Welding and Repair Technology Center

Alloy 52/52M Welding Issues

Steve McCracken
Sr. Project Manager
EPRI Welding & Repair Technology Center

NRC/Industry Meeting
Rockville, Maryland
May 26, 2010
 Presentation Roadmap

• Industry issue – Weld Metal 182 PWSCC

• Mitigation and Repair Options

• Mitigation ASME Code Cases

• Weld Metal 52/52M Challenges and Weldability Issues

• Welding & Repair Technology Center (WRTC)

Weldability Testing and Activities

© 2010 Electric Power Research Institute, Inc. All rights reserved. 2 Welding and Repair Technology Center
 Nuclear Power Industry Issue

• INCONEL 182 (ENiCrFe-3)

filler metal was used
extensively in dissimilar metal
welds for critical reactor coolant
system components
• Over time 182 is degraded by
primary water stress corrosion
cracking (PWSCC)
• Filler metal 52M (ERNiCrFe-
7A) with ~30wt% Cr has high
resistant to PWSCC and is
currently filler metal used for
mitigation, repair, and new
fabrication
Westinghouse 4-Loop PWR

© 2010 Electric Power Research Institute, Inc. All rights reserved. 3 Welding and Repair Technology Center
 Presentation Roadmap

• Industry issue – Weld Metal 182 PWSCC

• Mitigation and Repair Options

• Mitigation ASME Code Cases

• Weld Metal 52/52M Challenges and Weldability Issues

• Welding & Repair Technology Center (WRTC)

Weldability Testing and Activities

© 2010 Electric Power Research Institute, Inc. All rights reserved. 4 Welding and Repair Technology Center
 82/182 PWSCC Mitigation and Repair

• Weld Overlay
– Full structural or optimized 52M weld
overlay is industry accepted method
for repair or mitigation of PWSCC
susceptible 82/182 welds

In-process 52M Overlay on

Pressurizer Safety Nozzle

Schematic of 52M Structural Weld Overlay

© 2010 Electric Power Research Institute, Inc. All rights reserved. 5 Welding and Repair Technology Center
 82/182 PWSCC Mitigation and Repair

• Inlay / Onlay on Inside Diameter

– 52M provides barrier between susceptible 182 and environment
– Machine GTAW or underwater laser beam welding process

Schematic of 52M
Inlay & Onlay Mitigation

© 2010 Electric Power Research Institute, Inc. All rights reserved. 6 Welding and Repair Technology Center
 82/182 PWSCC Mitigation and Repair

• Excavate & Weld Repair

Schematic of 52M Excavate & Weld Repair

© 2010 Electric Power Research Institute, Inc. All rights reserved. 7 Welding and Repair Technology Center
 Presentation Roadmap

• Industry issue – Weld Metal 182 PWSCC

• Mitigation and Repair Options

• Mitigation ASME Code Cases

• Weld Metal 52/52M Challenges and Weldability Issues

• Welding & Repair Technology Center (WRTC)

Weldability Testing and Activities

© 2010 Electric Power Research Institute, Inc. All rights reserved. 8 Welding and Repair Technology Center
 ASME Code & Regulatory Documents

• NRC Regulatory Documents

– Regulatory Guide 1.147
– Site specific relief requests
• NRC Accepted ASME Documents (revision in parenthesis
indicates update currently in ASME XI Standards committee)
– N-638-1
N 638 1 (6) RG 11.147
14 conditions,
diti Si il and
Similar d Di
Dissimilar
i il M Metall
Welding Using Ambient Temperature Machine GTAW Temper
Bead Technique
– N-504-3 (4) RG 1.147 conditions, Alternative Rules for Repair of
Classes 1, 2, and 3 Austenitic Stainless Steel Piping
– Nonmandatory Appendix Q, Weld Overlay Repair of Class 1, 2,
and 3 Austenitic Stainless Steel Piping Weldment

© 2010 Electric Power Research Institute, Inc. All rights reserved. 9 Welding and Repair Technology Center
 ASME Code & Regulatory Documents

• New ASME Code Cases (not yet in RG 1.147 and/or still in

ASME committee)
– N-740-3, Dissimilar Metal Weld Overlay Repair for Class 1, 2, and
3 Items
– N-754, Optimized Structural Dissimilar Metal Weld Overlay for
Mitigation
g of PWR Class 1, 2, and 3 Items
– N-766, Nickel Alloy Reactor Coolant Inlay and Onlay for
Mitigation of PWR Full Penetration Circumferential Nickel Alloy
Welds in Class 1 Items
– N-XXX, Similar and Dissimilar Metal Welding Using Ambient
Temperature Automatic or Machine Dry Underwater Laser Beam
Welding (ULBW) Temper Bead Technique
• New Excavate Weld and Repair (EWR) Initiative

