Need: Cased carrier pipes at railroad and highway crossings exist under a multitude of physical and environmental operating conditions, which individually or collectively influence the ability to achieve cathodic protection on the carrier pipe. For a given cased carrier system, operating parameters are subject to change both by design and from naturally occurring circumstances. A change in one parameter can and many times does change other parameters due to interactions among the significant factors. Throughout the history of the pipeline industry, pipeline owners have designed new cased carrier systems and altered, or opted not to alter, existing systems based primarily on their own experiences. Thus, for a given set of conditions, different owners have used different designs. This situation is most easily illustrated by the lack of consensus as to whether or not the casing should be electrically shorted to the carrier under any or all sets of conditions. These considerations prompted PRCI to initiate a study to determine the effectiveness of cathodic protection on simulated buried cased steel pipelines by systematic laboratory procedures and to incorporate the results into a form readily usable in the field.
Result: The objective of the program as originally conceived was: (a) Phase I, Determination of the effectiveness of cathodic protection on simulated buried cased steel pipelines by systematic laboratory experiments; (b) Phase II, Correlation of the laboratory data by computer modeling. Phase I was conducted as originally planned and amended to incorporate computerized analysis of the data. Because of the results of that analysis, the scope of Phase II was changed to the characterization and/or detection of carrier-to-casing electrical resistances.
Benefit: An industry recommended practice to determine the factors which are significant regarding the ability to achieve cathodic protection on a cased carrier and to establish the interactions between all factors for the proper design, installation and maintenance of cased carrier pipes.
