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 Crack propagating along metallic grain boundaries Metallic Grains Grains Crack propagating across grains Transgranular 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

Factorial Investigation InputsLevels Stress60 MPa120MPa Strain0%0.5%1%2%5% Temp60ºC75ºC90ºC Humidity30%70%

FIB Milled Section of Crack Tip

Any Questions? thanks to: Dr Ian Giles Dr Paul Chard-Tuckey Dr Mike Edwards

Corrosion Enhanced Plasticity Model The corrosion enhanced plasticity model Magnin et al.(1996)