Chloride-Induced Stress
Corrosion Cracking of
Austenitic Stainless Steel
David Spencer
3rd Year PhD Student
Nuclear Department
Area of Concern
Submarine PWR Primary Circuit
• Austenitic Stainless Steel – 304L
• Chloride Ions
– Cl-
• Tensile Stress – Applied or Residual
Crack Propagation
Transgranular
Crack
propagating
across grains
Grains
Metallic
Grains
Crack
propagating
along metallic
grain
boundaries
Intergranular
Initial Development
• Previous finite element study had shown that
anomalous crack propagation occurred at prior
plastic strains of around 5%
• New atmospheric test developed to emulate
chloride contamination on the exterior of
primary circuit
• Conditions under which severe transgranular
SCC occurred established
• Full factorial study planned to distinguish
between the interacting factors controlling crack
propagation rates.
Bent Beam Test
Test Configuration
2.5 Days 180MPa 3% Strain
Initiation at Pitting
Shallow Crack Propagation
Typical
Crack
Front
Crack tip
propagating to
within 0.2mm of
the far side of the
specimen
Crack Propagation Rate with variation of Applied Stress
and 5% prior strain
8
7
Crack propagation rate microns/hour
6
5
4
3
2
1
0
0
20
40
60
80
100
Stress MPa
120
140
160
180
200
The Influence of Humidity on Crack Propagation
12
Crack Propagation Rate microns/hour
10
8
70% 60MPa
70% 120MPa
6
30% 60MPa
30% 120MPa
16% 60MPa
16% 120MPa
4
2
0
0
1
2
3
Prior Strain %
4
5
6
Factorial Investigation
Inputs
Levels
Stress
Strain
Temp
Humidity
60 MPa
0%
0.5%
60ºC
30%
120MPa
1%
75ºC
2%
5%
90ºC
70%
Factorial Study 70% Humidity
25
Crack Propagation Rate microns/hour
20
15
70% 60MPa 90°C
70% 120MPa 90°C
70% 60MPa 75°C
70% 120MPa 75°C
70% 60MPa 60°C
10
70% 120MPa 60°C
5
0
0
1
2
3
Prior Plastic Strain %
4
5
6
Factorial Study 30% Humidity
30
Crack Propagation Rate microns/hour
25
20
30% 60MPa 90°C
30% 120MPa 90°C
15
30% 60MPa 75°C
30% 120MPa 75°C
30% 60MPa 60°C
30% 120MPa 60°C
10
5
0
0
1
2
3
Prior Plastic Strain %
4
5
6
FIB Milled Section of Crack Tip
thanks to:
Dr Ian Giles
Dr Paul Chard-Tuckey
Dr Mike Edwards
Any Questions?
Corrosion Enhanced Plasticity Model
The corrosion
enhanced
plasticity
model
Magnin et
al.(1996)