The INCEFA+ project (INcreasing Safety in NPPs by Covering gaps in Environmental Fatigue Assessment) aims to generate and analyse Environmental Assisted Fatigue (EAF) experimental data studying parameters such as mean strain, hold times and surface finish. To understand the implications of these parameters for environmental fatigue assessments, these tests were carried out at 300 °C in air and light water reactor primary coolant environments.

Over the duration of this project around 230 fatigue data points were generated by different organisations using a common testing methodology, but with differing specimen geometries. Of these 230 data points, 23 were obtained from tests done using hollow specimen designs. Recent work comparing the fatigue lives of hollow to those of solid specimens indicates that on average the use of hollow specimens results in reduced fatigue lives. This has been explained in terms of the additional hoop and radial strains applied to the specimen due to the internal pressure of the hollow specimen. Given the examples published in the literature on the topic, the comparison of data generated using hollow and solid specimen geometries within the INCEFA-PLUS database has been a particular concern.

This paper aims to explore the differences between hollow and solid specimen geometries within the INCEFA-PLUS database, highlight the potential risks of including both geometries in a single analysis, and discuss the approach taken by the project to mitigate the identified risks. The work presented in this paper details three approaches for the data obtained from hollow specimens: 1) exclude the data, 2) include the data as is, or 3) include the data with a correction on the strain amplitude. The strain amplitude correction will be based on the theoretical basis presented in Gill et.al. (PVP2017-65975) and extended to account for the different hollow specimen geometries used across the INCEFA-PLUS programme.

This work demonstrates the robustness of the data analysis performed on the INCEFA-PLUS database to the use of differing specimen geometries. It also develops an explanation for the apparent difference in fatigue life between tests conducted on hollow specimens under test conditions that are nominally the same. Furthermore, this paper builds on the mechanistic understanding presented in Gill et.al. (PVP2017-65975) and generalises across several laboratories.


Incefa-Plus Project: The Impact of Using Fatigue Data Generated From Multiple Specimen Geometries on the Outcome of a Regression Analysis

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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