Corrosion Behavior of Austenitic Stainless Steels in Oxidizing and Reducing Gases Relevant to Oxyfuel Power Plants

Stress Corrosion Cracking (SCC) has been observed in some components of austenitic stainless steels in the Boiling Water Reactors (BWRs). The structural integrity evaluation for flawed component is performed for continued service for a specified time period based on the Rules on Fitness-for-Service (FFS) for Nuclear Power Plants, such as JSME FFS Code or ASME Section XI. SCC growth evaluation is generally performed only by taking into account steady loads, such as welding residual stress. It is important to examine various factors affecting SCC growth behavior for further understanding and improvement in predicting growth behavior in the BWR environment. Cyclic overloading due to such as earthquake force is one of the important factors to be evaluated. In this study, the effect of cyclic overload on SCC growth in simulated BWR environment has been examined by using CT specimens of cold-rolled stainless steels (Type 316L). The retardation phenomenon was observed in SCC growth behavior immediately after the cyclic overloading was applied. It was considered that SCC propagation was retarded due to the compressive plastic region at the crack tip, introduced by overloads. The method of predicting the SCC growth behavior after cyclic overloading was also discussed.

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Influence of Impurities on Intergranular Corrosion of Extra High Purity Austenitic Stainless Steels

Volume 1: Plant Operations, Maintenance, Engineering, Modifications and Life Cycle; Component Reliability and Materials Issues; Next Generation Systems ◽

10.1115/icone17-75531 ◽

2009 ◽

Author(s):

Ikuo Ioka ◽

Jun Suzuki ◽

Takafumi Motoka ◽

Kiyoshi Kiuchi ◽

Junpei Nakayama

Keyword(s):

Corrosion Rate ◽

Corrosion Behavior ◽

Stainless Steels ◽

High Purity ◽

Intergranular Corrosion ◽

Active Sites ◽

Degradation Mechanism ◽

Austenitic Stainless Steels ◽

Hno3 Solution ◽

Nuclear Fuel Reprocessing Plant

An intergranular corrosion is observed in austenitic stainless steels exposed to high temperature, concentrated nitric acid (HNO3) solution with highly oxidizing ions. It is an important degradation mechanism of austenitic stainless steels for use in a nuclear fuel reprocessing plant. The intergranular corrosion is caused by the segregation of impurities to grain boundaries and the resultant formation of active sites. Extra High Purity (EHP™) austenitic stainless steel was developed with conducting the new multiple refined melting in order to suppress the total harmful impurities less than 100ppm. The intergranular corrosion behavior of EHP alloys with various impurities was examined in boiling HNO3 solution with highly oxidizing ions to find a correlation between the intergranular corrosion and the impurities of EHP alloys. A good correlation was confirmed between the degree of intergranular corrosion and the corrosion rate. The relationships between the corrosion rate and the impurities content of EHP alloys was determined using a multiple regression analysis. The influence on corrosion rate became small in order of B, P, Si, C, S and Mn. It was important to control B in intergranular corrosion behavior of EHP alloys.

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