By: Ian Smith, Senior Consulting Engineer, Quest Integrity
As seen in the December 2014 issue of Pipelines International. View the PDF version.
Quest Integrity used its InVista™ technology to provide both a metal-loss and geometry inspection of the pipeline, and various dents and ovalities were identified and quantified. Based upon their size, 16 of these geometric anomalies did not meet common depth-based acceptance criteria, and therefore required investigation and remediation.
The client wanted to perform an advanced assessment to investigate the lifecycle of the anomalies and establish a risk-based programme, since using depth alone is not an effective criterion for prioritising anomalies.
Quest Integrity performed remaining-life assessments on the dents and ovalities using the detailed geometry profiles that the in-line inspection (ILI) data provided. Understanding that geometry anomalies are prone to developing cracks, the probability of failure of a dent is related to the amount of time to crack formation. This time can vary widely between anomalies, and is based on the sharpness of the profile and the amount of pressure cycling that occurs.
Only three anomalies had a calculated remaining life of less than 100 years. The client scheduled digs for these three locations and has the advanced engineering assessment documentation to support the remainder of the geometry anomalies.
TWO KEY BENEFITS OF USING ADVANCED TECHNOLOGY TO ASSESS PIPELINE ANOMALIES
1. Better understanding of risk: Leveraging ILI data benefited the client with fitness-for-service knowledge. In this case, the geometry profile coupled with operating pressure data predicted the life cycle of the dents and ovalities and provided a remaining-life assessment.
2. Prioritisation of anomaly investigations: The remaining-life assessment of the anomalies provided a defensible rationale for investigating the ones with shorter remaining-life predictions. This decreased the number of digs from 16 to three, providing cost and time savings to the client.
Figure 1. InVista inspection data showing 2D axial and cross-section views of 9.8 per cent deep dent.
Figure 2. InVista inspection data showing 2D axial and cross-section views of 26.6 per cent deep ovality.
Figure 3. A finite-element analysis model of a dent showing axial stress due to pressure-thrust load.