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1
In Situ Francis Turbine Blade
Replacement due to Gross Cavitation
Author: Mr. Steven R. Potter, Sales Manager/ Welding Engineer
Voith Hydro Services Inc., 2885 Olympic Street,
Springfield, OR 98478, USA. Tel: 541-868-1831
Email: [email protected]
Presenter: Steven R. Potter, Sales Manager/Welding Engineer
Voith Hydro Services, Western Region
Original Presentation at 2012 HydroVision, Louisville KY
In Situ Francis turbine Blade Replacement | NWHA Hood River| 2013-05-23
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A brief explanation!
In 2011, when this project, paper and presentation were
started, Peak Hydro Services was a wholly owned
subsidiary of Voith Hydro Inc.
Today Peak Hydro Services is proudly renamed
Voith Hydro Services.
No longer a subsidiary company; is an integral part of
Voith Hydro Inc.’s After Market Business group
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In This Presentation
• Project Facts and History
• Elements and Considerations of the business case
• Powerhouse and Unit Description
• Technical Aspects of Repair • Removal and Replacement of blades
• Results and Conclusions
• Acknowledgements
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Project Facts and History
• Pointe du Bois, Manitoba, Canada – Approximately 95 miles (150 kilometers) North East of Winnipeg, Manitoba, Canada
• On the Winnipeg River
• First Unit in Service: 1911
• Construction Completed: 1926
• Construction Cost: $3.25 Million
• Station Capacity: 78 MW
• Average Annual Generation: 599 kWh
• Waterfall Drop: 45 feet (14 Meters)
• Powerhouse Length: 440 feet (135 Meters)
• Turbine Generators: 15 Double horizontal shaft Francis Turbine Camelback units and 1 Straflo unit
• Project Acquired by Manitoba Hydro in 2002
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Project Facts and History
• Manitoba Hydro is the electric power and natural gas utility in the province of Manitoba, Canada
• Founded in 1961, as a provincial Crown Corporation
• Operates 15 interconnected hydro generating stations
• 527,000 electric power /263,000 natural gas customers
• Acquired Pointe du Bois in 2002; it is the oldest generating station; began operations in 1911
• Initiated plans for $800 million Pointe du Bois modernization in 2007
• Approved to replace the 78MW powerhouse, dam and spillway with a 120-MW powerhouse
• Construction projected to take six years with a planned in-service date of 2015
• This plan was withdrawn in 2011
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Elements and Considerations of the Business Case • Factors discussed are not definitive of Manitoba Hydro’s
business position - represented as some of the project considerations
• With the Powerhouse replacement project cancelled – a smaller project was envisaged
• Business case prepared to repair/restore limited units
• Several runners are grossly cavitated and some with partial loss of blades/band damage
• Several units were shut down for safety
• Some units partially disassembled and or being repaired
• Refurbishment is a multiple year multiple unit project including mechanical, electrical and structural elements
• The business case focused on Unit 13
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Elements and Considerations of the Business Case
• Unit 13 is a double runner horizontal shaft Francis Turbine. The turbine casing consists of two cast iron halves
• Station sees significant seasonal temperature changes which causes rise and fall of the structure and unit alignment issues
• Manitoba Hydro elected not to separate the casing on Unit 13
• Initially attempted cavitation and other repairs in situ using in house employees and internal procedures
• Results and progress resulted in reassessment
• Decided to contract repairs to OEM’s in combination with, specialty hydro repair service providers, MH’s in house labor, engineering and project management teams
• Both Unit 13 turbine runners exhibited extensive and gross cavitation
• Upstream cavitation is worse (all units)
• Runner bands were intact except for cavitation damage
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Pointe du Bois Powerhouse Cross Section