© 2010 Electric Power Research Institute, Inc. All rights reserved. 10 Welding and Repair Technology Center
 Presentation Roadmap

• Industry issue – Weld Metal 182 PWSCC

• Mitigation and Repair Options

• Mitigation ASME Code Cases

• Weld Metal 52/52M Challenges and Weldability Issues

• Welding & Repair Technology Center (WRTC)

Weldability Testing and Activities

© 2010 Electric Power Research Institute, Inc. All rights reserved. 11 Welding and Repair Technology Center
 Alloy 52 & 52M Welding Challenges

• Alloy 52 / 52M weldability

issues
– Sluggish weld puddle
– High welder skill required
– Heat-to-heat composition
variations can result in significant
difference in weldability
• Ti & Al oxide buildup
• Tendency for lack of bond and/or lack of fusion
• Susceptible to various types of weld metal cracking
– Ductility dip cracking (DDC)
– Liquation cracking
– Solidification cracking

© 2010 Electric Power Research Institute, Inc. All rights reserved. 12 Welding and Repair Technology Center
 Alloy 52 Overlay Weldability Issues

• High welder skill required

– Proficiency training is a necessity
– Classroom training recommended to
ensure understanding of weld process
limitations
• Weld process parameters
– Demonstration necessary with process limitations clearly defined
– Important weld process parameters
• Power ratio versus heat input
• Double up versus orbital
• Pulse versus steady current
• Tungsten travel speed & wire feed rate

© 2010 Electric Power Research Institute, Inc. All rights reserved. 13 Welding and Repair Technology Center
 Alloy 52 Ti & Al Oxide Issues

• Ti & Al oxides buildup

with multipass welding
• Intermittent oxides are
trapped and align to
create rejectable UT
indication
• New Alloy 52M
formulation (less Ti &
Al) has reduced
tendency for oxide
buildup

© 2010 Electric Power Research Institute, Inc. All rights reserved. 14 Welding and Repair Technology Center
 Lack of Bond (LOB) & Lack of Fusion (LOF)

• LOB & LOF most likely with low heat

input GTAW (>24% Cr on first layer)
• Solution
– Increase power ratio
(higher heat input)
– Optimized
O ti i d process &
technique controls
• Double up progression,
steady current, slight
oscillation
• Orbital progression, pulse current
• Tungsten angle, bead overlap

© 2010 Electric Power Research Institute, Inc. All rights reserved. 15 Welding and Repair Technology Center
 Alloy 52M Ductility-Dip & Liquation Cracking

• Ductility-Dip Cracking (DDC)

– Subsurface solid state cracking
phenomenon in reheated Alloy 52
weld metal
– Occurs with ductility drop at high
temperatures
p concurrent with local
cooling strains
• Liquation Cracking
– Occurs in reheated Alloy 52 due to
low melting point constituents
• DDC & liquation cracking controlled
by weld metal chemistry and by
minimizing restraint

© 2010 Electric Power Research Institute, Inc. All rights reserved. 16 Welding and Repair Technology Center
 52M Hot Cracking on Stainless Base Materials

• Occurs when weld puddle

solidifies – typically detected by
PT examination
• Probable cause is high sulfur
(S) and phosphorus (P) in weld
puddle
• Testing
T ti indicates
i di t th thatt base
b
materials with S > 0.014 wt%
cause hot cracking
– Degree of susceptibility
depends on dilution
• Sources of high P & S
– Stainless steel safe-end
– Piping base materials
– Pipe-to-safe end weld metal

© 2010 Electric Power Research Institute, Inc. All rights reserved. 17 Welding and Repair Technology Center
 52M Hot Cracking on Stainless Cladding & Weld Metal

• 52M hot cracking occurs

when welding on flux
shielded weld metals
– Stainless steel SAW clad
– Stainless SMAW weld
metal
• Caused by trace impurities
in SAW and SMAW metal

CRDM Schematic with 52M Onlay

© 2010 Electric Power Research Institute, Inc. All rights reserved. 18 Welding and Repair Technology Center
 Solution(s) to Prevent Hot Cracking

