ML13316B905
| ML13316B905 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 11/13/2013 |
| From: | Taplett K South Texas |
| To: | Division of License Renewal |
| Daily J | |
| References | |
| Download: ML13316B905 (45) | |
Text
SOUTH TEXAS PROJECT ALUMINUM BRONZE TESTING UPDATE November 13, 2013 1
11/13/2013
Agenda
- Introductions
- Purpose
- AlBrz Dealloying Background
- Testing Protocols
- Preliminary AlBrz Testing Results
- Future Testing Plans
- AlBrz Dealloying Program Development
- Summary
- Questions 2
11/13/2013
South Texas Project (STP) Attendees
- Michael Berg - Manager, Design Engineering
- Michael Murray - Manager, Regulatory Affairs
- Rob Engen - Manager, Engineering Projects
- Arden Aldridge - License Renewal Project Manager
- Ken Taplett - Supervisor, Licensing
- Matthew Hiatt - Aluminum Bronze Project Engineer
- Fred Puleo - Licensing Engineer
- Richard Kersey - Supervisor, Civil Design Engineering
- Cong Pham - Supervisor, Mechanical Design Engineering
- Kevin Regis - ECW System Engineer
- Aaron Heinrich - Aluminum Bronze Program Engineer
- Suryakant Sam Patel - Contractor
- Russ Cipolla - Contractor, Intertek AIM (Aptech) 3 11/13/2013
Purpose
- Describe the progress of testing completed by STP on aluminum bronze components in support of License Renewal activities
- Describe the future testing scope to be completed by STP in 2014
- Describe development of program procedure to manage and analyze aluminum bronze dealloying 4
11/13/2013
AlBrz Dealloying Background
- Metallurgy
- Aluminum bronze alloy is composed of alpha, beta and gamma-2 phases depending on aluminum content and heat treatment
- Gamma-2 phase and beta phase preferentially corrode and leach out aluminum. Result is a porous structure that can result in a through-wall leak if gamma-2 or beta network is continuous through material
- Heat treatment for castings determines if network is continuous and whether alpha+gamma-2 eutectoid or alpha+beta eutectoid forms 5
Typical Microstructure A - copper-rich alpha matrix B - alpha-gamma2 eutectoid C - isolated, preferentially attacked gamma-2 (dark regions within the eutectoid and along the grain boundaries) 11/13/2013
AlBrz Dealloying Background (continued)
- Dealloying Propagation There is a discontinuity in microstructure at the boundary between dealloyed regions and undealloyed regions in a component. This discontinuity in microstructure can be explained by the dealloying process which slowly proceeds across the component pressure boundary. As the corrosion process created by the wetted surface extends through the thickness, the Al-Brz continues to dealloy along the wetted path. The remaining wall thickness is not affected by the corrosion process until it contacts the corrosive environment. The boundary between the two material states (dealloyed / undealloyed) is not very wide and defines the depth of the dealloying in the specimen.
