Nathan Griffiths - MJB International
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Transcript of Nathan Griffiths - MJB International
www.mjbi.com
THE IMPORTANCE OF CARRYING OUT
GE FRAME ROTOR OVERHAULS &
CONDITION ASSESSMENTS
MJB International
CONTENTS
1. ROTOR OVERHAUL & CONDITION ASSESSMENT.
2. CRITICAL INTERNAL COMPONENTS ONLY ACCESSIBLE DURING FULL
ROTOR DESTACK
3. ISSUES FOUND & RECTIFIED FOLLOWING ROTOR DESTACK.
4. METALLURGICAL INSPECTIONS / NDT DURING DESTACK.
5. ROTOR OVERHAUL FACILITY – CAPABILITIES / EQUIPMENT REQUIRED.
6. SUMMARY / CONCLUSIONS
2
ROTOR OVERHAUL &
CONDITION ASSESSMENT.
SECTION 1
3
ROTOR OVERHAUL &
CONDITION ASSESSMENT
CONDITIONS THAT LIMIT THE LIFE OF THE ROTOR INCLUDE;
• Maintenance Practices
• Operating History
• Foreign Object Damage
• Low cycle fatigue cracking
• Crack initiation / Crack growth
• Material aging / properties
• Creep rupture
THE EFFECTS OF THESE ON THE ROTOR AND ITS COMPONENTS CAN LEAD TO;
• Blade thinning, pitting, erosion
• Disk / Wheel Corrosion
• Creep
• Turbine Wheel Erosion = excessive bucket movement
• Vibrations due to fouling inside the rotor
• Cooling air paths clogging = overheating of HGP parts
EVENTUALLY = ROTOR FAILURE = PROLONGED DOWNTIME + RISK TO
SAFETY OF PLANT & STAFF. 4
ROTOR OVERHAULS
NOT TO BE IGNORED
5
Heavy corrosion on compressor
wheels body.Missing & Damaged Blades Corrosion on distance pieces
Non-standard Balance Weights from
previous overhaul, carried out by
others.Material Blocking Cooling Holes Broken Through Bolt Nut
ROTOR OVERHAUL &
CONDITION ASSESSMENT
This presentation will discuss the importance of Rotor Overhauls & Condition
Assessments for GE Frame Industrial Units (standard tech – B / E Class) utilising MJB’s
extensive rotor overhaul / condition assessment experience:
• 62 x Frame 3002 Rotors
• 157 x Frame 5001 Rotors
• 57 x Frame 5002 Rotors
• 85 x Frame 6 Rotors
• 9 x Frame 7 and 9 Rotors
Other GT rotors overhauled include Siemens V64.3 and ABB11D4/5.
Other rotor experience: MHI & Dresser Rand Centrifugal Compressors, Steam Turbine
Rotors & Generator Rotors (incl. full rewinds).
6
CRITICAL INTERNAL COMPONENTS
ONLY ACCESSIBLE DURING FULL
ROTOR DESTACK
SECTION 2
7
GE FRAME ROTOR ASSEMBLY:
MAIN COMPONENTS
8
MAIN ROTOR COMPONENTS
Compressor Turbine
Forward stub shaft
Discs
Compressor thru bolts
Aft stub shaft
Marriage bolts
Distance piece / Forward stub shaft
Turbine wheels
Wheel spacers
Stud assembly
Aft stub shaft
To carry out full inspection and condition assessment of rotor components, it is
necessary to:
• Fully destack the compressor and turbine rotor
• Mechanical and Metallurgical Inspections of critical internal components
When the rotor assemblies are destacked issues can be corrected immediately.
GE FRAME ROTOR OVERHAUL
WORKSCOPE
9
OVERHAUL WORKSCOPE SUMMARY
1. Incoming Inspection:
• Rotors are externally inspected and prepared for inspection.
• Cleaning, dimensional checks, run-out and balance checks implemented.
Additional / Emerging Works Options will be confirmed - such as: Under Cut of
Journal’s / Thrust collars etc.
2. Compressor / Turbine Rotor Destack:
• Compressor / turbine rotors will be disassembled to their sub assembly components
and visually and mechanically inspected.
