in situ francis turbine blade replacement due to gross ... · pdf file1 in situ francis...

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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


6 In Situ Francis turbine Blade Replacement | NWHA Hood River| 2013-05-23

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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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• 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


20 In Situ Francis turbine Blade Replacement | NWHA Hood River| 2013-05-23

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• 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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• 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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• 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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• 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


36 Presentation name | place or presenter | YYYY-MM-DD

Blade removed

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• 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


39 Presentation name | place or presenter | YYYY-MM-DD

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


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