1. Affects of Ultra-Pure Water on Mechanical Seals
Flowserve Flow 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. The Phenomena – Field Observations
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. Where do we encounter this problem?
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. What has been identified as a contributing factor?
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. How these factors interact…. Theoretical Explanation
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. Extremely low conductivity of the water
BACKGROUND INFORMATION
Common denominator in all these applications:
Extremely low conductivity of the water
Electrical conductivity of water types:
Ultra pure water: µS/cm
Distilled water: – µS/cm
Potable water: – µS/cm
Sea water: µS/cm

11. BACKGROUND INFORMATION
Current Test Programs

12. Operating Conditions:
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: ° F
Speed: 430 – 1780 rpm
Test Duration: 200 hours / test

13. Test Plan: CURRENT TEST PROGRAM: (Nuclear)
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. Results (Tungsten Carbide vs. Carbon):
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. Test Results: 200 hours Process fluid: <0.15 µS/cm
CURRENT TEST PROGRAM: (Nuclear)
Test Results: 200 hours Process fluid: <0.15 µS/cm
Field Inspection

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

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

22. Results (Silicon Carbide w/Laser Treatment vs. Carbon):
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