Post-Weld Heat Treatment on Dissimilar Metal Welds in the … Weld overlays Post Weld Heat Treatment...
Transcript of Post-Weld Heat Treatment on Dissimilar Metal Welds in the … Weld overlays Post Weld Heat Treatment...
Junseog Yang*, Ho-Sub Kim**, Changheui Jang**,
and Kyung Soo Lee*
*KHNP-CRI(Korea Hydro & Nuclear Power Co., LTD - Central Research Institute)
**KAIST(Korea Advanced Institute of Science and Technology)
Nuclear & High Temperature Materials Laboratory
Post-Weld Heat Treatment on Dissimilar Metal Welds in
the Primary Piping System of PWRs to Mitigate PWSCC
Susceptibility
1st KEPIC/ASME Joint Seminar 2017.09.04-05
Sep. 4th
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Contents
I. Introduction
II. Objective
III. Feasibility evaluation of PWHT application on DMW
Part I. Considerations for PWHT
Part II. Evaluation of PWHT effect on mechanical/corrosion properties of DMW
Part III. Evaluation of PWHT effect on PWSCC resistance of Ni-base weld
IV. Summary and further work
Introduction
PWR experience in dissimilar metal weld (DMW) Butt Welds : RPV and PZR nozzles
Weld residual stress and strain are the dominant mechanical driving force for
crack initiation and propagation within the DMW material due to PWSCC
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Units Welds Date Operating time
VC SUMMER RPV Outlet Nozzle 2000 16 years
RINGHALS 3 and 4 RPV Outlet Nozzle 2000 19 and 17 years
TIHANGE 2 RPV Outlet Nozzle 2003
20 years PZR Surge Nozzle 2002
CALVERT CLIFFS 2 Piping Drain Nozzle 2005 28 years
*2. R.W. Staehle, Cold-work workshop, 2007
*1. EPRI, MRP -220, Technical report, 2007
*1. EPRI, MRP-220, Technical report, 2007
Remedial methods for mitigation of PWSCC Environment
Zn additions
Optimization of hydrogen partial pressure
Temperature reduction
Material Replace components
Use more Cr containing materials
Stress Peening of various types
Water jet, shot, ultrasonic and laser
Mechanical stress improvement
Weld overlays
Post Weld Heat Treatment
Introduction
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Material Composition
Heat treatment
Microstructure
Surface condition
Environment Composition
Temperature
Corrosion potential
Flow rate
Stress / Strain Service stresses
Fit-up stresses
Residual stresses
Strain rate
SCC
Fatigue Corrosion
fatigue
Corrosion
*4. P.L. Andresen, Cold-work workshop, 2007
*3. P. Scott, INL Seminar on SCC in LWRs, 2013
Introduction
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Limitations Needed to optimize PWHT*8
Limited temperature for application Up to < 650oC due to temper embrittlement of low alloy steels
→ Need to evaluate mechanical properties after PWHT A concern for sensitization of stainless steels
Similar temperature range : 500oC - 800oC
Cold Work enhanced sensitization kinetics*9
→ Need to evaluate sensitization behavior of SSs after PWHT
PWHT on DMW
Beneficial effects Reduce residual stress
Relaxation of residual strain
Relaxation of surface Cold Work
Grain boundary carbide precipitation
→ Improvement of PWSCC resistance of DMW*5,6,7
*5. S.L. Hong, et al, 10th EDM, 2001
*6. T.Cassagne, et al, 9th EDM, 1999
*7. C. Guerre, 15th EDM, 2011
*8. G. White, MRP-115, EPRI, 2004
*9. R. Singh, et. al., Corrosion, 61, 907, 2005
.
