The Use of Cathodic Protection for External Corrosion Protection of Pipelines – the Experiences in Hong Kong

Abstract

The common on-line rehabilitation methods for mild steel pipelines, such as protective coating and lining, usually provide protection from inside the pipes. In such a case, corrosion of the pipes can still continue from outside the pipe, leading to its eventual failure. Therefore, internal protective coating / lining alone is not sufficient and corrosion protection for the exterior of the pipe also needs to be implemented. Cathodic protection is a technology based on electro-chemical principles and is an effective method of protecting pipelines against external corrosion. Hong Kong has an extensive water supply network with a substantial portion of pipe constructed more than 30 years ago. Many pipes are subject to external corrosion problems. Many pipe burst and water leakage cases are reported every year. Recently, Hong Kong government has adopted cathodic protection technology to protect the pipe network against external corrosion. In this paper, the basic principles of cathodic protection are introduced. The selection of the system, factors influencing the design and criteria for acceptance are discussed. Finally, a case study is presented with respect to considerations in design, installation and commissioning of the works.