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IN-SITU MAPPING OF LOCALISED CORROSION UNDER THE EFFECT OF STRAIN USING A SCANNING VIBRATING ELECTRODE TECHNIQUE / ROBERTO ANDRADE
Swansea University Author: ROBERTO ANDRADE
Abstract
Stress Corrosion Cracking (SCC) is a type of material degradation characterised by the combined effect of tensile stress and localised corrosion produced by aggressive ions such as chlorides. It is very difficult to detect and has caused catastrophic failures of components in service at diverse indu...
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Swansea University, Wales, UK
2024
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| Institution: | Swansea University |
| Degree level: | Master of Research |
| Degree name: | MSc by Research |
| Supervisor: | Williams, G |
| URI: | https://cronfa.swan.ac.uk/Record/cronfa66610 |
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| Abstract: |
Stress Corrosion Cracking (SCC) is a type of material degradation characterised by the combined effect of tensile stress and localised corrosion produced by aggressive ions such as chlorides. It is very difficult to detect and has caused catastrophic failures of components in service at diverse industries. Several researchers have investigated this phenomenon using different approaches, but therole of the stress in the initiation and propagation stage is still not fully understood.Previous studies have shown that the scanning vibrating electrode technique (SVET) can be used to map pitting corrosion sites on austenitic stainless steels (SS) in nonstrained conditions. The present research looks to expand the scope of this technique, employing SVET analysis of strained and non-strained samples of 304 SS- in the annealed and thermally sensitised condition. Such samples were tested in 3 M and 4 M MgCl2 concentrations, aiming to obtain relevant data that can improvethe understanding of the role of stress in the initiation of pitting corrosion.As part of the experiments carried out, droplet tests were performed on annealed and sensitised samples under strained and non-strained conditions, determining that 4 M MgCl2 was the ideal concentration whereby spontaneous formation of pits in open circuit conditions was reproducibly observed. Subsequently, the samples were immersed in this chloride electrolyte and the localised corrosion behaviour was studied in-situ using the SVET. The current density maps obtained showed that applied strain can decrease the decay rate of anodic current density for the propagating pits compared with the un-strained surface. Additionally, these results were complemented with potentiodynamic polarisation, optical microscopy, scanning electron microscopy and height-depth microscopy, which showed morphologies and other relevant characteristics. The results obtained could open new research lines to investigate the role of stress in the initiation of SCC in nuclearcladding alloys.In a separate experiment, the localised corrosion characteristics of coupons consisting of a bespoke nuclear cladding alloy (20Cr/25Ni/Nb) electron beam welded to a simulant sensitised grain boundary alloy (45Fe/45Ni/10Cr) was carried out. The tests performed included potentiodynamic polarisation studies of the alloy, weld, and simulant grain boundary regions separately along with, SVET andSKP analysis of the test coupon as a whole. Spatially resolved SKP-derived maps determined the relative nobility of the cladding in comparison to the simulant alloy, and SVET studies showed that the weld joint was most susceptible to localised corrosion initiation under immersion conditions. |
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| Item Description: |
A selection of content is redacted or is partially redacted from this thesis to protect sensitive and personal information. |
| Keywords: |
Localised Corrosion, Pitting Corrosion, SCC, SVET, Corrosion under strain |
| College: |
Faculty of Science and Engineering |
| Funders: |
EPSRC, WEFO, National Nuclear Laboratory (NNL) |