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Existing industry standards have established the compressive strain capacity of pipelines within an empirical basis. The compressive strain capacity is generally associated with the peak moment. This approach has evolved from elastic stability concepts used in structural engineering for unrestrained pipe segments subject to primary loading (i.e. force or load control) conditions. This limiting condition does not take advantage of the observed performance for buried pipelines, when subjected to displacement control events such as differential ground movement, where the pipe curvature can exceed the peak moment response without loss of pressure containment integrity. This inherent conservatism may have a negative impact on project economics or sanction where the compressive strain capacity, rather than tensile rupture limits, governs the strain based design methodology. For these conditions, alternative performance limits defining the pipe compressive strain capacity are required. A numerical study was conducted, using finite element methods, to examine possible alternative compressive strain criteria for use in strain-based design applications. The results from this study and the requirements to bring these concepts forward through integration with industry recommended practice are presented.

This paper describes the application of “digital pigging” procedures for converting field measurements of pipeline geometry (e.g., top of pipe survey profiles), results from geometry pig surveys, or analytically generated pipeline centerline profiles into corresponding profiles of pipeline curvature and bending strain. Application of digital pigging procedures to pipeline elevation and/or inclination profiles developed from accelerometer based geometry pigs provides a basis for performing the additional calculations required to develop bending strain profiles which may not be a part of the geometry survey deliverable but are required for pipeline structural integrity evaluations. This paper presents examples of digital pig runs over analytical pipe centerline profiles to illustrate the important effects of feature length, pig length and curvature gage length. Comparisons of the results from digital pig runs over actual geometry pig data profiles and digital pig runs over the corresponding known analytical profiles will illustrate how basic pattern recognition concepts can be used as a basis for improved synthesis of real pig data signatures. This paper also presents examples of digital pigging calculations performed on geometry pig survey data that show how low-pass filtering can be used to reduce the effects of noise in the survey data as well as the influence of curvature gage length on the computed curvature/bending strain profiles.

Two offshore development projects which involve subsea arctic pipelines are being proposed by British Petroleum Exploration (BP). Both projects are located in the central Beaufort Sea, offshore the North Slope of Alaska. The Northstar Development Project pipeline is located on State of Alaska submerged lands (Ref. 1). The Liberty Development Project pipeline is located on both State of Alaska submerged lands and the Federal Outer Continental Shelf (OCS) (Ref. 2). The State of Alaska has been conducting an ongoing technical review of the Northstar pipeline Right-of-Way (ROW) application over the last 30 months. The Liberty pipeline is in the preliminary engineering design stage. This paper reviews the engineering approaches being considered to accommodate unique arctic conditions, with emphasis on ice gouging and strudel scour and permafrost. The major environmental issues associated with a subsea arctic pipeline, including oil spill detection, will also be reviewed. The paper will focus on the regulatory aspects of the pipeline and ROW, rather than the design specifications of the pipeline itself. Introduction The Northstar Development Project (NDP) is located approximately 21 miles northwest of Deadhorse, Alaska, in 39 feet of water. Oil will be produced from an offshore man-made gravel island, processed to sales quality and transported through the Northstar pipeline. A utility pipeline is also proposed to be constructed within the same ROW. The offshore segment of the pipelines will be 6 miles. The pipeline route will be almost directly due south from the production island, will cross between offshore barrier islands and make landfall at Point Storkersen. The onshore portion of the oil pipeline would continue south and connect with the Trans Alaska Pipeline System (TAPS), Pump Station One. Alternative routes for the onshore portion of the utility pipeline to potential injection gas sources are being evaluated. Figure 1 is a map locating the Northstar project and proposed pipeline route(s). The Liberty Development Project (LDP) is located about 20 miles to the northeast of Deadhorse, in 22 feet of water. Similar to Northstar, the LDP proposes an oil sales pipeline and a smaller utility line within the same ROW. The offshore segment of the Liberty pipeline will also be about 6 miles long: about 1.5 miles on the Federal OCS and about 4.5 miles on State of Alaska submerged lands. The applicants preferred offshore route is south-southwest of the production island, with a landfall m the central Foggy Island Bay area, and about two miles west of the Kadleroshilik River. The onshore segment of the pipeline will tie-in to another new onshore pipeline currently being constructed for BP's Badami Development Project, approximately 14 miles east of Liberty. Figure 2 is a map locating the Liberty Development Project and proposed pipeline route. The two projects share a number of similarities. Both projects propose to use a man-made gravel island production platform, with stand-alone processing facilities. They also propose to install the pipeline(s) during the winter season using conventional earth-moving equipment operating from the sea ice surface; pipeline(s) will be laid in a trench and buried. The shore approach for both projects also involve burying the pipeline(s) some distance inland, then bring them above ground through a purpose-built gravel pad.