THE UTILIZATION OF A PIPELINE INTEGRITY MANAGEMENT SYSTEM FOR ECDA MANAGEMENT WITHIN GASUNIE

摘要

Gasunie has utilized External Corrosion Direct Assessment (ECDA) as proposed by the NACE as a valuable method to assess the corrosion threat to unpiggable pipelines. In addition, a new probabilistic methodology has been adopted to quantify the results of an ECDA and to account for any uncertainties experienced throughout the process. This approach, based on Structural Reliability Analysis (SRA) and Bayesian statistics, uses the data gathered in the pre-assessment to calculate a failure frequency for each ECDA region defined. In the indirect inspections step, the method allows automatic updating of the expected number of both coating and corrosion defects based on the results of two aboveground surveys (one for the detection of each). In the direct examinations step, the method uses the results from excavations to automatically update the performance characteristics of the survey techniques (e.g. probabililty of detection and probability of false indication), the time of initiation of corrosion defects, the defect depth, corrosion growth rate and several other relevant parameters. The failure frequency is updated accordingly. If desired, this updating can be performed after each excavation, until the failure frequency is sufficiently low. This allows the integrity manager to minimize the total number of excavations and thus reduce the overall cost of the ECDA process. Finally, in the post-assessment step a reassessment interval is calculated for the pipeline under investigation. In 2007 Gasunie has implemented the abovementioned methodology as part of its pipeline integrity management system, PiMSIider. The DA module has now become an integral part of the system, thereby enabling highly accurate, reproducible and time saving integrity analyses of the Gasunie grid. The DA module will be described in this paper by using an example of a part of a Gasunie pipeline that has recently been subjected to ECDA.