The FCCU at BPCL MR commission in1984 produces valuable substances such as gasoline, butane, and propane. The unit features an RCC chimney designed to release flue gases at a height and velocity that maintains pollutant concentrations within acceptable limits. In 2017, during periodic structural assessment of the RCC stack, internal cracks were discovered in the extracted concrete cores. Over a year and a half, these cracks were closely monitored using non-destructive testing methods (USPV & RHT), revealing their active nature. Subsequent strategic testing involved various NDT techniques, discovering a significant 60% degradation in the characteristic strength of concrete (fck). Chemical tests and corrosion analysis revealed varying levels of deterioration, with chlorides dominating the outer face and carbonation affecting the inner face. Utilizing Computer Modeling (SAP 2000), a comprehensive assessment compared bending moment capacity and demand for different load combinations based on IS 4988:2015 standards. The findings indicated the stack is safe under dead load but revealed vulnerability to lateral load combinations. The paper delves into the degradation of concrete strength, the intrusion of chlorides causing re-bar corrosion, the methodology for strategic testing of stack, concrete analysis, and the retrofitting scheme designed to extend the structure's specific target life.
