In Situ Francis Turbine Blade Replacement due to Gross Cavitation

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: 

steven.potter@voith.com 

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 


3

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 inservice 

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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• 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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• 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 


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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 


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Blade removed 

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

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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 1 st 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 

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

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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 


42

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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In Situ Francis Turbine Blade Replacement due to Gross Cavitation

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