Hydrogen embrittlement is a mechanism by which hydrogen enters a metal, causing a loss in strength and ductility. This phenomenon is of great concern to the oil and gas industry as deep-sea wells operate in high temperature, highly acidic and high stress conditions. Nickel-based superalloys are ideal for use in such environments due to their high strength and exceptional resistance to both corrosion and hydrogen embrittlement. Alloy 945X is a newly developed nickel-based superalloy that has been specifically designed for use in downhole applications. This thesis compares the performance of hydrogenated Alloy 945X with the more established oil and gas grade Alloy 718. The hydrogenating environment of an oil well was simulated via cathodic polarisation. The effect of hydrogen content on the tensile performance of both alloys was studied, alongside fracture and microstructural analysis. A new video-recording technique was employed to investigate the crack initiation and propagation behaviour of both alloys, alongside in-SEM tensile testing. The diffusive nature of hydrogen in Alloy 945X and Alloy 718 was explored. With the use of a ppm-sensitive hydrogen analyser, it was possible to measure the rate at which hydrogen enters and outgassed from both materials as well as the saturation conentrations. Outgassing behaviour was also examined using X-ray diffraction and nano-indentation. The depth of brittle fracture in cathodically charged tensile specimens was correlated with Fickâs diffusion calculations and the critical concentration for embrittlement calculated. In a similar method, a parameter (based on diffusion coefficient calculations) that describes the rate of embrittlement in a material was proposed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:728041 |
| Date | January 2017 |
| Creators | Brown, Michael |
| Contributors | Engelberg, Dirk |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/on-the-hydrogen-embrittlement-of-oil-and-gas-grade-alloy-718-and-alloy-945x(e0831365-5b30-48e1-ad54-6b03aa3a6763).html |
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