Stress corrosion crack growth rate measurement in high temperature water using small precracked bend specimens

摘要

The applicability of elastic-plastic fracture mechanics to stress corrosion crack growth rate measurements was studied. Several test series were performed on small elastic-plastically loaded SEN(B) specimens in high temperature water. One test was performed on a 25 mm C(T) specimen under linear-elastic loading. The tests on the SEN(B) specimens were performed using either rising displacement or a combination of rising and constant displacement loading. The test on the 25 mm C(T) specimen was performed using a combination of constant load and constant displacement. The studied materials were AISI 304 steel in sensitized, mill-annealed and irradiated conditions, AISI 316 in cold-worked condition, Inconel 82 and 182 weld metals in as-welded and thermally aged conditions and ferritic low activation steel F82H in tempered condition. The crack growth rate tests were performed in simulated pure BWR water and simulated BWR water with 10-100 ppb SO_4~(2-) at 230-290℃. It was shown that intergranular stress corrosion cracking susceptibility can be determined using an elastic-plastic fracture mechanics approach. Fracture surface morphology in sensitized AISI 304 and welded AISI 321 steels depends on the applied loading rate in BWR water. The fracture surface morphology changes from transgranular to intergranular, when J-integral increase rate is decreased. However, extremely slow displacement rate is needed for the fracture surface morphology to be fully intergranular. Rising J results in transgranular stress corrosion cracking (or strain-induced corrosion cracking) also in the mill-annealed AISI 304 and 321 steels. Tests on irradiated AISI 304 steel showed that welding together with exposure to low neutron fluence in the BWR operating conditions results in a higher susceptibility to stress corrosion cracking than welding or irradiation alone.