Structural Integrity Assessment of ERW Seam Flaws
Location
Structure Type
Software Used
Alberta, Canada
NPS Pipeline System
Abaqus, API 579-1/ASME FFS-1 Calculations
Objective
To define conservative flaw acceptance criteria for ERW seam flaws using API 579-based fracture assessment and validate findings through FEA. The goal was to support ILI data interpretation and provide a basis for integrity management of the pipeline system.
Model of crack-like flaw in Abaqus
Failure Assessment Diagram (FAD)
Challenges
The assessment faced challenges due to uncertainty in material properties near the seam weld, especially the potential for reduced toughness in localized areas. Limited test data required a conservative approach. The evaluation also had to define acceptable flaw sizes without considering long-term degradation like fatigue, pressure cycling, or hydrogen cracking. Modeling crack-like flaws under internal pressure was further complicated by variability across pipeline segments.
Solution
To overcome these challenges, a conservative fracture mechanics methodology was implemented in line with industry standards. Crack-like flaws were modeled as semi-elliptical surface defects using standardized geometry definitions. A conservative estimate of fracture toughness was applied to ensure safety margins were maintained. Both analytical and numerical approaches were used, including detailed Finite Element Analysis (FEA) to validate predictions and capture stress behavior around critical flaw scenarios. The combined approach ensured consistency, robustness, and traceability in the assessment of pipeline integrity.
Result
The results demonstrated that smaller flaw configurations could be tolerated under current operating conditions, while larger or deeper flaws posed greater integrity risks. The FEA results closely matched the analytical predictions, confirming the accuracy and reliability of the chosen methodology. Stress distribution patterns observed in the simulations reflected expected crack behavior, reinforcing confidence in the modeling approach. Overall, the study provided clear criteria for flaw acceptance and supported the safe interpretation of In-Line Inspection (ILI) data as part of a proactive pipeline integrity management program.
