This PhD is supervised by Professor Michael Havbro Faber from the Technical University of Denmark and Dr Ujjwal Bharadwaj from TWI
Risk Based Inspection (RBI) planning for offshore structures has over the last 2-3 decades proven to be a very strong tool in the planning of structural integrity management activities. In best practice RBI the uncertainties associated with the fatigue loading, the fatigue crack growth process, the inspection quality and the quality and effects of repair and maintenance activities are modeled by means of random variables. Crack growth models take basis in probabilistic fracture mechanics (FM) crack growth models calibrated to SN fatigue tests results. Moreover, Bayesian updating is utilized to update the probabilistic models using inspection results as well as maintenance actions. Optimal inspection and maintenance plans complying with given requirements to structural reliability and safety for personnel are then identified based on the updated probabilistic models.
Based on experience and new research a number of issues associated with present best practice for RBI have been identified, including:
• SN diagram representations of fatigue test results is not fully consistent with experimental evidence. • Uncertainties associated with modelled crack growth using best practice FM crack growth models appear to be excessively high. • Hot-spot fatigue stresses are associated with significant uncertainties. • Existing generic methods for RBI are hot-spot oriented and only facilitate for a heuristic inclusion of system effects (effect of inspections of one hot spot with respect to modelled performance of non-inspected hotspots).
Focus in the present project is directed on RBI and Maintenance planning for welded details in fixed offshore steel structures with the objective to augment best practice approaches on the following aspects:
• Consistent uncertainty treatment in the modeling of the fatigue lives of welded details • Improved (reduced uncertainty) in the modeling of fatigue crack growth • Utilization of improved knowledge about actual fatigue stresses directly in the RBI process • Consistent modeling and assessment of system effects in inspection planning • Direct inclusion of individual risks to inspections and inspection and maintenance operations in the
Each of the listed points will in themselves be of significant interest for both the research community and for offshore oil and gas operators. It is expected that the results of the project will contribute with significant new knowledge on each of them and also push the industry best practices forwards.
Finally, it is expected that the results of the present project will be incorporated into a tool for generic inspection planning in the form of a test implementation. Based on assessments and studies supported by the developed tool the benefits in terms of improved risk management achieved by the improved approach to RBI will be documented.
Dissemination of the results from the project will be supported by contributions and papers at international conferences and journals of relevance for the offshore engineering community. Moreover, the close collaboration between the hosts of the present PhD research project, i.e. NSIRC and the Danish Hydrocarbon Research and Technology Centre (DHRTC) at the Technical University of Denmark, and the oil and gas industry will ensure a direct channel to end users.
About the 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.
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 Technical University of Denmark (DTU), comprises 18 departments, around 6000 employees, 10000 students and 1000 PhD students. DTU is positioned on the World University Rankings, Engineering and Technology as number 74 in the World, number 20 in Europe and number 2 in the Nordic countries.
Candidates should have a relevant degree at 2.1 minimum, or an equivalent overseas degree in Mechanical, Electrical/Electronics or Civil/Structural Engineering, Material Science, Metallurgy or Physics. 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.
This project is funded by Lloyds Register Foundation, TWI and academic partners. The studentship will provide successful Home/EU students with a stipend of £16k/year and will cover the cost of tuition fees. Overseas applicants are welcome to apply, with total funding capped at £24k/year.