- Dealloying is measured / identified by etching surfaces with silver nitrate - darker regions denote dealloyed areas
- Degree of dealloying (% dealloying) is a geometrical measure
= Depth of dealloying / component wall thickness OR
= Area of dealloying / total component cross-sectional area 11/13/2013 6
AlBrz Dealloying Background (continued)
- Essential Cooling Water (ECW) System is constructed of aluminum bronze alloys
- SB169 CA614
- Wrought, single-phase alloy, 6.0 - 8.0% Al by weight
- Used for pipe, fittings and small-bore valves
- Not susceptible to dealloying
- SB148/271 CA 952/954
- Cast, alpha+beta+gamma-2 phase
- CA952 - 8.5%-9.5% Al by weight,
- CA954 - 10.0-11.5% Al by weight
- Used for fittings, large-bore valves, pumps
- Susceptible to dealloying 7
11/13/2013
AlBrz Dealloying Background (continued)
- History at STP
- Dealloying initially identified at STP during plant construction/start-up through large number of leaking small-bore cast fittings
- All small-bore (< 3 NPS) castings have been replaced with wrought
- Established methods to evaluate through-wall leaks in large-bore castings for operability/structural integrity
- Captured in UFSAR Appendix 9A and supporting calculations
- Long-term management by Leak-Before-Break
- Number of Through-Wall Leaks per Year
- Large-bore castings 5/yr at startup, 1-2/yr currently 8
11/13/2013
AlBrz Dealloying Background (continued)
- Susceptible Component Population
- 251 flanges, 1 reducer, 1 cap, 1 elbow and 19 tees
- Bulk of through-wall leaks have been at flanges
- 151 valves and 12 pumps
- Mostly above and below ground piping butt-welds
- Non-Susceptible Component Population
- All pipe is wrought
- All below-grade fittings are wrought
- All small-bore (<3 NPS) components were replaced with wrought in 1988-1990 timeframe
- Most large-bore castings that leaked were replaced with wrought
- Some leaking valves were replaced with cast material 9
11/13/2013
AlBrz Dealloying Background (continued)
- STP has procured large number of non-susceptible spare fittings and valves to enable rapid replacement of leaking components when identified
- Replacement flanges and other fittings are wrought AlBrz
- Avoids cracking problems with welding SS fitting to AlBrz pipe
- Replacement valves are stainless steel
- Design changes for valves are in process; some will be replaced with cast AlBrz until stores are exhausted
- Zero-degree and Phased-array UT can detect and characterize dealloying under optimal conditions
- Continued development is ongoing but is not expected to be viable in near future 10 11/13/2013
AlBrz Dealloying Background (continued)
- Analytical models for evaluating structural integrity based on ASME Section XI and GL 90-05
- ASME Section XI Appendix H 1989
- Basic model assumes dealloyed flaw region (identified from through-wall leak) has zero strength or fracture toughness and uses conservative values for material properties
- During License Renewal, NRC challenged underlying basis for analytical model as limited test data was used to construct and validate analytical model
- Mechanical properties, dealloying flaw length correlation based on outside diameter flaw length, and other factors used in analytical model based on small sample size
- Only one dealloyed component was bend/pressure tested to validate model predictions 11 11/13/2013
Testing Protocols
- Analysis Confirmatory Test (ACT)
- Pressure Test (hydro)
- Bend Test
- Comparison of actual stress applied to the component compared to the critical bending stress predicted by the model
- Inspection of sample for chemistry, mechanical properties, microstructure, degree of dealloying, and/or cracking
- Profile Examination (PE)
- Sectioning of component to map dealloying progression
- Correlation of observed outside diameter (OD) flaw length with flaw length at mean radius of component
- Inspection of sample for chemistry, mechanical properties, microstructure, degree of dealloying, and/or cracking 12 11/13/2013
Testing Protocols (continued)
- NRC requested a total of 9 ACTs and 22 PEs to provide reasonable basis that aluminum bronze components could perform intended function during period of extended operation
- NRC recommended ACTs be 3 components each in 3 different sizes
- NRC recommended that a valid ACT would require a minimum level of dealloying degradation 13 11/13/2013
