ment for pipelines in the presence of “unmeasureable and unknowable” factors to “systematically and objectively capture everything that is known and use the information to make better decisions.”1 It is with this approach that the data described below have been collected and used as the basis for this report’s responses to the questions asked by Reclamation in the charge to the committee (see Chapter 1, the section entitled “Reclamation’s Request”).
The committee reviewed the available data on the performance of DIP with polyethylene encasement (PE) and cathodic protection (CP) to assess the observed range of material and pipeline system behavior in aggressive soils. As a comparison, the committee also reviewed the available information on the performance of DIP without PE or CP, DIP with PE and without CP, and DIP with CP and without PE, as these data might represent local behavior if local failure of PE or CP in a field system was the underlying cause of observed corrosion and/or pipeline failure. Information was also reviewed for comparison with bonded dielectric coatings on both steel and ductile iron water and sewer pipelines. An additional factor that may come into play in a failure of operating pipelines is the design and installation of other components into the pipeline system.
The committee was asked to use the failure data provided by the U.S. Department of Transportation’s (DOT’s) Office of Pipeline Safety (OPS) for operating steel pipelines with bonded coatings and CP as the benchmark standard for comparison with data on DIP with PE and CP. Therefore, problems with design and installation failures that lead to external corrosion must be considered as contributing factors to the performance of each system and cannot be discounted.
The following sections present the findings of the data review based on presentations made to the committee; on publicly available documents; and on specific information provided by the Bureau of Reclamation and utilities and on additional data provided by other sources at the request of the committee.
The obtained data on pipeline materials and operating pipelines fall into the following categories of data types. The data type classifications (1 through 5) are listed from the most quantitative to the most qualitative:
Data Type 1—Documented failures of operating pipelines due to external corrosion for pipelines of a given pipeline type, including pipe thickness, pipeline age, and soil condition. Such information can be converted into a linearized maximum pitting or corrosion rate for that specific failure (assuming that pitting begins upon pipe installation) and into a failure rate per mile per year if the total number of miles of pipeline of that particular age and soil condition are known.