• Decrease and control dilution:

– Decrease power ratio (heat input) to lower
dilution of base metal S & P into 52M weld metal
– Optimize and manage weld process parameters
– Install hot crack resistant stainless steel ER308L or
ER309L buffer (barrier) layer
• More than one buffer layer may be necessary

© 2010 Electric Power Research Institute, Inc. All rights reserved. 19 Welding and Repair Technology Center
 52M Hot Cracking on Cast Stainless Steel Piping

Test Mockup (below) - 52M pad

on ER308L buffer layer
Base metal is SA-351 CF8A
0.019% S, 0.032% P, 0.72% Si

• SEM of hot crack (above) in boat

sample removed from 52M overlay
• 52M layer (right) shows multiple
liquid penetrant crack indications

© 2010 Electric Power Research Institute, Inc. All rights reserved. 20 Welding and Repair Technology Center
 Influence of CASS Piping on 52M Weld Bead

• Influence of CASS trace

elements on weldability:
– Weld bead shape and
penetration
– Susceptibility
y to hot cracking
g Weld Shape on 304L Plate
• Industry needs to:
– Understand how CASS
influences 52M welding
– Identify deleterious trace
elements in CASS
– Define threshold values to
protect against hot cracking Weld Shape on CF8A (CASS) Pipe

© 2010 Electric Power Research Institute, Inc. All rights reserved. 21 Welding and Repair Technology Center
 Effect of Sulfur and Silicon on Austenitic Welds

From Tinkler – London Conf Nov 1983

• Sulfur influences the weld pool
surface tension gradient in
austenitic welds
• Surface tension gradient drives
molten metal flow (Marangoni
flow)
• Silicon addition decreases
viscosity which enhances flow
• Shallow & wide bead
< 0.008% sulfur
• Deep & narrow bead
> 0.015% sulfur
• High sulfur is known
to cause hot cracking

© 2010 Electric Power Research Institute, Inc. All rights reserved. 22 Welding and Repair Technology Center
 Sulfur Influence on Inconel 718 Weld Bead

• Sulfur increase from 0.0032 to

0.016wt% caused:
– 46% depth/width ratio increase
– 18% weld volume increase
– 32% penetration (depth) increase
• Influence attributed to classical
Marangoni mechanism
• Base metal melting efficiency
increased by moving warmer weld
metal to center of the pool –
dilution of weld metal increased From Walsh – TWR June 1998

© 2010 Electric Power Research Institute, Inc. All rights reserved. 23 Welding and Repair Technology Center
 Cause of Unexpected Hot Cracking on CASS

• Scenario:
– Machine GTAW procedure successfully developed and
demonstrated on stainless steel with low S & low Si
• Dilution and bead profile are controlled, well established, and
understood
– Field deployment of welding procedure and system
using identical process parameters on CASS or vintage
forging may vary
• Dilution and bead profile may be significantly different due to
base metal composition
• Unexpectedly high dilution can lead to hot cracking
– High S, Si, or S+P dilution in weld bead
– Fe dilution ≥35% (52M with 2.5% Nb may hot crack)
• Need better understanding on how minor element effect dilution

© 2010 Electric Power Research Institute, Inc. All rights reserved. 24 Welding and Repair Technology Center
 Presentation Roadmap

• Industry issue – Weld Metal 182 PWSCC

• Mitigation and Repair Options

• Mitigation ASME Code Cases

• Weld Metal 52/52M Challenges and Weldability Issues

• Welding & Repair Technology Center (WRTC)

Weldability Testing and Activities

© 2010 Electric Power Research Institute, Inc. All rights reserved. 25 Welding and Repair Technology Center
 52/52M Experience and New Compositions

• 52 prone to Ti & Al oxide buildup with multi-pass welding

• 52M developed to reduce oxide buildup
• 52 & 52M susceptible to DDC under high restraint conditions
• 52M is susceptible to hot cracking on high S & P base
materials
• 52M may be susceptible to hot cracking on flux shielded weld
metals (SAW clad and SMAW welds)
• 52M may be susceptible to hot cracking on cast stainless steel
piping
• 52MSS & 52i developed to improve resistance to DDC

© 2010 Electric Power Research Institute, Inc. All rights reserved. 26 Welding and Repair Technology Center
 EPRI Project - 52 Testing & Evaluation

