INCEFA-PLUS (Increasing Safety in Nuclear Power Plants by Covering Gaps in Environmental Fatigue Assessment)

INCEFA-PLUS is a major new five year project supported by the European Commission HORIZON2020 program. The project commenced in mid 2015. 16 organizations from across Europe have combined forces to deliver new experimental data which will support the development of improved guidelines for assessment of environmental fatigue damage to ensure safe operation of nuclear power plants. Prior to the start of INCEFA-PLUS, an in-kind study was undertaken by several European organizations with the aim of developing the current state of the art for this technical area. In addition to stress/strain amplitude, this study identified three additional experimental variables which required further study in order to support improved assessment methodology for environmental fatigue, namely the effects of mean stress/strain, hold time and surface finish. Within INCEFA-PLUS, the effects of these three variables on fatigue endurance of austenitic stainless steels in light water reactor environments are therefore being studied experimentally. The data obtained will be collected and standardized in an online environmental fatigue database. A dedicated CEN workshop will deliver a harmonized data format facilitating the exchange of data within the project but also beyond. Based on the data generated and the resulting improvement in understanding, it is planned that INCEFA-PLUS will develop and disseminate methods for including the new data into assessment procedures for environmental fatigue degradation. This will take better account of the effects of mean stress/strain, hold time and surface finish. This paper will describe the background to the project and will explain the expectations for it.

Creep-Fatigue Strength of Sn-8Zn-3Bi Solder Under Multiaxial Loading

This paper describes the multiaxial creep-fatigue of Sn-8Zn-3Bi solder in proportional and non-proportional loadings. Push-pull and reversed torsion tests were carried in proportional test using fast-fast, slow-fast, fast-slow, slow-slow and strain-hold waves. Non-proportional tests were also carried out using box, step and circle strain waves. In proportional test, smallest creep-fatigue lives were observed in push-pull slow-fast test. Creep-fatigue lives in reversed torsion test were longer by a factor of 2 than those in push-pull test compared with the same strain wave. Non-proportional loading reduced the creep-fatigue life. Circle strain wave showed the smallest fatigue life in non-proportional loading. A non-proportional strain proposed by the authors correlated all the proportional and non-proportional fast-fast data within a factor of two scatter band.

Creep and Creep-Fatigue Strength Property of a Long-Term Used Boiler Weldment Parts of 2.25Cr-1Mo Steel

The purpose of this study is to make clear effect of material degradation on creep and creep-fatigue properties of a weldment. Materials used in this study were a weldment of a boiler super header operated for about 200,000 hours (U weld joint) and a simulated as-received weldment (S weld joint). In the U weld joint, although creep cavities were not observed at all, significant coarsening of carbide precipitation and low dense dislocation structure were observed at all locations in the weldment compared with microstructure of the S weld joint. Creep rupture time of the U weld joint is shorter than that of the S weld joint at higher stress region, while the discrepancy of the rupture strength tends to disappear as stress level becomes lower. Strain controlled creep-fatigue tests with 1 hour and 10 hours strain hold time at the maximum tensile strain were performed at strain range of 0.3% and 0.5% on S and U weld joints. No difference of failure life between materials was observed. Reduction in failure life by introducing strain hold period becomes larger as decreasing strain range level indicating that creep-fatigue interaction is enhanced under lower strain range. Based on the nonlinear damage accumulation model, a simplified creep-fatigue life prediction method of weldments under creep-fatigue loading conditions was proposed. It was demonstrated that failure lives under the long-term creep-fatigue conditions were well predicted by the simplified prediction method.