PhD Studentship (Sponsored by Lloyds Register Foundation) Local detection of hydrogen in steels using neutron diffraction imaging

Course Description

Background

Steels used in offshore flowlines, pipelines and risers are susceptible to corrosion fatigue in the presence of hydrogen sulfide (H2S) and moisture present in oil and gas production fluids. A critical feature in the mechanism of failure involves hydrogen diffusion and embrittlement of the steels. Furthermore, hydrogen generated from the electrochemical reactions during cathodic protection of pipelines can diffuse into and embrittle the steel, particularly at regions of high tensile stress. The relationship between the amount of hydrogen in the steel and fatigue crack initiation and/or propagation rate is not fully understood. Previously only bulk hydrogen in steel was measured and this was correlated to fatigue crack growth rates (FCGRs). Furthermore, methods to detect and quantify the local accumulation of hydrogen at flaws, corrosion pits or crack tips, have not been previously been investigated.

Neutron diffraction imaging, a non-destructive testing method, is a particularly useful technique which exploits the ability of neutrons to both penetrate metals and detect light elements contained therein, such as hydrogen, carbon and nitrogen. The primary goal of this PhD project is to establish the effectiveness and sensitivity of neutron diffraction for local detection of hydrogen at crack tips, flaws or corrosion pits. As X65 steel is commonly used in pipelines or marine structures, this project will help demonstrate the relationship between local accumulation of hydrogen rather than bulk hydrogen on FCGRs. The data generated will be used to validate new or existing models of hydrogen effects on fatigue propagation rates.

Project Outline

The PhD project will begin with neutron diffraction calibration studies on hydrogen charged steel, by conducting in-situ tests on strained and unstrained material exposed to seawater environments with CP. The sensitivity of the neutron diffraction imaging method will be established for the local detection and quantification of hydrogen in steels. A comparison of this method and bulk hydrogen detection methods will be made. Once the sensitivity of the method is validated, the study can focus on local detection of hydrogen ahead of crack tips and correlate the concentration of hydrogen with crack growth rates in order to underpin the main mechanism or driving force for crack propagation. FCGRs in sour environments will also be investigated with relation to hydrogen concentrations at crack tips.

This work will be augmented with studies modelling diffusion of hydrogen in materials under specific material stress/strain states and environmental conditions. The relationship between local accumulation of hydrogen and residual stresses at weld toes/crack tips on FCGRs will be studied by interrupted FCGR testing in seawater environments with CP. The neutron diffraction studies will be conducted at the ISIS Neutron and Muon Source (Oxfordshire).

About Industrial Sponsor

The Lloyd’s Register Foundation funds the advancement of engineer-related education and research and supports work that enhances safety of life at sea, on land and in the air, because life matters. Lloyd’s Register Foundation is partly funded by the profits of their trading arm Lloyd’s Register Group Limited, a global engineering, technical and business services organisation.

About NSIRC

NSIRC is a state-of-the-art postgraduate engineering facility established and managed by structural integrity specialist TWI, working closely with, top UK and International Universities and a number of leading industrial partners. NSIRC aims to deliver cutting edge research and highly qualified personnel to its key industrial partners.

About the University

The University of Leicester is a leading UK university (34th in the Complete University Guide) committed to international excellence through the creation of world changing research and high quality, inspirational teaching. Leicester is consistently one of the most socially inclusive of the UK’s leading universities with a long-standing commitment to providing fairer and equal access to higher education. In terms of research, Leicester is ranked in the top 25 universities in the Times Higher Education REF Research Power rankings. 75% of the research was judged to be internationally excellent.

Candidate Requirements

Candidates should have a relevant degree at 2.1 minimum, or an equivalent overseas degree in engineering or materials science. Candidates with suitable work experience and strong capacity in numerical modelling and experimental skills are particularly welcome to apply. Overseas applicants should also submit IELTS results (minimum 6.5) if applicable.