SCC growth rate quantification in CW 316L stainless steel in PWR primary water using reduced size compact tension specimens

The stress corrosion cracking (SCC) growth rate behaviour of 40% cold-worked (CW) 316L stainless steel (SS) in simulated PWR primary water was investigated using reduced size disk compact tension (DCT) specimens. DCT specimens were pre-cracked in air at room temperature to an a/w ratio of 0.53 by fatigue at 8Hz and R=0.7 at decreasing ∆K from 16 MPa m down to 11 MPa m. All tests were performed in simulated primary water at 288 C with 1000 ppm of boric acid, 2 ppm of lithium hydroxide and an hydrogen content of 30 cc(STP)/kg of water. Prior to SCC growth tests, triangular cycling was applied to all specimens in the test environment for 24 hours at 10-3 Hz and R=0.7. SCC growth tests were conducted using trapezoidal loading (500s rise C 9000s hold C 500s decrease) at R=0.7 in the K range 20 MPa¡Ìm to 30 MPa¡Ìm for approximately 1600 hours. Continuous monitoring of the crack growth was performed by DCPD technique. The fracture surface of the specimens tested at 25 MPa m and 30 MPa m both exhibited an area of uniform crack propagation and several areas of localized (finger-like) IG crack propagation extending far beyond the area of uniform crack propagation. For these two tests, the crack length measured by DCPD was in good agreement with the crack length corresponding to the uniform crack propagation area. CGR ranging from 1.6 10-8 mm/s to 4.2 10-8 mm/s were detected. In contrast, the fracture surface of the specimen tested at 20 MPa m only exhibited several areas of localized (finger-like) IG crack propagation and no uniform crack propagation. For this test, no crack extension was detected by DCPD.