3D evaluation of the oxidation and porosity in 9Cr tubing using FIB and X-ray

Abstract

A combination of focussed ion beam milling and X-ray tomography has been used to evaluate the steam grown oxide on plant-exposed Grade 91 material, comparing the features observed with those on laboratory coupons, which have not been ground. A particular focus was the characterisation of any pre-existing oxides and features; and the effect these have on elemental segregation and the formation of porosity in the Fe–Cr spinel. In particular, X-ray computed tomography (XCT) has been used to characterise the defect structure within the magnetite layer of the scale. The results have shown that laboratory tests on as-received material replicate features seen in plant-exposed material, and that macroscopic crazing-like cracks extend from the surface of the oxide through the spinel layer, and that this provides a mechanism for oxide healing and densification around the cracks.

Keywords:

• FIBSEM
• XCT
• 9Cr steel
• steam oxidation
• voids

Acknowledgements

The authors would like to thank the UK Department for Business, Energy and Industrial Strategy for providing funding and Uniper Limited for the provision of materials via Material‐Component Performance‐driven solution for Long‐Term Efficiency Increase in Ultra Supercritical Power Plants (MACPLUS®) project.