Fitness for Service Assessment after Demethanizer Arbf Near Miss

On June 15^th, 2018 at the LyondellBasell Channelview OP1 olefins unit, a process upset in the chilling train led to temperatures colder than the Minimum Design Metal Temperature (MDMT) of the T-3601 Demethanizer Tower. A Level 3 Brittle Fracture Fitness for Service (FFS) assessment was performed to establish minimum allowable temperature (MAT) acceptance criteria based on fracture mechanics (API 579 Part 9, Level 2 methodology) and subsequent crack inspections were performed to validate assessment results. This paper will demonstrate the steps required to perform a level 3 FFS assessment and will show how process modeling tools can be used to estimate dynamic temperature changes when direct measurement is not available. Additionally, the hazard scenario in context of the Process Hazard Analysis will be reviewed along with proposed safeguards.