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Event – Withdrawn After Evaluation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

Unit 1 – MW Output Vs CW Temperature Chart

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 ErosionUnit 2 – MW Output Vs CW Temperature Chart

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 ErosionUnit 1– Predicted RX Power Vs Time

Feedwater Pipe Erosion

Unit 2– Predicted RX Power Vs Time

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 Erosion

Unit 1 Plant Parameter Evaluation

Feedwater Pipe ErosionUnit 2 Plant Parameter Evaluation

Feedwater Pipe ErosionUnit 1 Average Calculated CrossFlow CF Vs Time

Unit 2 Average Calculated CrossFlow CF Vs Time

Feedwater Pipe Erosion

15

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

Original Meter Design

18

Flow Nozzle Replacement

Modified for inspection port and flanges

19

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.

Flow Nozzle Replacement

Sample Isometric of Flow Nozzle

21

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.

Flow Nozzle Replacement

Flow Comparison

24

Flow Nozzle Replacement

Flow Comparison

25

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 ReplacementProposed Design- Removable PTC 6 Nozzle/Recovery Cone Insert

27

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)

Feedwater Nozzle Replacement

30

Selected Replacement Nozzle – Triad ASME PTC-6 LHL Flow Meter Tube