This paper explores the various degradation mechanisms experienced by a refinery’s RFCC catalyst cooler aeration piping system. A detailed analysis of the most recent failure and a past failure was conducted to determine the various metallurgical and mechanical degradation mechanism(s) that led to these failures. The analysis which covered both the old UNS S30409, TP304H stainless steel, and newly upgraded UNS S34709, TP347H stainless steel catalyst cooler aeration piping system, with the same design, showed the dominant degradation mechanisms to be low cycle thermal fatigue and low cycle fatigue-creep for the TP304H and TP347H stainless steel aeration system’s header and sub header. The TP304H aeration system failed after three years in-service and the TP347H aeration system after six months in-service. The proposed solutions to prevent recurrence include a design change of the aeration piping system, stricter quality control during fabrication, installation of liquid knock-out drums to prevent water ingress resulting in thermo-mechanical strains and a return to the TP304H metallurgy for the aeration system pending a detailed investigation into the TP347H failure.
The paper also explores the technical reason(s) for the metallurgy upgrade from TP304H to TP347H and how this change affected the aeration piping’s service life.
Key words: Intergranular Cracking, Plastic Strains, Mechanical Vibration, Low Cycle Thermal Fatigue, Low Cycle Fatigue-Creep, Polythionic Stress Corrosion Cracking, Stress Relaxation Cracking, Residue Fluid Catalytic Cracker.