Objective
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Alloy 182 PWSCC
resistance properties
(initiation / CGR)
Evaluation of
PWHT effect on
mechanical/corrosion
properties of DMW
PWHT effect on
PWSCC resistance
of Ni-base weld
Feasibility evaluation
of PWHT application
on DMW
Mechanical
properties
PWHT effect on dissimilar metal weld
Corrosion
properties
Ni-base weld metal
PWSCC resistance
evaluation
Development of technical regulation for PWHT
Creep properties
PWHT condition
determination
Research on considerations
for PWHT condition
Sensitization evaluation
depending on PWHT
Creep properties of Alloy
182 depending on PWHT
Tensile properties,
micro-hardness
Considerations
for PWHT
Part. I
Part. II
Part. III
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Feasibility evaluation of PWHT application on DMW
Part I. Considerations for PWHT
Considerations for PWHT
Sensitization of stainless steel Temperature occurring sensitization of stainless steels : 500-850oC
Depletion of Cr in the vicinity of Cr23C6 precipitation
L-grade SSs are resistant to sensitization due to low C content
0~5% residual ferrite contained in general
Effect of residual ferrite on sensitization of L-grade of SSs has not been well understood
US NRC Reg. guide 1.44 (Control of the processing and use of stainless steel) Material subjected to sensitizing temperature in the range of 427 to 816 oC should be L-grade
material (less than 0.03 wt% C)
Exceptions : Material exposed to PWR coolant with controlled dissolved oxygen
concentration during normal operation
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*10. H. Sidhom, Metall. And Mater. Trans. 38A, 1269, 2007
*10TTP diagram of 316L SSs: non-CWed
Considerations for PWHT
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IG carbide precipitation for PWSCC resistance of Ni-base weld Beneficial effect on CGR : decrease after PWHT
Improvement of initiation resistance after PWHT
NbC, Cr-rich (Cr23C6) carbide precipitation on GB
CEA, Alloy 82, 600oC*7h*12
PWHT
IG carbide NbC
Cr23C6
EDF, Alloy 182, 610oC*6h*13
PWHT
*11 P. Scott et al, MRP-215, EPRI, 2007 *12. C. Guerre, 15th EDM, 2011 *13. S.L. Hong, et al, 10th EDM, 2001
MRP-215, AREVA-NP, Alloy 82/182*11
Stress relief
(610oC*10h)
No
stress relief
(a)
(b)
U-bend test
PWSCC growth rate PWSCC initiation
Considerations for PWHT
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IG carbide precipitation for PWSCC resistance of Ni-base weld Effect of carbon content (Alloy 182, 610oC*6h)*14
Low carbon content (< 0.03 wt%) – GBC increased
High carbon content (> 0.08 wt%) – No GBC change
Effect of ratio and size of GBC on CGR is in question
Temper embrittlement of low alloy steel Temperature for PWHT is limited below 700oC
Weld %C GBC(%) %GB carbides
size>1μm
D545 AR .029 28 3
D545 SR .029 38 .5
M1 AR .022 26 4
M1 SR .022 44 3
M2 AR .081 48 13.5
M2 SR .081 43 13
M4 AR .089 65 10
M4 SR .089 65 5
*14. T.Cassagne, et al, 9th EDM, 1999
PWHT condition should be determined to improve
PWSCC resistance while avoiding sensitization and
temper embrittlement
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Feasibility evaluation of PWHT application on DMW
Part II. Evaluation of PWHT effect on
mechanical/corrosion properties of DMW
Test material and condition Dissimilar Metal Weld (DMW)
SA508 Gr.1a
Alloy 82/182
F316L & F316 stainless steel
PWHT Condition
10hours holding at 600oC, 650oC, 700oC
Heating rate : 38oC/h above 350oC
Furnace cooling
Determined from NESC-III project*15
Experimental
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F316L or F316
Alloy 182
SA508 Gr.1a Alloy 82
Dissimilar Metal Weld
Materials C Mn P Si Ni Fe Cr Mo Nb
+Ta
F316L SS
(F316)
0.02
(0.05) 1.29 0.15 0.55 11.0 Bal. 16.7 2.59 -
Alloy 182 0.056 6.60 0.006 0.335 Bal. 3.25 14.06 0.008 1.50
SA508
Gr.1a 0.24 1.24 .009 0.25 0.29 Bal. 0.19 0.06 -
*15. N. Taylor et. al., NESC-III project, 2006
Experimental
Mechanical tensile test ASTM E8/E8M-13a
Standard test methods for tension testing of metallic materials
