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Affects of Ultra-Pure Water on Mechanical Seals
Presented By:Pat Prom
Prepared By:James SaucermanArt Olson
FlowserveFlow Solutions Group
Summary:
• Background Information
• Current Test Programs:
-Reactor Recirculation Pumps
-Reactor Feedwater Pumps
The Solution
Background
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.
BACKGROUND INFORMATION
BACKGROUND INFORMATION(Field Results – Spectrum Analysis of SiC)
BACKGROUND INFORMATION(Field Results –Cross-Section Tungsten Carbide)
Nickel binder removed leaving voids in material
Original condition of tungsten carbide with nickel binder present
BACKGROUND INFORMATION
Where do we encounter this problem?
1. Nuclear primary reactor recirculation pumps Increasing number of incidents in BWR plants worldwide
2. Reactor Feed Water Pumps
3. 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
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
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
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
BACKGROUND INFORMATION
Current Test Programs
BACKGROUND INFORMATION
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
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)
CURRENT TEST PROGRAM: (Nuclear)
CURRENT TEST PROGRAM: (Nuclear)
Results (Tungsten Carbide vs. Carbon):
Process fluid:
20 – 65 µS/cm
Process fluid:
0.065 – 0.12 µS/cm
Electro-corrosion
Test Results: 200 hours Process fluid: <0.15 µS/cm
Field Inspection
CURRENT TEST PROGRAM: (Nuclear)
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
SiC
WC
AISI 316 Sleeves
CURRENT TEST PROGRAM: (Reactor Feedwater)
The Solution
THE SOLUTION: Precision Face Topography w/Laser Treatment
Low amplitude waves:
Improves hydrodynamic stability and increases load support
Self-Cleaning Design:
Expels suspended solids in process fluid
Seal dam:
Maintains low leakage
Full Laser Treatment:
Changes material and electrical properties
THE SOLUTION: Precision Face Topography w/Laser Treatment
Standard lapped SiC face Lasered processed SiC face
TEST RESULTS: (Fossil Fuel)
Results (Silicon Carbide w/Laser Treatment vs. Carbon):
Original Design after 168 hours
Proposed Design after 430 hours
TEST RESULTS: (Nuclear)
Results (Silicon Carbide w/Laser Treatment vs. Carbon):
Process fluid:
0.075 – 0.14 µS/cm
Process fluid:
20 – 73 µS/cm
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)
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
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