• Standardize method for evaluating / measuring crack

susceptibility of high chromium nickel-base weld filler
metals
– Strain-to-fracture
– Transvarestraint
– Cast pin tear
Cast-pin-tear
– Thermal simulation (JMatPro / ThermoCalc)
– SS DTA (single sensor differential thermal analysis)
• Build matrix of Alloy 52 heats of various compositions with
crack susceptibility index number based on resistance to:
– Solidification (hot) cracking, and
– ductility-dip cracking

© 2010 Electric Power Research Institute, Inc. All rights reserved. 27 Welding and Repair Technology Center
 Alloy 52 Heats / Classifications in Test Matrix

• KAPL Alloys
– 27% Cr (MLTS-27) *
– 27% Cr (EN52i) ** (large production melt)
• Special Metals Inc. Alloys
– 52M ((ERNiCrFe-7A)) *
– 52MSS (ERNiCrFe-13) * (two small experimental melts)
– 52MSS (ERNiCrFe-13) * (large production melt)
– 82 ** (special heat with high resistance to hot cracking)

* Testing complete ** Testing in progress

© 2010 Electric Power Research Institute, Inc. All rights reserved. 28 Welding and Repair Technology Center
 Strain-to-Fracture (DDC Resistance) Test Results

14

14
• Strain-to-
12
Strain-to-Fracture Test Fracture test
Results at 950°C
ranking
10
– 52 and 52M
are equally
Applied strain (%)

>100 >100
8
0 31 >60 14 susceptible to
32 2 DDC
6
0 4
2
19 14 3
1 5 8 – 52MSS is
4
2 8 0
very resistant
0
7 5
2 0 and nearly
2 1 0 0 0
equal to 304L
0 0
0 SS
0
FM52 FM52M-A FM52M-B FM52X-D FM52X-H San-69HP FM82-A FM82-B

2.5Nb, 4Mo (52MSS)

© 2010 Electric Power Research Institute, Inc. All rights reserved. 29 Welding and Repair Technology Center
 Transverse Varestraint Testing

• The following classifications

are in program
– 1 heat 52M (ERNiCrFe-7A)
– 3 heats 52MSS (ERNiCrFe-13)
– 1 heat MLTS-27
– 1 heat EN52i
– 1 heat 82
• Alloy 600 plate used to
minimize effect of dilution
• EN52i & 82 testing in progress
¼” x 9” x 15” Specimen
with 3 Alloy 52 welds

© 2010 Electric Power Research Institute, Inc. All rights reserved. 30 Welding and Repair Technology Center
 Transverse Varestraint Test Specimen & Setup

• Transverse varestraint
weld bead
• Upward force to bend
specimen occurs during
welding to apply
augmented strain as weld
solidifies
lidifi
• Tested over range of
augmented strain values
(radius of die block
determines strain)

⎛ T ⎞
% Strain = ⎜ ⎟100
⎝ 2R ⎠

© 2010 Electric Power Research Institute, Inc. All rights reserved. 31 Welding and Repair Technology Center
 Transverse Varestraint Data
Maximum Crack Distance vs Augmented Strain

1.8
D5-8423 52MSS-A
1.6
HV1224 52MSS -B

susceptibility
higher crack
Maximum Crack Distance, mm

1.4

susceptibility
Polymet HD52 (MLTS-2)

gher crack
NXOT85 TK 52M
1.2

1.0

hig
0.8

0.6

0.4

0.2

0.0
0 1 2 3 4 5 6
Augmented Strain, %

© 2010 Electric Power Research Institute, Inc. All rights reserved. 32 Welding and Repair Technology Center
 Cast Pin Tear Test (CPTT)

• CPTT evaluates solidification and liquation crack

susceptibility
• Alloy charge is cast into a 3/8” diameter mold
• Charge may be adjusted for weld metal dilution
• Longitudinal tensile strain occurs in pin as it
solidifies and cools
• Strain increases as pin length increases
OSU castt pin
i tear
t test
t t apparatus
t

Set of buttons is Button is melted 3/8” diameter pins are cast from 3/8” to 2-1/8”
prepared for by electric arc gauge length in 3/8” increments. Head and foot
each heat and cast into of pin restrain gauge length during cooling
pin mold

© 2010 Electric Power Research Institute, Inc. All rights reserved. 33 Welding and Repair Technology Center
 Cast Pin Tear Data
Maximum Circumferential Crack vs Pin Length