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Elements and Considerations of the Business Case
• Voith Hydro Canada’s Mississauga Ontario division were
contracted with Peak Hydro Services (then a wholly owned
subsidiary of Voith Hydro), now Voith Hydro Services
• Peak (Voith) Hydro Services has more than twenty seven (27)
years dedicated to Hydro Field Machining and Welding
Services – Voith Hydro 135 years
• Concluded the downstream runner of Unit 13 was salvageable
• Upstream runner was in worse condition (true of all upstream
runners at the plant)
• Several blades exhibited gross cavitation with multiple through
holes
• Cavitation so deep preparation to clean sound parent metal not
possible
• Determined that a minimum of three (3) blades would need to be replaced
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Powerhouse Section and Photos
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Summary of the Business Case
• Unit 13 Repair versus Replace
• With significant repair work already performed, completing the
runner repairs was substantially less cost than to replace
• Repair lead time would be approximately half the replacement
time
• Return to service in approximately 14 months
• ROI and time to breakeven were favorable
• Successful repair would demonstrate viability of repairing other
units and contribute to continuing station operations
• Expected to extend unit operating life twenty (20) years
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Overhead view of typical unit with gates in place
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Typical Unit Cross Section
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Runner and Distributor Ring
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Technical Aspects of Repair
• Unit 13 has two Horizontal Francis runners, each 99 inches
diameter
• Both upstream and downstream runners have thirteen (13)
blades
• Each blade had over its life time been repaired multiple times
• Some areas of prior weld repairs were undermined (weld metal
not adhering to base metal) due to improper preparation
• ‘Foreign’ material (rebar) had been included as filler
• All blades were severely cavitated
• Major areas of cavitation on the suction side (typical) of the
blades
• Runner band cavitated adjacent to blade fillets
• Two blades considered unrepairable, a third was marginal
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Typical condition of blades and band
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Technical Aspects of Repair
• Metallurgical samples from runner crowns, bands and blades
revealed chemistry similar to ASTM A27 Grade 70-36
• Highly variable carbon content – classified as Medium Carbon
Steel - Carbon Equivalent (CE) determines weldability
• Repairs costs for in situ cavitation and blade replacements
estimated to be substantially less than replacement runners
• Return the unit to service one year earlier
• Determined that the most cost effective and least risk repair
was removal of three (3) blades by casting replacements
• Blades were 3D Laser Scanned
• Data translated into a CAD model and drawings from which
blades were cast
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Blade prepared for Laser Scan
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Technical Aspects of Repair
• Material and type dependent, castings are readily weldable
• Casting structures of this era (1900-1920) are particularly
prone to variable chemistry and are very porous
• Water immersion of the components allows moisture to migrate
throughout the casting filling those voids and pores
• Moisture in the substrate not conducive to high quality defect
free welding product
• Trapped water pockets will flash to steam at exposure to the
extreme temperatures of fusion welding
• Gases become entrapped in the weld metal
• Concern with the presence of entrapped water is the
probability of hydrogen embrittlement of the material
• Moisture must be removed
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• Under magnification the
structure can in places be seen
to be a loosely joined series of
voids
• When submerged are
eventually filled with water.
