Stress corrosion cracking of candidate waste container materials; Final report Page: 69 of 86
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61
4 Fracture-MechanIcs Crack-Growth-Rate Tests
4.1 Experimental Procedures
Compact tension (CT) specimens of 25.4 mm thickness were machined from 25.4-mm-
thick plates of Type 304E SS (Heat No. V70200), Type 316L SS (Heat No. 16650), and
Incoloy 825 (Heat No. HH2125F). The materials were tested in the as-received mill-
annealed condition without additional heat treatment. Elemental composition and
mechanical properties of the materials are shown in Tables 2-9.
Side grooves having a semicircular cross section were cut into both sides of the
specimen to a depth of 1.27 mm to restrict crack growth to a single plane. The design of
the CT specimens is in accordance with the ASTM specification E399,14 except fo. the
side grooves and six small threaded holes on the front face for instrumentation, as shown
in Fig. 57. The stress intensity factors were calculated according to ASTM specification E-
399. The direction of crack extension was perpendicular to the short transverse thickness
direction of the plates. Rolling direction of the plates was not provided by LLNL or the
vendors. Metallographic examination of the materials did not reveal any clues for rolling
direction.
The specimens were fatigue-precracked in air at room temperature for a length of
1.91 mm to introduce a sharp starter crack The initial machine notch measured from the
load line was 17.78 mm. An isosceles triangular loading waveform at a frequency of 1-2 Hz,
a load ratio R (a ratio of minimum to maximum load) of 0.25, an initial maximum stress
intensity of 16.1 MPam i/2 and a final maximum stress intensity of 17.5 MPa-m1/2 was used
for precracking. This final maximum stress intensity value is 70% of initial peak stress
intensity for the subsequent crack-growth-tests in a simulated J-13 well water.
The initial peak stress intensity value for the tests in the simulated J-13 well water
was chosen to be about 25 MPa~r1/2. Welding residual stresses are the most important
driving force for cracks. Under these loads, the largest marginally detectable defects that
would be created during the fabrication of a waste container would have associated stress
intensity values approximately half the value chosen for these tests, which provides some
conservatism.
The CGR tests were performed in a 5-L nickel vessel with a once-through flow
system at a flow rate of 3 mL/min, under 1 atm pressure at 92-94 C. The vessel was not
hermetically sealed. The simulated J-13 well water was prepared from deionized high-
purity water (resistivity >16 M(1-cm) and reagent-grade-purity salts of CaSO4, Ca(NO3)2,
CaCi2, FeCl2, Li2SO4, MgSO4, MnSO4, AlCl3, Na2CQ3, NaHCO3, KHCO3, Na2SiO3, and HF.
High-purity mixed gas containing 20% 02, 12%C02, and 68% N2 was used as a cover gas at
3-5 psig to maintain the desired dissolved 02 and HC03 concentrations. Table 23 shows a
typical composition of J-13 well water and analysis results for the simulated test solution
used for the CGR tests. The test solution is a good simulation of the ionic and dissolved
gaseous species in the J-13 well water, with the exception of the Si concentration. Si was
not ieiei tn the test solution to avoid precipitation of silicate. Silicates are commonly
used as corrosion inhibitors for low-temperature applications,12.13 and it is considered
unlikely that silicates would contribute to environmentally assisted crack growth of the test
materials. The higher pH25*C values for the effluent test solution are due to some loss of
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Park, J. Y.; Maiya, P. S.; Soppet, W. K.; Diercks, D. R.; Shack, W. J. & Kassner, T. F. Stress corrosion cracking of candidate waste container materials; Final report, report, June 1, 1992; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc625520/m1/69/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.