(11b) Modeling Shell Side Pressure Profiles for Heat Exchanger Tube Rupture Scenarios

Shell and tube heat exchangers are commonly used in the oil, gas, chemical, and nuclear industries. One fault that may occur with heat exchangers is a tube rupture, an overpressure scenario in which high pressure fluid flows into the low pressure region. This overpressure event may compromise the mechanical integrity of the exchanger and can lead to the equipment’s failure. Significant property damage associated with tube ruptures have been documented in the past. To protect against such scenarios, overpressure protection measures such as relief devices are installed on the low pressure side of the exchanger. However, care has to be taken to accurately model the shell side pressure profile in order to avoid exceeding allowable design limits. To determine the size of the relief device that must be installed, API 521 recommends a dynamic analysis be performed when there are large differences in pressure between the shell and tube side. Using a time step-size of one millisecond, a dynamic analysis is performed on a liquid-liquid system and liquid-vapor system. The transient effects of the relief valve are taken into account. The challenges encountered in modeling these scenarios are addressed. This includes appropriate assumptions that can be made with minimal loss in accuracy. The effects of the pressure ratio and shell volume on the liquid-liquid and liquid-vapor systems pressure profiles are mentioned. Lastly, this paper also discusses ways of mitigating tube rupture consequences.