Round bar type Gauge length 24mm, dia. 4mm
Strain rate 5×10-4/s
Test condition : RT air
Strain measured by extensometer (epsilon 3555)
Creep test ASTM E139-11
Standard test method for conducting creep, creep-rupture, and stress-rupture test of metallic
materials)
Test condition 600, 650, 700oC air
Primary creep behavior focused Tested during 30-48 hrs
Test load 150, 220, 270 MPa
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PWHT effect on mechanical properties
Mechanical properties of DMW after PWHT Stainless steel (F316, F316L)
Yield strength decreased (max. 30MPa)
Changes of tensile strength and elongation are not
significant
SA508 Gr.1a No elongation change
Significant changes on tensile strength above
650oC due to tempering effect
Alloy 182 Yield strength decreased and tensile strength
increased above 650oC
No elongation change
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316 SS 316L SS SA 508 Alloy 1820
100
200
300
400
500Test temperature: RT
As-received PWHT (600 oC)
PWHT (650 oC) PWHT (700
oC)
Yie
ld s
trength
(M
Pa)
316 SS 316L SS SA 508 Alloy 182400
450
500
550
600
650
700Test temperature: RT
Tensile
str
ength
(M
Pa)
As-received PWHT (600 oC)
PWHT (650 oC) PWHT (700
oC)
316 SS 316L SS SA 508 Alloy 18220
40
60
80
100Test temperature: RT
Elo
ngation (
%)
As-received PWHT (600 oC)
PWHT (650 oC) PWHT (700
oC)
100
150
200
250
300
700oC650
oC600
oCAR
Mic
ro-h
ard
ness (
HV
0.1
)
316 SS 316L SS
SA 508 Alloy 182
tempering effect
Micro-hardness
PWHT effect on mechanical properties
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Creep properties of Alloy 182 Concerns for deformation by creep due to self-load during PWHT
Creep strain depending on load and temperature
0 5 10 15 20 25 300.0
0.2
0.4
0.6
0.8Test condition: 600
oC, air
Alloy 182, 150 MPa
Alloy 182, 220 MPa
Alloy 182, 270 MPa
Cre
ep
str
ain
(%
)
Time (hr)0 5 10 15 20 25 30
0
5
10
15
20
25Test condition: 650
oC, air
Alloy 182, 150 MPa
Alloy 182, 220 MPa
Alloy 182, 260 MPa
Time (hr)
Cre
ep s
train
(%
)
0 5 10 15 20 25 300
5
10
15
20
25Test condition: 700
oC, air
Alloy 182, 150 MPa
Alloy 182, 220 MPa
Alloy 182, 250 MPa
Time (hr)C
reep s
train
(%
)
600oC 0.265% creep strain during 10hrs under 270MPa
(lower compared to 650, 700oC)
650, 700oC Creep strain rise sharply at 260, 250Mpa (near yield
stress) loads
Estimated deformation 600oC : 0.065~0.265% strain (10hr HT time)
650oC : 0.138~18.6% strain (10hr HT time)
700oC : 0.835~30.4% strain (1.5hr, 3.5hr HT time)
PWHT effect on microstructure
Microstructure characteristics after PWHT F316 SS
Grain boundary carbide (Cr-rich M23C6) precipitation
F316L SS No grain boundary precipitates due to low carbon content (0.03 wt%)
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PWHT effect on microstructure
Microstructure characteristics after PWHT SA508 Gr.1a
Ferrite with pearlite microstructure for all condition
Alloy 182 Columnar dendritic structure
Cr-rich carbide and NbC precipitation after PWHT
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Experimental
Sensitization test ASTM A262 practice A (Oxalic acid etching test)
Standard practices for detecting susceptibility to intergranular attack in stainless steel
ASTM G108 (DL-EPR) Standard test method for double loop electrochemical potentiokinetic reactivation test for
detecting sensitization of stainless steels
Degree of Sensitization (DOS) : Ir / Ia ×100 Ir : Reactivation current peak
Ia : Activation current peak
In typical 316L SS
Acceptable less than 0.2*16
Significant sensitization with greater than 7*17
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Solution 0.5 M H2SO4 + 0.01 M KSCN
Starting voltage 50 mV below open circuit potential (OCP)
Scan rate 1.67 mV/s
Vertex potential 700 mV ▲ Diagram for the procedures of double loop EPR test method
*16. G.H.Aydogdu, Corr. Sci. 48, 3565, 2006
*17. T.K.Yeh et al., 15th EDM, 2011
PWHT effect on sensitization
Oxalic acid etching test (ASTM A262 practice A) F316L SS : No sensitization under PWHT cond.