3. Condition Assessment – (if required)
• Additional NDT’s – Discussed in further detail later in this presentation.
GE FRAME ROTOR OVERHAUL
WORKSCOPE
10
OVERHAUL WORKSCOPE SUMMARY
4. Compressor / Turbine Repair:
Refurbishment of components will be performed and includes;
• Repair of journals and thrust collar
• Repair of dovetails
• Repair of rabbet areas, marriage areas, rims etc.
• Compressor re-blade
5. Compressor / Turbine Reassembly:
Following inspection and repair procedures, the compressor and turbine rotors will be
reassembled utilizing new hardware.
Customer is welcome to witness key stages of rotor assembly, final balance and run-
out checks.
ISSUES FOUND & RECTIFIED
FOLLOWING ROTOR
DESTACK
SECTION 3
11
COMPRESSOR THRU
BOLT CORROSION / PITTING
ISSUE:
• Thru bolts - subject to moisture =
corrosion pitting.
• Corrosion could result in failure
and high levels of unbalance
during operation.
CORRECTIVE ACTION:
• Replace component.
• Only discovered / resolved
following a full rotor destack.
12
RABBET, BORES AND RIMS FIT WEAR
(DISCS, WHEELS, COUPLING AREAS):
ISSUE:
• Critical these precision interfaces
are maintained to ensure run out
tolerances are achieved.
• If these become loose in service,
high levels of unbalance could
occur.
CORRECTIVE ACTION:
• Re-establish by machining andcoating or installing patch rings.
• Only discovered / resolvedfollowing full rotor destack.
13
INTERNAL COOLING
PASSAGE BLOCKAGES:
ISSUE:
• During operation the rotor ingests
huge quantities of air into the
compressor.
• Environment & Air Filtration issues
= blocked internal cooling passages
= reduced cooling air flow =
premature deterioration of HGP
Parts.
CORRECTIVE ACTION:
• Cleaning & blow through.
• Only discovered / resolvedfollowing full rotor destack.
14
COMPRESSOR BLADE MIGRATION:
ISSUE:
• The spacer holding compressor
blade in position overcomes
staking during start up / shut
down, irregular operating events
causing blade tip contact.
CORRECTIVE ACTION:
• Remove and rework the
spacers
• Only resolved following full
rotor destack.15
COMPRESSOR WHEEL
DOVE SLOT CRACKING:
ISSUE:
• Compressor Wheel Dovetail
Cracking can result in loss of
material causing FOD to
compressor blading & downstream
components.
CORRECTIVE ACTION:
• Blend dovetail cracks.
• Only resolved following a full
rotor destack.
16
THROUGH BOLT CRACKING
ISSUE:
• Through Bolt Nut Failure.
• Example: Fr 5/2 D DLN HP Rotor.
• Resulted in High Vibration.
• RCA determined nuts incorrectly
heat-treated.
CORRECTIVE ACTION:
• Replace all through bolts & nuts.
• Only resolved within a Rotor
Overhaul Facility.
17
FR 9 & FR7 2nd STAGE
DISCOURAGER SEAL DAMAGE
ISSUE:
• FOD & Distortion.
• Allows increased levels of hot
gases to enter into rotor's cavities.
CORRECTIVE ACTION:
• Replace with New Discourager
seal.
• Preferably resolved within a
Rotor Overhaul Facility.18
METALLURGICAL INSPECTIONS /
NDT DURING DESTACK
SECTION 4
19
CONDITION ASSESSMENT
TESTS & ACTIVITIES
• Rotors operational life is finite.
• Exceeding rotor life can result in failures that can damage
the entire turbine.
Condition Assessment NDT:
• Requires rotor to be destacked to gain access to the critical
areas / components.
• Assess material condition to mitigate risk of rotor failure.
