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Assessment of Effects of Cavities and Narrow Channels on CP Design in the Marine Environment

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General effects caused when cavities and narrow channels/annuli are present in marine structures. A series of computer-based parameter studies is performed.  Also,  investigated are effects of geometry on current flowing through a hole in a plate.

 

Product Number: 51317--9275-SG
ISBN: 9275 2017 CP
Author: Tim Froome
Publication Date: 2017
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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.The formulae cannot 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.In some situations it may be judged that cathodic protection is not required on some surfaces but recommended practise is that current drain to such surfaces needs to be taken into account in the design.This paper first investigates the general effects caused when cavities and narrow channels/annuli are present and attempts to identify patterns of behaviour. A series of computer-based parameter studies is performed in which for example separation between two structural surfaces is varied and the extent of the protected area is measured.Secondly this paper investigates effects of geometry on current drain to surfaces which do not need to be protected. Again computer-based studies are used and for example the size of holes in mud-mats is varied and the current drain to buried surfaces is measured.

Key words: IR drop, constricted flow, CP design

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.The formulae cannot 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.In some situations it may be judged that cathodic protection is not required on some surfaces but recommended practise is that current drain to such surfaces needs to be taken into account in the design.This paper first investigates the general effects caused when cavities and narrow channels/annuli are present and attempts to identify patterns of behaviour. A series of computer-based parameter studies is performed in which for example separation between two structural surfaces is varied and the extent of the protected area is measured.Secondly this paper investigates effects of geometry on current drain to surfaces which do not need to be protected. Again computer-based studies are used and for example the size of holes in mud-mats is varied and the current drain to buried surfaces is measured.

Key words: IR drop, constricted flow, CP design

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