Keywords: Fatigue Analysis; heat exchanger; cyclic thermal and pressure transients
We were requested by an international client to perform fatigue analysis for design life assessment on their heat exchanger coil – located within a fired heater in accordance with ASME Section VIII, Division 2, Part 5.
The heat exchanger is designed to heat natural gas for the regeneration of drying beds. The unit is exposed to cyclic thermal and pressure transients. The heat exchanger coil has been designed as a pressure vessel in accordance with AS1210-2010 and the connecting piping has been designed in accordance with AS4041-2006.
Thermal and stress analyses were performed on the unit in order to calculate design cycle life. The geometry of the unit and its operating cycles were provided by the client. The unit consists of a set of inlet and outlet manifolds with three independent tube passes carrying the process gas. There are thirty-six (36) 3532 mm-tubes and seventy 180-degree elbows in each tube pass.
Fins were placed around the upper twenty-seven tubes. Based on our review of the unit geometry and loading, only one of the passes needed to be modeled for analyses. All fins on the tube connecting to the outlet manifold were individually modeled. ANSYS finite element analysis software was used in all analyses.
The following loading conditions were considered in the structural analyses:
• Thermal Transient Plus Gravity
• Switching from Low to High Pressure plus Thermal Transient plus Gravity
• Switching from High to Low Pressure plus Thermal Transient plus Gravity
• Start up to Low Pressure
• Start up to High Pressure
We perform engineering design and analysis for clients in industries including manufacturing, petrochemical and energy.