Fracture Mechanics Based Remaining Life Assessment of Cracked Pressure Vessels in Nigerian Chemical Processing Facilities

This study develops and validates a fracture mechanics-based remaining life assessment (RLA) methodology for pressure vessels with detected planar defects in Nigerian chemical processing facilities, contributing an original Nigerian-context framework calibrated to local material properties, flaw sizing capabilities, and operating conditions. Fitness-for-service (FFS) assessment of cracked pressure vessels is internationally governed by API 579-1/ASME FFS-1 and BS 7910, yet their application in Nigeria is hampered by the absence of material fracture toughness databases and validated crack sizing data representative of local vessels. The study is structured in three components. First, fracture toughness (KIC and CTOD) and fatigue crack growth rate (da/dN versus delta K) testing is conducted on samples extracted from in-service AISI 516 Grade 70 pressure vessels from plants in Lagos and Port Harcourt. Second, phased array ultrasonic testing (PAUT) is performed on in-service vessels with documented planar flaws, and UT sizing accuracy is quantified against reference flaws introduced in vessel mock-ups. Third, a Level 2 API 579 crack-like flaw assessment is applied to the detected flaws using measured fracture toughness and refined UT flaw dimensions, and remaining life predictions are compared with observed crack growth from successive inspection intervals. The study provides an original validated RLA framework for Nigerian pressure vessel operators. Keywords: fracture mechanics, remaining life assessment, pressure vessel, API 579, fatigue crack growth.