The mainline pipeline runs from northwest Alberta in Canada to the area of Chicago, Illinois in the United States. Numerous lateral pipelines from northeast British Columbia and northwest Alberta feed gas into the main pipeline. A computer analysis of the cathodic protection attenuation and voltage gradients was made. Rectifier and groundbed installations are to be located at compressor stations and main line block valve sites. Deep anode groundbeds are being used exclusively, so an analysis of subsurface geology was conducted. A computer analysis of AC induction was completed in areas where the pipeline parallels high voltage transmission lines.
The main pipeline runs 1,900 miles (3,050 kilometers) from northwest Alberta in Canada to the area of Chicago, Illinois in the United States. Designing cathodic protection for a long pipeline such as this involves many factors. A logical, step-by-step approach is essential to insure a successful design. The project was begun by making a route survey to determine soil conditions and sub-surface geology along the way. During this survey, the locations of other pipelines, DC current sources and electrical transmission lines were noted. The pipeline is located about 65 feet (20 meters) from a parallel foreign pipeline for most of the route. This required an analysis of the cathodic protection of both parties to determine the possibility of cathodic interference. In several areas in the United States and Canada, the pipeline parallels high voltage AC transmission lines, so safety concerns over induced voltages had to be addressed. Attenuation and voltage gradient calculations were made to determine rectifier spacing and the distance required between the pipeline and anode groundbeds. Right-of-way limitations and voltage gradient concerns dictated that deep anode groundbeds should be used for the mainline piping. These groundbeds have been located at compressor stations and main line block valve sites, yielding a spacing of about 20 miles (32 kilometers), which was commensurate with the data developed in the attenuation calculations
This paper describes the steps taken in preparing the design and discusses the fmal design characteristics. AC mitigation and safety practices are also included as are the corrosion control requirements for horizontal directional drilled river and highway crossings.
THE PIPELINE
Route of the Pipeline
The pipeline is owned and being built by a number of companies that have established both a Canadian and an American entity. Known as the Alliance Pipeline, it extends from Fort St. John, British Columbia to Chicago, Illinois. The Canadian portion of the mainline pipeline consists of 972 miles (1,565 kilometers of NPS 36-inch (914 ram) through NPS 42-inch (1,067 ram) diameter pipe, seven mainline compressor stations and seven possible future compressor stations. The Canadian portion also includes lateral pipelines totaling 479 miles (771 kilometers) of NPS 4-inch (114 ram) through NPS 24- inch (610 ram) diameter pipe with a large number of lateral compressor/meter stations. The U.S. portion of the mainline pipeline consists of 888 miles (1,449 kilometers) of36-inch (914 ram) diameter pipe, seven mainline compressor stations, seven possible future compressor stations, five delivery/meter stations and an NGL extraction plant. The overall project also includes a number of mainline and lateral block valves. The routing is shown in Figure 1. Pipeline Operation The pipeline is a high pressure transmission line. The 36-inch (914ram) main line carries natural gas at a pressure of 1740 psi (12 Mpa). Initial throughput is designed to be 1.325 billion cubic feet (37.5 million cubic meters) per day.