Testing Protocols (continued)
- STP identified 18 cast components for testing
- Only 3 of the 18 had been identified as leakers
- Remaining components were selected based on potential of finding dealloying in those locations (i.e. same component in different train had dealloyed previously, stagnant flow conditions, etc.) and accessibility
- Components were removed during ECW System drain-downs to minimize unavailability impact on system
- 2 components removed in 2012 and 4 removed in early 2013 were part of initial test scope
- PE and ACT have been or will be performed on all components 14 11/13/2013
Preliminary AlBrz Testing Results
- All results are considered Preliminary as Final QA verification has not been completed on reports
- Testing performed by Intertek (Aptech) and subcontractors under Appendix B program
- Aptech was heavily involved with AlBrz testing and analysis during plant start-up and through 1990s
- Aptech is highly experienced in material testing and ASME Section XI flaw evaluations 15 11/13/2013
2013 Testing Completed To Date
- ACT (bend test + hydro) and PE (sectioning and etching) completed on:
- 2 - 4 globe valves*
- 1 - 10 WN flange**
- 1 - 8 WN flange
- 2 - 3 WN flanges
- Through-wall leakers with no crack
- ** Through-wall leaker with crack
- Mechanical/chemical testing was not performed on every sample due to combinations of:
- Lack of dealloying
- Dealloyed area too small to fabricate test specimens
- Microstructure examination performed on selected components to ensure dealloying continues to propagate as bimetallic area 16 11/13/2013
Valve Bend Test 17 11/13/2013
Valve Bend Test Results Analysis Confirmatory Test for 4-inch Valves 0
10 20 30 40 50 60 70 80 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 TW Degradation Length, (inches)
Critical Bending Stress, (ksi)
Failure Line Bend Test Max Pipe Stress Leakage Length 4-Inch NPS D = 4.5" t = 0.237" Service Loading Condition Calculated Margin ASME Section XI Appendix H Required Margin (SF)
Level B (Upset) 54.2 2.77 Level D (Faulted) 44.2 1.39 18 Predicted bending stress to fail component Actual test bending stress Analytical Flaw Length 11/13/2013
Valve Pressure Test 19 11/13/2013
Valve Pressure Test Results Valve Initial Pressure (psi)
Hold Time (min)
Final Pressure (psi)
Visible Leakage EWFV-6936 100 5
100 No Leaks 151 5
151 No Leaks EWFV-6937 100 5
100 No Leaks 154 5
154 No Leaks Valve Initial Pressure (psi)
Hold Time (min)
Final Pressure (psi)
Visible Leakage EWFV-6936 500 1140 345 No Leak 500 5
500 No Leak EWFV-6937 500 1200 203 No Leak 500 180 487 No Leak Pneumatic Pressure Test Hydrostatic Pressure Test Note: Design Pressure = 120 PSI / Operating Pressure = 80 PSI Pressure Margin is approximately 4:1 20 11/13/2013
Flange Bend Test
~0.88 long crack placed in area of max tensile stress 10 flange undergoing bend test 21 11/13/2013
Flange Bend Test Stable crack tearing during failure. Failure initiated from original crack location Plug-like dealloying around crack location 22 11/13/2013
Flange Bend Test Results Notes:
- Model Dealloying Length is based on AES-C-1964-5 Fig. 4-1
- Actual TW Dealloying Length is based on examination of fracture surface at mid-wall 23 Service Loading Condition Calculated Margin ASME Section XI Appendix H Required Margin (SF)
Level B (Upset) 16.1 2.77 Level D (Faulted) 14.8 1.39 10-inch NPS D = 10.75 t = 0.365 11/13/2013
Flange Pressure Test Leakage at existing crack location during hydro of 10 flange 24 11/13/2013
Flange Pressure Test Results Note: Design Pressure = 120 PSI Pressure Margin is approximately 2.3:1 25 11/13/2013
ACT Testing Summary
- All tested components were able to support a bending stress greater than the predicted bending stress
- All components were able to hold a pressure without failure of at least 2x design pressure
- All components had substantial structural margins (structural capacity greatly exceeded ASME required Structural Factors)
- 3 of the 6 tested components had minimal dealloying but supported loads in excess of critical stress for pre-service components 26 11/13/2013
Profile Exam Results 27 11/13/2013
Profile Exam Results 28 11/13/2013
Profile Exam Results ID#
Description Max %
DA Avg %
DA Dealloying Character (Plug / Layer)
Crack (Y/N) 2c to 2d Correlation Valid?
