Structural Integrity Assessment of a Sour Service Low Pressure Production Trap Using Fitness-for- Service Methodology

This paper presents a real case study of a structural integrity assessment of a Low-Pressure Production Trap (LPPT) at a Gas Oil Separation Plant using Fitness-for-Service methodology. The equipment, constructed from carbon steel (CS A-516 Gr. 65) with a nominal wall thickness of 18.0 mm, operates in a sour environment prone to hydrogen-induced cracking (HIC) and step-wise cracking. Automated ultrasonic testing revealed HIC and inclusions at depths ranging from 7.3 mm to 14.8 mm, with step-wise cracks up to 2.2 mm in height. Fitness-for-Service assessments, using API-579 Level 1 and 2, confirmed the equipment’s fitness for continued service, provided regular monitoring and protective measures are implemented. This study underscores the utility of Fitness-for-Service in extending the lifecycle of aging infrastructure while ensuring operational safety.