Abstract As crude pipelines age, they are exposed to environmentally assisted failure mechanisms, with cracking being one of the most reported anomalies. With operating companies managing assets several decades beyond their design lives, the early detection and rigorous management of critical anomalies, including cracks and metal loss, have become fundamental to maintaining pipeline integrity. This study extensively addresses the pivotal challenges in managing crack and metal loss features on four Main Oil Lines (MOLs 1.1, 1.2, 3.4, and 3.5) commissioned between 1963 and 1973. One of the implemented methodologies was to collate and analyse all In-Line Inspection (ILI) data for the MOLS under study between 2015 and 2022. These data were obtained using Ultrasonic Crack Detection (UTCD) and Ultrasonic Corrosion Mapping (UCM) tools. In addition, Phased Array UT (PAUT) data used for the field verification of crack locations on MOLs 3.4 and 3.5 are discussed and documented. Furthermore, the study incorporated a comprehensive fitness-for-service (FFS) assessment performed on the respective MOLs to evaluate the failure potential of the cracks and metal-loss anomalies identified from ILI data at the maximum allowable operating pressure. Based on the ILI data, each crack field and crack-like defect was evaluated and classified into four categories (I, II, III, and IV) according to their tolerance to pressure and severity. Similarly, the metal loss features were assessed and ranked based on their criticality. Metallurgical investigations of cut samples from MOL 1.2 and 3.5 indicated that the pipe material composition lacked resistance to cracking mechanisms. The FFS assessment recommended several mitigation strategies, which are discussed in detail in this paper. As of 2023, over 1,000 crack defects and metal loss anomalies have been managed without any Loss of Primary Containment (LOPC), which is a testament to the success of the FFS-based management program. This study comprehensively explores life extension philosophies, detailing the repair methods, crack management methodologies, and monitoring strategies that have defined the service life extension of the pipelines under study, culminating in a strategic, long-term asset replacement plan.
Shaapera et al. (Mon,) studied this question.