scholarly journals Environmentally assisted cracking in the low pressure superheated hydrogen steam

2021 ◽  
Vol 65 (1) ◽  
pp. 23-32
Author(s):  
Jaromír Janoušek
Keyword(s):  
Stainless Steel ◽  
Crack Initiation ◽  
Low Pressure ◽  
Extension Rate ◽  
Pressurized Water ◽  
Dissociation Pressure ◽  
Environmentally Assisted Cracking ◽  
316L Austenitic Stainless Steel ◽  
Nickel Base

Abstract Low pressure superheated H2-steam appears to be an interesting alternative to pressurized water environments, since it is capable of performing accelerated environmentally assisted cracking (EAC) experiments for nickel base and stainless steel alloys. Constant Extension Rate Tensile (CERT) tests were performed with displacement rates of 2×10-6 or 2×10-8 ms-1 at 350, 400, 440 and 480 °C on flat tapered specimens of Type 316L austenitic stainless steel. The tapered shape allows the determination of crack initiation over a range of stresses and strains simultaneously on one specimen and therefore the threshold stress value was obtained. The environment was 6 times more oxidizing than the dissociation pressure of NiO. The acquired mechanical properties are summarized and threshold stresses for EAC crack initiation are evaluated.

Crack Growth Rates of Alloy 600 From the Davis-Besse Reactor CRDM Nozzle #3 in PWR Environment

2005 ◽  
Author(s):  
Omesh K. Chopra ◽  
Bogdan Alexandreanu ◽  
William J. Shack
Keyword(s):  
Crack Growth ◽  
Potential Drop ◽  
Compact Tension ◽  
Constant Load ◽  
Alloy 600 ◽  
Pressurized Water ◽  
Control Rod ◽  
Environmentally Assisted Cracking ◽  
Water Reactors ◽  
Nickel Base

Reactor–vessel internal components made of nickel–base alloys are susceptible to environmentally assisted cracking. A better understanding of the causes and mechanisms of this cracking may permit less conservative estimates of damage accumulation and requirements on inspection intervals of pressurized water reactors (PWRs). This paper presents crack growth rate (CGR) results for Alloy 600 removed from nozzle#3 of the Davis–Besse (D-B) control rod drive mechanism (CRDM). The tests were conducted on 1/4-T or 1/2-T compact tension specimens in simulated PWR environment, and crack extensions were determined by DC potential drop measurements. The experimental CGRs under cyclic and constant load are compared with the existing CGR data for Alloy 600 to determine the relative susceptibility of the D-B CRDM nozzle alloy to environmentally enhanced cracking. The CGRs under constant load for the nozzle material are higher than those predicted by the best-fit curve for Alloy 600 at 316 °C. The results also indicate significant enhancement of CGRs under cyclic loading in the PWR environment. Characterization of the material microstructure and tensile properties is described.

scholarly journals Environmentally assisted cracking of T91 ferritic-martensitic steel in heavy liquid metals

2020 ◽  
Vol 38 (2) ◽  
pp. 183-194 ◽  
Author(s):  
Anna Hojná ◽  
Patricie Halodová ◽  
Michal Chocholoušek ◽  
Zbyněk Špirit ◽  
Lucia Rozumová
Keyword(s):  
Crack Initiation ◽  
Martensitic Steel ◽  
Liquid Metals ◽  
High Stress ◽  
Flow Speed ◽  
Heavy Liquid ◽  
Extension Rate ◽  
Oxygen Control ◽  
Environmentally Assisted Cracking ◽  
Static Conditions

AbstractIn order to advance material development for future nuclear systems, an insight into the cracking conditions of T91 ferritic-martensitic steel in heavy liquid metals (HLM) is provided. The paper critically reviews previous experimental data and summarizes them with new results. The new testing of T91 steel was performed in contact with slow flow and static HLM to study crack initiation, especially in liquid PbBi eutectic at 300°–350°C and Pb at 400°C with about 1 × 10−6 wt.% of oxygen. Pre-stressed coupons were exposed to the liquid metals for up to 2000 h. Constant extension rate tests (CERTs) were performed in the liquid metals to accelerate cracking development. Under static conditions, the testing resulted in oxidation without any crack observation. Under the CERT ones, the T91 steel showed a tendency to crack initiation in PbBi, while in Pb, cracks were not initiated even when the oxide layer was broken. Moreover, the environmentally assisted crack initiated at the maximum load and continued to grow under further loading without unstable failure. Both previous and new data have confirmed that high stress and plastic strain are pre-conditions for the environmentally assisted cracking of T91 in static HLM. It indicates that in the systems utilizing continuous oxygen control of HLM, the LME/EAC of the T91 could develop only in the beyond design load conditions. Further testing is necessary to address the HLM flow speed effect.

Fatigue Crack Initiation of 304L Stainless Steel in Simulated PWR Primary Environment: Relative Effect of Strain Rate

2012 ◽  
Author(s):  
Nicolas Huin ◽  
Kazuya Tsutsumi ◽  
Laurent Legras ◽  
Thierry Couvant ◽  
Dominique Loisnard ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Initiation ◽  
Strain Rate ◽  
Early Stage ◽  
Laboratory Data ◽  
Fatigue Crack Initiation ◽  
304L Stainless Steel ◽  
Pressurized Water

The French Regulatory Commission insisted on a survey justifying the assumed mechanical behavior of components exposed to Pressurized Water Reactor (PWR) water under cyclic loading without taking into account its effect. In the US and Japan, the fatigue life correlation factors, so called Fen, are formulated and standardized on the basis of laboratory data to take into account the effect on fatigue life evaluation. However, the current fatigue codification, suffers from a lack of understanding of environmental effects on the fatigue lives of stainless steels in simulated hydrogenated PWR environments. Samples tested in a recent study were analyzed to highlight the strain rate effect (within a range 0.4%/s to 0.004%/s) at the early stage of fatigue life in PWR primary environment for a 304L stainless steel. The deleterious effect of PWR primary environment on fatigue crack initiation was observed with a quantitative microscopic approach. Multi scale observations of oxide morphology and microstructure were carried out from common optical microscopy using recent technologies such as 3D oxide reconstruction, and DualBeam observations.

scholarly journals A STOCHASTIC MODEL FOR CRACK INITIATION LIFE PREDICTION OF AN AUSTENITIC STAINLESS STEEL UNDER CONSTANT AMPLITUDE LOADING

2020 ◽  
Vol 14 (1) ◽  
pp. 29-36
Author(s):  
R. Yahiaoui ◽  
R. Noureddine ◽  
B. Ait Saadi
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Crack Initiation ◽  
Stochastic Model ◽  
Critical Length ◽  
Distribution Law ◽  
Safety And Reliability ◽  
316L Austenitic Stainless Steel ◽  
Crack Initiation Life ◽  
High Level

Predicting crack initiation life (CIL) of a mechanical component or a structure in service remains difficult since the crack formation process is of stochastic nature. To ensure a high level of safety and reliability, it is essential to have an appropriate probability distribution law of the CIL to ensure that cracks can be detected before reaching a critical length. In the present study, a stochastic model is used to predict the number of cycles corresponding to the formation of a crack 500 μm long resulted from the nucleation, growth, and coalescence of multiple microcracks. The model is applied in the case of a 316L austenitic stainless steel for different plastic strain ranges.

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