20
CONDITION ASSESSMENT
TESTS & ACTIVITIES
21
1ST, 8TH & 16TH STAGE COMPRESSOR WHEELS:
Replication & hardness testing
Ultrasonic inspection 100% surfaces
Magnetic Particle inspection 100% surfaces
Eddy Current Inspection 100% surfaces including bores, fir trees, radii and fillets
DISTANCE PIECE:
Replication & hardness testing
Ultrasonic inspection
Magnetic Particle inspection
Eddy Current Inspection 100% surfaces including bolt holes, radii and fillets
1ST, 2ND & 3RD STAGE TURBINE WHEEL:
Replication & hardness testing of bores and fir trees
Ultrasonic inspection 100% surfaces
Magnetic Particle inspection 100% surfaces
Eddy Current Inspection 100% surfaces including bores, fir trees, radii and fillets
FWD & AFT SHAFTS:
Ultrasonic inspection 100% surfaces
Magnetic Particle inspection 100% surfaces
Eddy Current Inspection 100% surfaces
XRF for material analysis on all components
CONDITION ASSESSMENT
TESTS & ACTIVITIES
VISUAL INSPECTION:
• To examine appearance of rotor surfaces
• As received condition and after cleaning/blasting.
• Examine surface deposits, corrosion, pitting etc. on
rotor, rotor blade surfaces.
SCALE/DEPOSIT ANALYSIS:
Deposits on surfaces of rotor & blading are collected to
determine detrimental elements such as Vanadium,
Potassium, Sulphur etc.
HARDNESS TEST:
• Another method of determining creep damage.
• Changes in hardness can indicate of stress rupture.
• Numbers can be correlated to material ultimate &
yield stress levels.22
CONDITION ASSESSMENT
TESTS & ACTIVITIES
EDDY CURRENT TESTING:
• Performed on turbine wheel, bridge areas, bore hole and stress critical areas.
• Can reveal presence of surface cracks.
ULTRASONIC FLAW DETECTION:
• Performed on the rotor surfaces to detect presence of material flaws, defects or in-depth
cracks.
• High frequency sound waves are introduced into a material.
• Reflected back from surfaces or flaws.23
CONDITION ASSESSMENT
TESTS & ACTIVITIES
MATERIAL VERIFICATION BASED ON XRF ANALYSIS:
• Checks the chemical composition of rotor material.
• Locations = compressor wheels, turbine wheels,
spacers, and distance piece.
MAGNETIC PARTICLE INSPECTION:
Performed on the rotor surfaces to check
for presence of surface or sub-surface
cracks.
24
CONDITION ASSESSMENT
TESTS & ACTIVITIES
IN SITU-METALLOGRAPHY / REPLICATION:
• Replicas taken in known high stress points /areas.
• Examined by Light Optical Microscope & ScanningElectron Microscope (SEM).
• Gold or silver sputtered prior to examining in SEM.
Microexamination will Indicate:
• Major carbide transformations.
• Creep voids and Microcracks (SEM).
Determines Indications of:
• Grain structure change.
• Stability / Comparisons with any previous conditionassessment or a new rotor / component.
25
EXAMPLE OF ISSUES FOUND
26
Phased Array testing to Stage 1 & 2 Compressor Wheels to check nature of defect found
during ultrasonic flaw detection.
• Revealed cluster indications.
• Inherent defects from the manufacturing process (possibly inclusions).
• Measured lengths in the range of 10 to 16 mm.
Defect Areas Located with
Ultrasonic Testing in Compressor
Wheel
EXAMPLE OF ISSUES FOUND
EXAMPLE OF ISSUES FOUND DURING CONDITION ASSESSMENTS :
27
SEM showing Carbide Precipitation in Turbine wheels after 200K+ hrs.
CONDITION ASSESSMENT
TESTS & ACTIVITIES
Success of condition assessment also depends on operating data available,
such as:
• Operating Hours
• Number of starts and stops
• Fuel Fired with fuel analysis
• Any previous failure history
• Any replacements/ refurbishments carried out.
Test results obtained during a rotors full overhaul / condition assessment will
be co-related with the data provided to arrive at the factual condition of the
rotor material and its re-usability.
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ROTOR OVERHAUL FACILITY
– CAPABILITIES / EQUIPMENT
REQUIRED.
SECTION 5
29
CAPABILITIES / EQUIPMENT
REQUIRED.
30
ROTOR OVERHAUL & CONDITION
ASSESSMENT FACILITIES:
Facility should be fully equipped with state of the
art equipment allowing implementation of:
• Complete Inspection
• Condition Assessment
• Overhaul
All performed under one roof = total control &
ownership of scope of work, from receipt through to
dispatch, with no compromise in quality.
