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Title: Modelling of carbonate-bicarbonate stress corrosion cracking of pipeline steels
Author: Alkathafi, Maftah Hussien Abdulgader
ISNI:       0000 0004 2668 819X
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2009
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This research work has been concerned with the physical and numerical modelling of the conditions developed under disbonded coatings on steel, with a view to understanding the processes responsible for the conditions that lead to carbonate-bicarbonate stress corrosion cracking. The physical model has used a polyethylene coating covering a crevice of controlled thickness, with a controlled gas connposition (air with 1% CO₂) on the exterior of the coating. An optical fibre chemical sensor was developed to monitor the pH at locations along the crevice, and the potential has been monitored at the same locations using salt-bridge to conventional reference electrodes. A mathematical model of the same system has been developed using a commercial finite element package. The model was based on a one-dimensional crevice and results have been obtained for a high and a low permeability of coating. The results showed that the permeability of the coating plays an important role in controlling the conditions at the end of the crevice. At a high h permeability of coating the gas transport through the coating creates more alkaline solution inside the crevice, the generation of hydroxyl ions due to the oxygen reduction reaction increasing the pH. With a low permeability coating, no gas diffusion through the coating occurs, and the solution inside the crevice becomes less alkaline where the iron dissolution reaction takes place. So the pH and potential inside the crevice with a high permeability coating were greater than with the low permeability coating. In addition, the carbonate and bicarbonate ion concentrations were also higher with the high permeability coating. The results of this model were in good agreement with the physical model and with mathematical models reported in the literature.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available