Abstract
In 1992, as part of the ongoing pipeline integrity program conducted by a oil producing affiliate associated with one of the author’s employers, cathodic protection surveys were conducted on 77 subsea pipelines. These pipelines ranged in length from 0.5 to 35 km (.3 to 22 miles), in diameter from 4-inch to 42-inch (100 to 1070 mm) and in age from new to over 30 years. As would be expected with some of the pipelines operating beyond the original design life of the as installed anodes, decreasing levels of protection were found on some of the older pipelines, which justified the installation of retrofit anodes. Anodes were retrofit on a number of pipelines to boost the levels of protection.
All existing pipelines, now numbering 100, were resurveyed in during 2003. The overall levels of protection were found to be quite good, with only a couple of pipelines that required further retrofit attention. However, with an inventory of aging pipelines and the high cost of installing retrofit anode sleds on offshore pipelines, a study was conducted to determine what could be learned from the survey data that would help optimize the design and installation of future retrofits. This paper discusses the methods used to analyze the survey results of the study and some of the learnings from the study that will influence further offshore CP evaluations.