F-261 3 150# FF WN Flange 21.0
~5%
Plug. Narrow, isolated dealloyed regions N
N/A F-169 3 150# FF WN Flange 39.2
~5%
Plug. Narrow, isolated dealloyed regions N
N/A F-059 8 150# FF WN Flange 22.0
~5%
Plug. Narrow, isolated dealloyed regions N
N/A F-064 10 150# FF WN Flange 100.0
~40%
Plug with more extensive dealloyed areas. Limited axial extent. One crack (~0.88 on OD, ~2.75 on ID)
Y Y
V-037 4 150# Globe Valve 100.0
~40%
Plug with more extensive dealloyed areas. On both inlet/outlet flanges and throughout valve body N
N/A V-041 4 150# Globe Valve 100.0
~40%
Plug with more extensive dealloyed areas. On both inlet/outlet flanges and throughout valve body N
N/A 11/13/2013 29 Notes:
DA = dealloying Avg % Dealloying is estimated, actual average not available yet Max % DA is a local maximum at varying circumferential cuts OD crack angle to through-wall dealloying angle (2c 2d) correlation is from Aptech AES-C-1964-5
Profile Exam Summary
- More extensive dealloying present on both valve bodies and 10 flange
- Dealloying is plug-like with through-wall leakage occurring before average dealloying % reaches ~60%
away from the through-wall flaw 30 11/13/2013
Mechanical Testing Completed To Date
- Tensile Test
- Yield (Sy) and Ultimate (Su) Strength
- Yield by 0.2% Offset (OS) and 0.5% Extension Under Load (EUL) methods
- Typically ductile materials are measured by 0.5% EUL
- Note some older tests did not calculate yield, only ultimate strength
- Crack Tip Opening Displacement (CTOD) Test
- Fracture Toughness (KCTOD or KIC)
- Specimens
- Mix of CA954/952 material, ~24 tensile and ~25 CTOD specimens
- Pump casing, 4 globe valve body, cast tees, small-bore fittings
- Flanges were wrong geometry/thickness to produce acceptable test specimens
- Specimens were all sub-size (but standard)
- Sub-sized specimens are more subject to casting flaws/voids that dont affect macroscopic properties of larger specimens
- True values for Sy, Su, and KCTOD for dealloyed material are likely higher than reported test values 31 11/13/2013
Mechanical Properties
- Pre-service Material Properties
- Specified Minimum Strengths
- Models conservatively use strength of CA-952 for analysis
- CMTR for as-fabricated material typically reports higher yield and ultimate strengths
- Fracture Toughness
- Not specified as part of material specification
- Previously determined from STP test data in 1980s to be in the range of 63.5 - 95.1 ksi in1/2
- Conservatively taken as 65 ksi in1/2 in analytical models 32 CA-952 CA-954 Sy (ksi) 25 30 Su (ksi) 65 75 11/13/2013
Test Specimens CTOD Specimen Tensile Specimen 33 11/13/2013
Tensile Test Results - Yield Strength 0.2% Offset Yield Strength Data for Al-Brz at Room Temperature 0
10 20 30 40 50 60 70 0
10 20 30 40 50 60 70 80 90 100 Percent Dealloying, %DA Yield Strength, Sy (ksi)
Small Bore Fittings (Bechtel 1988) (CA954) 8-inch Pump Shaft Casing Heat 24900 (CA954) 8-inch Pump Shaft Casing Heat 25838 (CA954) 4-inch Valve EWFV-6936 (CA954) 4-inch Valve EWFV-6937 CA954) 10x10x6 Tee Piece #3 (CA952) 10x10x6 Piece #4 (CA952) 10x10x4 Tee (CA952) 34 11/13/2013
Tensile Test Results - Yield Strength 0.5% EUL Yield Strength Data for Al-Brz at Room Temperature 0
10 20 30 40 50 60 70 80 0
10 20 30 40 50 60 70 80 90 100 Percent Dealloying, %DA Yield Strength, Sy (ksi) 8-inch Pump Shaft Casing Heat 24900 (CA954) 8-inch Pump Shaft Casing Heat 25838 (CA954) 4-inch Valve EWFV-6936 (CA954) 4-inch Valve EWFV-6937 (CA954) 10x10x6 Tee Piece #3 (CA952) 10x10x6 Tee Piece #4 (CA952) 10x10x4 Tee (CA952) 35 11/13/2013
Tensile Test Results - Ultimate Strength Ultimate Tensile Strength Data for Al-Brz Castings at Room Temperature 0
10 20 30 40 50 60 70 80 90 100 110 120 0
10 20 30 40 50 60 70 80 90 100 Percent Dealloying, %DA Ultimate Tensile Strength, Su (ksi)