• The Pointe du Bois runner
castings contain gas pockets,
pores, voids and casting dross
(impurities)
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Technical Aspects of Repair
• Primary welding process for all areas was Flux Core Arc
Welding (FCAW), a derivative process of GMAW (MIG) welding
• Repairs abutting prior repair zones required special
consideration as they contain surface and subsurface
discontinuities
• Random discontinuities found at repair margins
• Selectively used Gas Tungsten Arc Welding process (GTAW)
• The skills applied by the welders proved very successful
eliminating defects and providing acceptable repairs
• Acceptance criteria established by Voith Hydro and Manitoba
Hydro for the new repairs
• In process inspections using liquid dye penetrant
• Linear indications subject to Magnetic Particle Inspection
• All inspections were witnessed by Manitoba Hydro
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Technical Aspects of Repair
• Blades measure 46” inches long by 16” wide
• Thickness approximately 0.75” inches at leading and trailing
edges; 1.25” at middle sections
• Average repaired area 160 square inches some exceeding 250
square inches
• Cavitation generally exceeded 0.300” deep
• Some areas greater than 1.00” deep
• Blades mapped prior to repair (as found condition)
• Mapped repairs (as left condition) and photographed
• Blade vent openings measured before and after welding
• Band gap clearance and run out was measured
• Unit 13 downstream runner repaired while replacement blades
for the upstream runner were being cast
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Typical ‘as found’ condition
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Typical ‘as left’ condition
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Removal and Replacement of blades in situ
• Upstream cavitation repair before replacement blades
• During repairs it was decided that one of the three (3) blades
identified for replacement was actually salvageable
• Substantial time, discussion and engineering was expended
prior to any site work in order to plan methods to remove,
replace and inspect the blades
• Peak Hydro determined the best solution was using butt weld
preparations as opposed to the natural fillet conjunction of
band, crown and the blades in the ‘as cast’ configuration
• Post weld inspection (using ultra sound) of fillets would detect
anomalies inherent to the casting
• Butt joints are easier to prepare for weld processing and
provide a ‘cleaner’ inspection zone
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Prior repair at Blade/Band fillet
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Gouging of fillet reveals voids
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Removal and Replacement of blades in situ
• Repair and overlay was completed in four junction zones;
suction and pressure sides of fillets at band and crown
• A lifting plan was prepared (safe work plan)
• Each section of blade being removed/replaced weighed
approximately 200 Lbs.
• Chain blocks and restraining/locating plinths were welded to
adjacent blades to ensure that when cut free the blade would
not slip out of position
• Blades were plasma cut and lowered from the 6 O’clock
position
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Blade prepared for removal
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Blade fillets repaired
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Blade Removal and replacement
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Blade is lowered from runner
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Old/New blades compare and trim
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36 Presentation name | place or presenter | YYYY-MM-DD
Blade removed
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Removal and Replacement of blades in situ
• Blade stubs were prepared with a double V weld preparation
geometry and inspected prior installation
• The replacement blades were fitted in place and welded
according to qualified sequence and weld procedures
• Subjected to ultrasonic inspections by a third party inspection
company
• Three of four (3 of 4) welds passed 1st inspection
• One of four (1 of 4) required repair before being accepted to
ASME VIII standards on re-inspection
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Prepare stubs for replacement blade
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New blade being installed
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Ultra Sonic Inspection of replacement blades
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Repair Results and Conclusions
• Welding repairs to both downstream and upstream runners
have proven very successful restoring structure integrity, blade
thickness, profile and fairness
• While still a blend of old and new repairs, the surface area of
quality weld material has substantially increased particularly in
areas prone to cavitation
• All major structural defects have been repaired
• All cavitation has been removed
• The removal and replacement of blades worked according to
planned procedure without issues
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Repair Results and Conclusions
• Vent openings measured between each blade set
• Hydraulic Balance measured as percentage from nominal
• ‘As Found’ measurements not considered reliable due to the
poor condition of the blade surfaces
• Averaged 0.85% for the downstream and -0.36% for the
upstream
• ‘As Left’ measurements reveal hydraulic balance has improved
to 0.08% downstream and -0.05% upstream
• The two blades replaced in situ were subjected to full NDT
examination in addition to dimensional checks and found to be
acceptable to ASME VIII standards
• Runner integrity, hydraulic balance and fairness are all
substantially improved
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Acknowledgements:
The following persons all made major contributions to the
success of the Pointe du Bois project:-
Manitoba Hydro: Messrs. Jules Gareau, Jeff Marshall,
Dan Nahuliak, Rejan Sayak
Voith Hydro Services: Messrs. Samuel Perry, Steven Potter
Christopher Vaughan, Michael Norris
Voith Hydro Canada: Messrs. Richard Deboo,
Charles Gagnon, Mehrzad Shahouei
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Thanks for your attention
Voith Hydro Services
In Situ Francis turbine Blade Replacement | NWHA Hood River| 2013-05-23