Application of Risk-Based Inspection Frameworks to Gas Transmission Pipelines in the South West Zone

Risk-based inspection (RBI) frameworks offer a systematic methodology for optimising inspection resource allocation in gas transmission pipeline systems by focusing inspection effort on the highest-risk segments. This study applies an RBI framework to a section of the gas transmission pipeline network in the South West geopolitical zone, specifically the West African Gas Pipeline (WAGP) onshore segment and the Oben-Ajao trunk line. The research employs the American Petroleum Institute (API) 581 risk-based inspection methodology, adapted for Nigerian pipeline conditions, to calculate probability of failure (PoF) and consequence of failure (CoF) scores for individual pipeline segments. Input data for the assessment include pipeline age, material grade, operating pressure, soil corrosivity data, coating condition records, cathodic protection performance data, and historical incident records. The study produces a risk ranking matrix for the assessed pipeline network and derives an optimised inspection programme prioritising high-risk segments for immediate in-line inspection (smart pigging) and intermediate-risk segments for accelerated above-ground survey programmes. Findings reveal that 18 percent of the assessed pipeline segments fall into the high-risk category, accounting for 74 percent of the total estimated failure consequence exposure. Recommendations include immediate smart pig runs on the identified high-risk segments, development of a dynamic RBI data management system, and mandatory RBI methodology adoption for all gas transmission pipelines above 12-inch diameter operating in Nigeria. Keywords: risk-based inspection, gas pipeline, API 581, South West Nigeria, pipeline integrity.