Small Bore Fittings (Bechtel 1988) (CA954) 8-inch Pump Shaft Casing Heat 24900 (CA954) 8-inch Pump Shaft Casing Heat 25838 (CA954) 4-inch Valve EWFV-6936 (CA954) 4-inch Valve EWFV-6937 (CA954) 10x10x6 Tee Piece #3 (CA952) 10x10x6 Tee Piece #4 (CA952) 10x10x4 Tee (CA952) 36 11/13/2013
CTOD Test Results K-CTOD (Pmax Data) vs Percent Dealloying on Uncracked Section (Properties Adjusted for Specimen %DA) 0 10 20 30 40 50 60 70 80 90 100 110 120 0
10 20 30 40 50 60 70 80 90 100 Percent Dealloying, %DA Fracture Toughness, KCTOD, (ksi in1/2)
Small-Bore Valves (CA954) 8-inch Pipe Casing Heat 24900 (CA954) 8-inch Pipe Casing Heat 25838 (CA954) 4-inch EWFV6937 Inlet Flange (CA954) 10x10x6 Tee Piece #4 (CA952) 10x10x6 Tee Piece #11 (CA952) 10x10x4 Tee (CA952)
Regression Fit 37 11/13/2013
Mechanical Testing Summary
- Material retains strength and ductility in dealloyed state
- Ultimate strength asymptotically approaches ~30 ksi as %
dealloying increases
- Yield strength asymptotically approaches ~28 ksi as %
dealloying increases
- Material retains fracture toughness in dealloyed state
- Fracture toughness falls into the 25-30 ksi in1/2 as % dealloying approaches 100%
- Material retains ability to resist crack propagation
- Values for 100% dealloyed ultimate strength (30 ksi) and pre-service fracture toughness (65 ksi in1/2) are consistent with values used in previous analyses
- Samples with 20-25 years of aging have same properties as original samples given the same level of dealloying 38 11/13/2013
Chemical Testing/Micrography Results 11/13/2013 39
~4% Al
~11% Al
Chemical Testing/Micrography Results 11/13/2013 40
~0% Al
~9.5% Al
Chemical Testing/Micrography Summary
- Dealloyed regions are low in aluminum and undealloyed regions have aluminum content consistent with CMTR chemistry
- Reflects corrosion of high Al-content gamma-2 and/or beta phases in dealloyed regions
- Alpha phase grains are intact in both regions but have deposited Cu in dealloyed regions from corroded eutectoid
- Chemical testing and SEM examination validates use of visual methods (surface etching) for characterizing depth of dealloying as chemistry corresponds to visual indications 11/13/2013 41
Future Testing Plans
- STP intends to continue testing of AlBrz components in early 2014
- 11 components are currently planned for removal and testing between October 2013 and February 2014
- 3 - 4 WN flanges
- 4 - 6 WN flanges
- 1 - 6x6x6 tee
- 2 - 8 WN flanges
- 1 - 10 WN flange
- Components will be tested (ACT and PE) regardless of presence of leaks or % dealloying
- As opportunity presents, additional tensile and CTOD specimens will be selected for testing to build out material property curves 42 11/13/2013
Dealloying Program Procedure Development
- STP is in process of developing AlBrz Dealloying Management Program procedure
- Addresses Aging Management concerns by trending results of destructive testing and specifies destructive testing for future components
- Provides consistent, clear guidance on applying previously developed methods for structural integrity evaluations, operability reviews and relief requests
- Provides guidance on selecting NDE methods for examining dealloyed components
- Provides repository and reference for numerous reports, calculations and correspondence that support dealloying licensing basis
- Expected to be complete in early 2014 43 11/13/2013
Summary
- All testing completed to date indicates that analytical models for managing and dealloying are conservative
- Leak-before-break remains valid method for managing dealloying
- All components had substantial structural margins
- Material properties appear to only be affected by dealloying percentage, not component age
Questions?
45 11/13/2013