F316 SS : Not significant until 10hrs at 600, 650oC
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HT 0 h 5 h 10 h 30 h 50 h 100 h
F316L SS
(650oC)
Step
structure
Step
structure
Step
Structure
Dual
Structure
Dual
Structure -
F316L SS
(700oC), SA
Step
structure
Step
structure
Step
structure
Dual
structure
Ditch
Structure
Ditch
Structure
Sensitized
Step structure
Dual structure
Ditch structure
HT 1.5h 5h 10h 20h 30h 50h 100h
F316 SS
(550oC)
Step
structure
Step
structure
Step
structure
Step
structure
Step
structure
Step
structure
Step
structure
F316 SS
(600oC)
Step
structure
Step
structure
Step
structure
Dual
structure
Dual
Structure
Ditch
Structure
Ditch
Structure
F316 SS
(650oC)
Step
structure
Step
structure
Step
structure
Dual
structure
Ditch
Structure
Ditch
Structure
Ditch
Structure
PWHT effect on sensitization
DL-EPR test (ASTM G108) F316L stainless steel
No sensitization under PWHT condition
F316 stainless steel (0.05 wt% C) Sensitization could be accelerated due to higher carbon content than F316L SS
No sensitization until 100hrs at 550oC
Not significant until 10hrs at 600, 650oC
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TTS diagram of 316 SS*18 (C: 0.066 wt%)
*18. B. Weiss, et al., Metallurgical Transactions, 851-866, 1972
PWHT
condition
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Feasibility evaluation of PWHT application on DMW
Part III. Evaluation of PWHT effect on PWSCC
resistance of Ni-base weld in DMW
Experimental
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PWSCC test for Alloy 182 PWSCC Initiation test
Using spring-loaded U-bend specimen (t=3mm) (ASTM G30) Standard practice for making and using U-bend stress-corrosion test specimens
Pre-formed to 3% => Flattening
=> bending them to 11.3% in the reverse direction
13.0%
Sample machined L-S orientation
As-welded / 600oC*10h condition
Crack observation
Exposure time
100, 500, 800, 1000h
*19. EPRI, MRP-215, Technical report, 2007
Test system Water loop to simulate PWR environment
Recirculation system
2 Autoclave in parallel
Experimental
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Test time 1000 hours
Water temperature & pressure 325oC, 15.5MPa
Water
Chemistry
pH 6.3 at room temperature
DO < 5 ppb
DH 2.2 ppm (30 cc/kg)
Conductivity ≈ 22 S/cm (pure water + 1200 ppm H3BO3 + 2.2 ppm LiOH)
PWSCC initiation test Applied 13% strain
130% yield stress from Alloy 182 stress-strain behavior
Cracking behavior As-welded condition
All specimen cracked at 1000h
PWHT (600oC, 10h) condition
GB carbide observed
Improved SCC initiation resistance until 500hr
Cracking tendency increased after 500hr
Additional test needed 620, 650oC condition – under test
PWHT effect on PWSCC resistance
Alloy 182
PWSCC
initiation
time
As-welded
(pre-strained)
PWHTed
(pre-strained)
PWHTed
(single bent)
Cracked specimen ratio
100h 4/20 2/10 0/10
500h 11/20 3/10 2/10
805h 17/20 8/10 7/10
1000h 20/20 9/10 8/10
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Summary and further work
Summary Mechanical properties
No significant changes at 600oC*10h condition
Mechanical property changes for 182, SA508 above 650oC
Sensitization Not sensitized for F316 SS(0.05 wt% C) at 600oC*10h condition
No sensitization for F316L SS under all PWHT conditions
PWSCC Improved initiation resistance for Alloy 182 (600oC*10h)
Higher temperature condition (620, 650oC) test needed for detail
analysis
Further work PWSCC growth rate test to confirm previous research results
Application to Mock-up nozzle and properties evaluation
Development of technical regulation for PWHT
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