Maximum Circumferential Cracking (MCC) Response Curves

100.0
52MSS-A (D58423)
Maximum Circumferenttial Cracking , %

90.0
52MSS-B (HV1224)
80.0 MLTS-2 (HD52)
52M (NX0T85TK)
70.0

60.0

50.0

40.0 higher crack lower crack

30.0
susceptibility susceptibility

20.0

10.0

0.0
0.250 0.500 0.750 1.000 1.250 1.500 1.750 2.000

Pin Length, in

© 2010 Electric Power Research Institute, Inc. All rights reserved. 34 Welding and Repair Technology Center
 Single Sensor Differential Thermal Analysis (SS DTA)
Introduction
Procedure

SS DTA Procedure Replicates GTA Weld Microstructure

• Epitaxial growth
• Columnar dendritic microstructure
• Interdendritic precipitation
• Dendrite arm spacing

1g Test
Button

20g Base
Button
52MSS-A SS DTA Button Sample 52MSS-A Transvarestraint Sample

© 2010 Electric Power Research Institute, Inc. All rights reserved. 35 Welding and Repair Technology Center
 Introduction
SS DTA Summary of Solidification Behavior

52MSS-A 52MSS-B MLTS-2 52M

Eutectic Range, oC 132 113 174 not detected
Solidification Range, oC 192 192 232 144

© 2010 Electric Power Research Institute, Inc. All rights reserved. 36 Welding and Repair Technology Center
 Comparison of Crack Susceptibility

• Solidification temperature range evaluation results

SS DTA (single sensor differential thermal analysis)

MLTS 27 (232 ºC)

MLTS-27 C) > 52MSS
52MSS-B
B (206 ºC)
C) > 52MSS
52MSS-A
A
(192 ºC) > 52M (144 ºC)

ThermoCalc / JMatPro calculations

MLTS-27 (231 ºC) > 52MSS-B (272 ºC) > 52MSS-A

(267 ºC) > 52M (145 ºC)

© 2010 Electric Power Research Institute, Inc. All rights reserved. 37 Welding and Repair Technology Center
 Comparison of Crack Susceptibility

• CPTT (cast pin tear test) results (hot cracking)

52MSS-A > 52MSS-B > MLTS-27 > 52M

• Transverse varestraint results (hot cracking)

52MSS-A > 52MSS-B > MLTS-27 > 52M

• Strain-to-Fracture Test Results (DDC)

52 = 52M > 52MSS

© 2010 Electric Power Research Institute, Inc. All rights reserved. 38 Welding and Repair Technology Center
 New Project – Evaluate Influence of CASS on 52M

• Evaluate Influence of Minor Alloying Elements in Cast

Stainless Steel on 52M Weldability
– Investigate range of CASS compositions
– CASS composition and trace element maximums will kept inside
specification limits for CF8A and CF8M
– Emphasis will be on influence of Sulfur and Silicon
– Welding process parameters will be consistent and set to typical
industry standard
– Single heat of nickel filler metal will be used to eliminate influence
of weld metal on bead shape

© 2010 Electric Power Research Institute, Inc. All rights reserved. 39 Welding and Repair Technology Center
 Weld Testing on CASS Samples

• Weld testing on nine

composition controlled
samples
– low S – low Si through
range of high S – high Si
– Determine hot cracking
threshold
– Evaluate influence of S &
Si synergy on weld bead
shape and dilution
– Repeat testing on select
archive CASS sample
materials for comparison

© 2010 Electric Power Research Institute, Inc. All rights reserved. 40 Welding and Repair Technology Center
 EPRI Project – Evaluate Influence of CASS on 52M

• Cast pin tear test (CPTT) of 52M diluted by ER308L-Si

filler wire
– CPTT developed at OSU to measure hot cracking threshold of
nickel weld metals
– ER308LSi wire used to dilute 52M pin button melts to simulate
stainless steel buffer layer
y
– FeS powder added to vary sulfur composition in pins
– Button melts for cast pins will simulate eight dilution ranges from 0
to 70% (52M diluted by ER308LSi and FeS)
– Computational analysis (ThermoCalcTM) and SS-DTATM will also
be used to determine thresholds for deleterious trace elements

© 2010 Electric Power Research Institute, Inc. All rights reserved. 41 Welding and Repair Technology Center
 Thank You – Questions or Comments?

Welding and Repair Technology Center

Together…Shaping the Future of Electricity

© 2010 Electric Power Research Institute, Inc. All rights reserved. 42 Welding and Repair Technology Center