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Feedwater System Reliability Users Group
2015 MeetingSan Antonio
James Alston – South Texas Project
Rob Frazee – South Texas Project
Frank Todd – True North Consulting, LLC
Ken Porter – True North Consulting, LLC
STP Feedwater Pipe Erosion and Nozzle
Replacement Options
Feedwater Pipe Erosion
• Discovery of Pipe Wall Thinning• Erosion of the main feedwater piping in the
area of the CrossFlow Transducers• Discovered in December 2013• LER submitted January 2014 For Overpower
Event – Withdrawn After Evaluation
• Compensatory Actions • Revised pipe wall thickness values inserted
in flow computer• Compensate for change in flow area• Mitigate any possible overpower condition
Feedwater Pipe Erosion
Assumption◦Erosion Occurred Slowly Over Time◦Any Power Change Would Also Occur
Over TimeMethodology
Analysis Would Have To Include Data From Multiple Cycles To Pick-up Suspected Change In Indicated RX Power
Feedwater Pipe Erosion
Three Evaluation Methods Chosen◦MW Output Vs CW Temperature (Multiple
Cycles) Assumes Steady Operation From Cycle To Cycle Assumes No Other Significant TP Events
◦True North Power Predictor Utilizes A “Best Estimate Statistical Analysis”
Method Assumes Valid Baseline Data Is Available
◦Analysis Of HP Turbine Parameters Over Time Assumes Good Operation
Feedwater Pipe Erosion
Significant Issues In Unit 1 DataData Not Available Prior To Cycle 12Cycles 12-13 Combined (Prior To LP Turbine
Retrofit)Cycle 15 Data Split To Show Impact of
Extraction Steam Bellows FailureCycle 17 Data A Clear Outlier
◦ Problem With MW Transducer During CycleCycle 18 Htr 15c Extraction Line IssueCycle 18 Significant Reduction In Plant Output
When New Pipe Wall Thickness Value Inserted In January 2014
Feedwater Pipe Erosion
Significant Issues In Unit 2 Data
Data Not Available Prior To Cycle 10Cycles 10-12 Combined (Prior To LP Turbine
Retrofit)Cycle 14 Data Split To Show Impact of
Extraction Steam Bellows FailureCycle 17 Significant Reduction In Plant
Output When New Pipe Wall Thickness Value Inserted
Feedwater Pipe ErosionPAA (Polyacrylic Acid) Injection Evaluation◦Unit 1 Began Injection In Cycle 16
(Dec. 2010) ◦Unit 2 Began Injection In Cycle 15
(Feb 2011)No Evidence That PAA Injection Caused A Change In Flow Measurement
Feedwater Pipe ErosionUnit 1 Average Calculated CrossFlow CF Vs Time
Unit 2 Average Calculated CrossFlow CF Vs Time
Feedwater Pipe Erosion• Conclusions
• No Overpower Event Despite Erosion• Suspect Change In Pipe Wall
Roughness Resulted In Flow Profile Change
Flow Nozzle Replacement
Original Meter Design◦ Nom. pipe size = 18.00 in.◦ Pipe I.D. = 15.250 in.◦ Nozzle throat I.D. = 8.0063 in.◦ Ref. Temp. = 68 Deg. F◦ Carbon steel pipe◦ Stainless steel nozzle and downstream portion of
recovery cone◦ Carbon steel end of recovery cone◦ Angle of divergence of recovery cone (from
centerline) = 6 Deg. 30 Min.◦ Three tap sets, 120 Deg. apart.◦ Upstream taps have stainless steel tube inserts
with 0.25” I.D.◦ Throat taps are 0.25” I.D. and connected to outside
pipe taps by internal tubing.17
Flow Nozzle Replacement
Difficult Access
20
Piping plan view of the area around the feedwater flow nozzles. The feedwater flow nozzles are wedged in below some larger piping. Part of the meter runs are also located above the diesel generating room.
Nozzle Error Modes
22
Upstream fouling or erosion – roughness & diameter effects
Upstream erosion around tap
Leaking throat tap
Nozzle fouling– roughness effects Drain
hole erosion
Failure of nozzle attachment point
Throat Tap irregularities
Flow Nozzle Replacement
Upstream Tap Condition – Possible Effects
23
• Possible higher pressure measurement on the upstream tap due to pipe diameter change and localized turbulence could result in a higher dp measurement at a given flow rate.
• Plant data indicates that the overall effect was in the conservative direction.
Feedwater Nozzle ReplacementProposed Design Options
◦ Removable PTC 6 Nozzle/Recovery Cone Insert◦ Welded-in Flow Nozzle/Recovery Cone Meter Tube◦ Flanged Low Head Loss Nozzle Meter Tube
Other Options Considered◦ Universal Venturi Tube◦ ASME Classical Venturi◦ High Head Recovery Meter Tube
26
Feedwater Nozzle Replacement◦Welded-in Flow Nozzle/Recovery
Cone Meter Tube or Flanged Low Head Loss Nozzle Meter Tube (similar design but shorter length)
28
Feedwater Nozzle Replacement
29
Design Cost Uncertainty
Removable PTC 6 Nozzle/Recovery Cone
60 -100K plus calibration
0.2% to 0.3% (meets almost all ASME Specs)
Welded-in Flow Nozzle/Recovery Cone
180K plus calibration
0.2% to 0.3% (meets all ASME Specs)
Low Head Loss Meter Tube 94K plus calibration
0.5% (does not meet all ASME Specs)