QRA and Reliability Optimization in Gas Pipeline Construction using Fault Tree Analysis A Scenario-Based Construction-Phase Risk Assessment Framework

Gas pipeline construction comprises route preparation, excavation or horizontal directional drilling (HDD), pipe transportation and stringing, lifting, welding, non-destructive testing, coating, lowering-in, backfilling, testing and tie-in activities. These operations may interact with existing buried utilities and live hydrocarbon systems, creating pathways to pipeline damage, loss of containment, fire, explosion and struck-by injury. This study develops a construction-phase risk assessment framework that integrates task-based hazard identification and risk assessment (HIRARC), Fault Tree Analysis (FTA), data-screened Quantitative Risk Assessment (QRA), and reliability improvement. Four top-event scenarios are formulated: (i) mechanical damage to an existing buried gas pipeline during excavation; (ii) fire or explosion during hot work; (iii) unexpected hydrocarbon release during construction or tie-in; and (iv) a dropped pipe or load striking a person during lifting. Preliminary fault trees separate initiating mechanisms, failed safeguards and exposure conditions, thereby clarifying the AND/OR relationships that must be validated. Documentary triangulation uses the supplied project report, relevant accident-investigation records, and technical guidance on FTA, excavation and hot-work controls. The industrial visit to Oil Terminal is treated only as contextual familiarisation; the visit photographs do not demonstrate the occurrence of any modelled event. The analysis identifies utility-location assurance, permit-to-dig, positive isolation, gas testing, hot-work control, lifting integrity, exclusion zones and communication as critical barrier themes. Since task-specific failure rates, exposure denominators and consequence parameters were not supplied, numerical probabilities, risk contours and risk-reduction percentages are intentionally not reported. The principal contribution is a transparent, auditable framework for validating construction-related fault trees and populating a QRA when reliable project data become available.