Effect of Pressure Loading on Integrity Management

Integrity assessment or life predictions for in-service pipelines are sensitive to the assumptions they rely upon. One significant source of uncertainty is the pipeline operating pressure data often captured and archived using a Supervisory Control and Data Acquisition (SCADA) system. SCADA systems may be programmed to collect and archive data differently from one pipeline to another and the resulting pressure records can be significantly different on the basis of the sampling techniques, data processing and the distance from pump and compressor stations. This paper illustrates some of the issues involved in pressure load characterization and is based upon work sponsored by the Pipeline Research Council International (PRCI). A series of sensitivity studies using fatigue crack growth calculations have been carried out to evaluate several factors that can influence crack stability and growth predictions that are often employed in pipeline integrity planning and repair programs. The results presented will highlight the issues related to performing integrity management based upon pump/compressor discharge or suction SCADA data to characterize the potential severity of pressure fluctuation or peak pressure dependent defects, illustrate the differences in fatigue crack growth rates along a pipeline segment and demonstrate the complexity of pressure cycle severity characterization, based upon distance from discharge, elevation, hydraulic gradient, for different sites along the pipeline route.