This paper presents a case study of a hypothetical pipeline that operated without coatings or Cathodic Protection (CP) for nearly the first 20 years of its service. Metal loss anomalies with depths greater than 50% of nominal wall thickness will require excavation according to federal regulations. To reduce the number of unnecessary excavations, laboratory testing data combined with methodology from both API 579 and ASME B31.4 was applied to determine an optimized wall thickness (t').
Based on hypothetical anomaly data considered in this paper, the optimized wall thickness resulted in a 70% reduction in the number of anomalies that required excavation, while still maintaining a safety factor of 1.39 (corresponding to 100% SMYS). This ensured that the anomalies that posed an imminent threat were targeted, excavated and repaired.
Following the good engineering practices specified in ASME and API codes, tempered by engineering judgement and some conservative assumptions, the optimized wall thickness will result not just in cost savings, but also in repairing anomalies that constitute a substantial risk to public safety.