title: Study of cathodic protection related to thermal desalination plant
Creators: name: Najm-Mohammed, Nader Abdulaziz
Publisher: name: University of Glasgow
Year: 1997
Subjects: subject: Chemical engineering.

description: This project comprised an in-depth study of the application of cathodic protection in thermal desalination plant and used as it's based on extensive cathodic protection system in multi stage flash units located at Dubai Aluminium Company in United Arab Emirates. A review of the literature confirmed that the Dubai cathodic protection system is unique since cathodic protection has seen only moderate application in desalination plant and this is particularly true of its application in respect of carbon steel components such as pipe-work. The practical work of the project included a detailed survey and assessment of the performance of the cathodic protection system in the multi stage flash units at Dubai. This confirmed that the system, even after some 15 years of operations, continues to successfully control corrosion in the inside of a wide range of carbon steel components. The examination of cathodically protected components clearly revealed the crucial role of calcareous deposition in the corrosion control process. The major part of the research comprised an in-depth experimental study of cathodic protection in a range of environmental conditions related to thermal desalination plant. This work involved some experiments on a relatively simple laboratory flow loop but with more emphasis on the utilization of a larger rig comprising a pipe 0.25 meter diameter and approximately 15 meter length attached to one of the multi stage flash units at Dubai. The results have provided substantial detailed evidence of the crucial role of calcareous scale deposition on the overall performance, and especially the current/time relations of cathodic protection systems and have significantly extended the knowledge available from previous studies which limited to conditions experienced on offshore installations. The work has involved the study of the influences of set potentials, temperature, flow conditions and cathodic protection control mode (potentiostatic or galvanostatic) on the performance of the cathodic protection system and the deposition characteristic of the calcareous scales. Doubled layered scale, comprises an inner Mg(OH)2 (brucite) and an outer zone of CaCO3 (aragonite) crystals have been identified over a range of conditions and tentative models for the mechanism of growth of the scales have been postulated. Since both phases of the research had confirmed the technical success of cathodic protection for protecting carbon steel components in thermal desalination plant, the final part of the work comprised a cost comparison study. This was focused on a pipe loop containing a number of fittings and the findings indicated that carbon steel protected by cathodic protection is considerably less costly then stainless steel for high temperature parts of multi stage flash plant but that glass reinforced epoxy pipes are likely to be cheaper than cathodically protected carbon steel unless modes of cathodic protection operation can be identified that successfully protect with lower capital cost.