In early 2017 at the NACE Corrosion Conference in New Orleans BEASY staff presented some recent developments and applications in the technical sessions and exchange groups. It was great to meet many friends at the conference and discuss how modelling can be used to improve and optimize CP systems as well as providing further confidence in their performance.
Assessment of Effects of Cavities and Narrow Channels on CP Design in the Marine Environment
Underwater termination assembly, mud mat, split casing, armour
termination and bend limiters being readied for deployment.
At this year NACE John Baynham and Tim Froome presented an interesting paper on the difficulties presented by the geometry of certain structures in obtaining adequate CP protection.
CP system design work in the marine environment makes use of structure surface area, required current density, and anode resistance formulae to select the number and mass of anodes required to protect a structure. These formulas do not take account of restrictions to current flow caused by close proximity of structural surfaces to each other, and consequently CP systems which have been designed in the recommended way may sometimes not protect parts of a structure.
This paper investigates the protection provided to the structure when cavities and narrow channels/annuli are present, and identifies patterns of behaviour. A series of computer-based parameter studies was performed in which, for example, separation between two structural surfaces is varied, and the extent of the protected area is determined. The paper also investigates effects of geometry on current flowing through a hole in a plate. This situation frequently occurs in design of mud-mats - when the interest is to determine current drain to buried surfaces, and sometime occurs when free flooding cavities need to be protected. Again computer-based studies are used, and for example the size of the hole is varied.
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