, and it can be applied to real-world situations, helping to understand complex rotating machinery problems.
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