Crack growth rate (CGR) testing was conducted with the objectives to study the effect of specimen size and to better define the stress intensity factor (K) validity limit for stress corrosion cracking (SCC) of austenitic stainless steel.
Twelve compact tension (CT) specimens of Type 316L, tensile strained to 10% elongation, were tested in simulated boiling water reactor (BWR) normal water chemistry (NWC). Three different specimen sizes were tested: eight 0.5TCT (B=12.5 mm, W=25 mm) specimens covering K in the range 17.7 to 48.3 MPa√m, one 1TCT (B=25 mm, W=50 mm) specimen tested at K from 23.4 to 31.8 MPa√m, and three 1.5TCT (B=37.5 mm, W=75 mm) specimens at Ks ranging from 17.2 to 33.5 MPa√m.
Intergranular stress corrosion cracking (IGSCC) was observed in all specimens, with a tendency for the two smaller specimen sizes to crack faster and at similar rates. However, the difficulty in establishing sustained crack growth under constant K and the incomplete engagement of intergranular cracking across the full thickness of the larger specimens probably led to underestimation of the true CGR. The K validity criterion according to ASTM E399 is very conservative and the limit can be exceeded by more than 200%.