Including capabilities to carry out associated
repairs including Bucket Repair, to ensure lead
times are kept to a minimum.
CAPABILITIES / EQUIPMENT
REQUIRED.
31
HORIZONTAL LATHES:
Various capacities up to 30 tonne / 12 metre
bed length to carry out incoming run out
checks.
HORIZONTAL BALANCING:
Various horizontal balance capacity up to 50
tonne / 9.5 metre bed length to carry out
incoming and final rotor balance checks to
OEM specification.
CAPABILITIES / EQUIPMENT
REQUIRED.
CRANES:
Various overhead cranes capacity up to
60 tonne / 12 metre hook height.
STANDS / THROUGH BOLT
STRETCHING EQUIPMENT:
Rotor stands, turning, destack / restack
fixtures and tooling for all GT Frame
sizes up to Fr 9E rotors.
32
CAPABILITIES / EQUIPMENT
REQUIRED.
CLEANING:
Abrasive blast cleaning of compressor &
turbines wheels to remove engine deposits.
(Blast cleaned with 220-aluminum oxide.)
IN-HOUSE LABORATORY:
The workshop repair facility requires support
of an in-house metallurgical laboratory
enabling complete condition assessment.
33
CAPABILITIES / EQUIPMENT
REQUIRED.
WHEEL RUN OUT / STACKING SEQUENCE:
Paragon Circular Geometry Inspection System:
• Utilised by OEM during new rotor manufacture.
• Superior to less accurate wheel run out tables.
Each surface measured approx. 540,000 times,
yielding resolutions to approx. 0.125 microns
Paragon makes all calculations re: Roundness,
Concentricity, Run-Out , Flatness & Parallelism
Plots best wheel position = straightness &
minimizes Total Indicated Runout (TIR) = reducing
rotor imbalance & potential for increased vibration
during operation.34
CAPABILITIES / EQUIPMENT
REQUIRED.
35
COMPRESSOR BLADE REMOVAL & RE-BLADE:
COMPRESSOR BLADE TIP GRINDING:
Blades machined as per specification to ensure
correct clearance once the rotor is installed back
into the GT casing and for optimum compressor
efficiency.
CAPABILITIES / EQUIPMENT
REQUIRED.
VERTICAL BALANCE MACHINES:
Vertical Balance Machine removes
requirement to use 2 x mandrel system
that introduces inaccuracy.
Vertical balance machines custom
designed with expanding mandrels &
high degree of accuracy & repeatability.
Specially designed / manufactured with
sole purpose of balancing GE Frame
Compressor & Turbine wheels.
36
CAPABILITIES / EQUIPMENT
REQUIRED.
ADDITIONAL / OPTIONAL ROTOR REPAIR PROCESSES:
• Thrust Collar Reclamation - repair the collar and return it to original dimensions.
• Under Cut bearing journals - Journal undercutting can be implemented to
customer demands.
• Under Cut Thrust Collars - Thrust collar modification to accommodate new tilting
pad bearing design.
• Probe Track Burnishing – This process incorporates diamond tip machining to
accommodate surface finish required for vibration pick ups
37
CAPABILITIES / EQUIPMENT
REQUIRED.
BUCKET REPAIR & COATING CAPABILITIES:
38
SUMMARY / CONCLUSIONS
SECTION 6
39
SUMMARY / CONCLUSIONS
• Rotor Failure = High Cost implications + Prolonged Downtime + Risk to Safety of Plant &Staff.
• Rotor failures can damage the entire turbine.
• Critical internal components of a rotor are only accessible during full rotor destack.
• When the rotor assemblies are destacked issues can be corrected immediately.
• Rotor overhaul / condition assessment ascertains whether a rotor is suitable to return toservice, based metallurgical examinations / NDT to confirm material condition / suitability.
REQUIRED FACILITY EQUIPMENT / CAPABILITIES:
• Fully equipped with state of the art equipment allowing for Complete Inspection, ConditionAssessment & Overhaul.
• All performed under one roof = total control / ownership of the scope of work from receiptthrough to dispatch, with no compromise in quality.
• Capabilities to carry out associated repairs including Bucket Repair, to ensure lead times arekept to a minimum.
40
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