Affects of Ultra-Pure Water on Mechanical Seals Presented By : Pat Prom Prepared By :

1. FlowserveFlow Solutions Group Affects of Ultra-Pure Water on Mechanical Seals Presented By: Pat Prom Prepared By: James Saucerman Art Olson

2. Summary: • Background Information • Current Test Programs: • -Reactor Recirculation Pumps • -Reactor Feedwater Pumps • The Solution

3. Background

4. BACKGROUND INFORMATION • The Phenomena – Field Observations • Under certain operating conditions and environment a specific kind of damage occurs to both silicon carbide and tungsten carbide. • Certain areas on a silicon carbide seal face experience pitting/chipping and material loss. In tungsten carbide the result also exhibits pitting and flow channels.

5. BACKGROUND INFORMATION(Field Results – Spectrum Analysis of SiC)

6. BACKGROUND INFORMATION(Field Results –Cross-Section Tungsten Carbide) Nickel binder removed leaving voids in material Original condition of tungsten carbide with nickel binder present

7. BACKGROUND INFORMATION • Where do we encounter this problem? • Nuclear primary reactor recirculation pumps • Increasing number of incidents in BWR plants worldwide • Reactor Feed Water Pumps • Fossil fueled plants worldwide using COT (Combined Oxygen Treatment) • More conventional plants going to ultra-pure water are increasing the number of seals experiencing this problem

8. BACKGROUND INFORMATION • What has been identified as a contributing factor? • Purity of process fluid (Ultra-pure water) • Friction • Piezoelectric properties of silicon carbide or tungsten carbide • High circumferential speeds

9. BACKGROUND INFORMATION • How these factors interact…. Theoretical Explanation • Seal face friction generates heat and charged particles on seal surfaces. • In the presence of low conductivity water the electrical charges can not easily dissipate and charge builds on SiC or Wc seal face. • When sufficient charge accumulates the stored energy jumps or travels to a conducting surface; resulting in the damage to the outer diameter of the rotating face. • Discharging results in vaporized regions at the sub-micron level which grow over time (SiC) or loss of binder in Wc

10. BACKGROUND INFORMATION Common denominator in all these applications: Extremely low conductivity of the water Electrical conductivity of water types: Ultra pure water: 0.055 µS/cm Distilled water: 0.3 – 5.0 µS/cm Potable water: 30 – 1500 µS/cm Sea water: 50000 µS/cm

11. BACKGROUND INFORMATION Current Test Programs

12. CURRENT TEST PROGRAM: (Nuclear) • Operating Conditions: • Seal: 9” balance diameter • Material Selections: • Tungsten Carbide vs. Carbon • SiC w/laser treatment vs. Carbon • Test Fluid: • Distilled water (20 – 65 µS/cm) • Ultra-pure water (< 0.15 µS/cm) • Fluid Temperature: 75 - 160° F • Speed: 430 – 1780 rpm • Test Duration: 200 hours / test

13. CURRENT TEST PROGRAM: (Nuclear) • Test Plan: • 3 Rapid Pressure Transient Cycles: 15 – 1025 psig • (2 hours) • 2 Rapid Temperature Transients: 60 – 160° F • (1 hour) • Various operating speeds: • Slow Roll Speed: 430 rpm • (1st 100 hours of test) • Full Speed 1780 rpm • (2nd 100 hours of test)

14. CURRENT TEST PROGRAM: (Nuclear) Results (Tungsten Carbide vs. Carbon): Electro-corrosion Process fluid: 20 – 65 µS/cm Process fluid: 0.065 – 0.12 µS/cm

15. CURRENT TEST PROGRAM: (Nuclear) Test Results: 200 hours Process fluid: <0.15 µS/cm Field Inspection

16. CURRENT TEST PROGRAM: (Reactor Feedwater Pump) • Operating Conditions: • Test Fluid: • Distilled water (20 – 30 µS/cm) • Ultra-pure water (< 0.15 µS/cm) • Fluid Temperature: 125° F • Speed: 5500 rpm • Test Duration: 168 hours • Flow Rate: 5 gpm

17. CURRENT TEST PROGRAM: (Reactor Feedwater) AISI 316 Sleeves WC SiC

18. The Solution

19. Low amplitude waves: Improves hydrodynamic stability and increases load support THE SOLUTION: Precision Face Topography w/Laser Treatment Seal dam: Maintains low leakage Full Laser Treatment: Changes material and electrical properties Self-Cleaning Design: Expels suspended solids in process fluid

20. THE SOLUTION: Precision Face Topography w/Laser Treatment Lasered processed SiC face Standard lapped SiC face

21. TEST RESULTS: (Fossil Fuel) Results (Silicon Carbide w/Laser Treatment vs. Carbon): Original Design after 168 hours Proposed Design after 430 hours

22. TEST RESULTS: (Nuclear) Results (Silicon Carbide w/Laser Treatment vs. Carbon): Process fluid: 20 – 73 µS/cm Process fluid: 0.075 – 0.14 µS/cm

23. CONCLUSIONS: Precision Face Topography w/Laser Treatment • Electro-corrosion (EC) does not occur above 20 µS/cm process fluid; field experience shows above 15 µS/cm • Field experience and tests show that the purer the water the more aggressive the damage becomes • The use of hydro-dynamic features + post laser processing of surface eliminates EC in ultra-pure water applications • Combination of hard-soft seal faces are forgiving for wider range of operating conditions and allows incidental contact at smaller fluid film thickness (lower leakage)

24. CONCLUSIONS: Precision Face Topography w/Laser Treatment • Matching electrical conductivity of sealing surface pair will minimize the build-up of electrical charge, minimizing the potential between the two surfaces • Precision Face Topography w/laser treatment provides cooler running face temperatures which minimizes likelihood of electro-corrosion

25. FUTURE WORK: Precision Face Topography w/Laser Treatment • Perform long term testing on steady state nominal operation tests for both reactor recirculation and Reactor Feed Water pump seals