Understanding the High Temperature Hydrogen Attack of Steels Utilizing Novel In Situ Analytical Transmission Electron Microscopy Techniques

Abstract

The high temperature hydrogen attack (HTHA) of low alloy steels can result in the severe and unexpected structural failure of large petrochemical components. HTHA is a difficult to detect and monitor phenomena, of which there is poor scientific understanding of the underlying mechanism of its occurrence. The safe operation of materials in high temperature hydrogen (HTH) environments is governed by Nelson Curves, a series of plots of industrial failures related to HTHA. Nelson curves are increasingly revised downwards as HTHA repeatedly occurs unexpectedly within industry due to a fundamental lack in understanding as to its mechanism. Considerable work has been carried out previously looking at advanced HTHA exposed material but the mechanism behind the initiation of HTHA at the nano scale is not fully understood. In situ transmission electron microscopy (TEM) has become an increasingly important tool in the understanding of dynamic phenomena. Utilizing specialised in situ holders and hybrid sample preparation procedures, developed at the University of Manchester, it is now possible to examine metal-gas reactions in situ within the microscope. This work demonstrates that in situ scanning transmission electron microscopy (STEM) is an effective tool in enabling the direct observation of the chemical reaction of steel Fe3C carbides with HTH. Notably the direct reaction of carbides is demonstrated and experimental techniques refined to enable the visualisation of strain and dislocations formation at carbide-matrix interfaces. Furthermore, the initial formation of nano-scale cavitation on both steel carbides and grain boundary interfaces is demonstrated and the relationship between methane cavitation, density, and distance from a hydrogen exposed surface examined.

Date of Award	1 Aug 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Grace Burke (Supervisor) & Brian Connolly (Supervisor)