ABSTRACT The paper discusses integrity management of pipelines in operation. Typically this involves identification of pipeline response and the potential risk for failure, e.g. excessive feed-in to lateral buckles, upheaval buckling, and dynamic behavior of free-spans. Identification and analysis of such response is not trivial, as large data sets from external surveys and operational data for large networks of pipelines in operation need to be processed. Often, history effects from previous surveys as well as input from Design need to be taken into account to obtain the full picture of the pipeline behavior. In this work, the integrity management engineer relies on the set of procedures for performing integrity assessment, combined with understanding of pipeline physics.
In order to improve pipeline integrity assessment process, an analysis tool for performing screening assessment of pipeline response is developed. This is a combined effort from Reinertsen AS and Statoil Transport Net. The software tool is developed in order to perform integrity assessment of pipelines in operation more effective, but without compromising the confidence of the results. The software processes spatial input from pipeline surveys i.e. cross-profile data, along with pipeline design data. This allows pipeline response to be assessed with reference in design or as-laid configuration. Changes in response may be monitored over time by comparing the response of multiple surveys in one analysis. After identification of potentially critical pipeline response, the pipeline load utilization can be assessed directly without performing time consuming FE analyses. Instead strain levels in both vertical and lateral planes are established from processing the survey data directly. This produces an instant evaluation of the bending utilization of the pipeline, and is referred to as strain screening.
The paper presents the theoretical background for the strain estimation methods. The application of the tool is illustrated though a case study for a 36" gas pipeline on the Norwegian shelf. Further, the paper discusses the confidence of the various strain screening methods and their range of application.