Abstract
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 SO42- at
230-290oC.
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.
Ferritic low activation steel F82H (in tempered
condition) is not susceptible to stress corrosion
cracking under static loading conditions in high
temperature water. However, its fracture resistance is
clearly lower in water than in inert environment.
Even as low an amount as 10 ppb SO42- in the otherwise
pure BWR water results in one order of magnitude higher
stress corrosion crack growth rate than the crack growth
rate is in the pure water. Higher sulphate concentrations
do not increase the crack growth rate further. Inconel 82
weld metal is much more resistant to stress corrosion
cracking than Inconel 182 weld metal. No relevant crack
growth rates could be measured for Inconel 82 weld metal
in this work.
Cold-worked (20%) AISI 316 steel is susceptible to
intergranular stress corrosion cracking in BWR water.
Sulphate in BWR water increases the crack growth rate
also for AISI 316 steel. However, the observed effect was
not as pronounced as for Inconel 182 weld metal.
The results indicate that the same crack growth rates can
be obtained using small SEN(B) specimens under
elastic-plastic loading conditions and large specimens
predominantly under linear-elastic loading conditions.
The crack growth rates of the studied IGSCC susceptible
materials were independent of the stress intensity factor
level, KJ or KI, in the studied stress intensity ranges.
At very low J-integral increase rates, the crack growth
rate is linearly dependent on the loading rate.
Loading rate may be a better parameter to correlate with
the crack growth rate than the load, e.g., stress
intensity factor. The observed dependence between crack
growth rate and dJ/dt implicates that the specimen size
has an effect on the crack growth rate in constant load
tests. In constant load tests the specimen size, dJ/dt
and crack growth rate are interconnected.
Original language | English |
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Qualification | Doctor Degree |
Awarding Institution |
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Supervisors/Advisors |
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Award date | 18 Jun 2004 |
Place of Publication | Espoo |
Publisher | |
Print ISBNs | 951-38-6382-4 |
Electronic ISBNs | 951-38-6383-2 |
Publication status | Published - 2004 |
MoE publication type | G4 Doctoral dissertation (monograph) |
Keywords
- stress corrosion cracking
- stress corrosion testing
- linear-elastic fracture mechanics
- elastic-plastic fracture mechanics
- boiling water reactors
- stainless steel
- nickel-base weld metal
- crack growth rate
- fracture surface morphology