Flange Leak Investigation on Kettle Heat Exchanger Operating at Low-Temperature Condition

Abstract

A kettle-type evaporator heat exchanger (TEMA BKU) is utilized to cool natural gas on the tube side from −34 °C to −55 °C, using Multi-component Refrigerant (MCR) as the cooling medium on the shell side. During operation, the heat exchanger encountered recurrent leakage issues at the channel-tubesheet bolted flange joint, particularly during the cooling down process. The primary objective of this research is to identify the causes of leakage and to propose viable solutions for minimizing the risk of leakage. To achieve this, Finite Element Method (FEM) was employed as an investigative tool to analyze the mechanical factors contributing to leakage. Results from the FEM investigation indicate that the leakage in the bolted joint of the heat exchanger is attributed to reduce of gasket seating stress as an effect of bolts self-loosening, influenced by several factors such as bolts plastic deformation, flange stiffness characteristics, and uneven temperature distribution. The study also reveals that gasket seating stress decreases after each shutdown compared to the previous start-up due to plastic deformation on bolts and flange gasket surfaces after shutdown. The findings of this study provide critical insights into the mechanical behavior of bolted flange joints in heat exchangers and offer guidance for their improved design and maintenance, enhancing operational reliability.