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

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

Background

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.

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

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

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

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

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: 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

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: 75 - 160° F Speed: 430 – 1780 rpm Test Duration: 200 hours / test

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)

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

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

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

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

The Solution

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

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

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

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

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