Earlier post “Criteria for Requirement of Pressure Relief Device for Tube Rupture” has discussed the criteria for determination of creditability of tube rupture in heat exchanger. For a particular scenario where a Pressure Relief Device (PRD) is required to protect a heat exchanger from tube rupture, there is still issue on the type of PRD to be used.
It is always recommended to provide a Pressure Relief Valve (PRV) to minimize inventory lost to flare and drain disposal system. For a heat exchanger with gas in low design pressure (LPS) side, whenever tube rupture occurred, the gas may provide some “cushion” effect to minimize surge pressure. Thus, a pressure relief valve (PSV) is acceptable in this case.
However, in the event liquid in LPS side, sudden tube rupture may generate a huge surge pressure to the LPS within a mili-second and results the intermittent peak pressure exceeded design pressure of LPS, pressure relief valve (PRV) is NOT recommended in this case. Pressure relief valve is known to be a “slow acting device”, it may NOT response fast enough to relieve pressure. Thus, a rupture disk which known as “quick acting device” is always recommended in this case.Nevertheless, there are some researches carried out by HSE UK and reported that there are rupture disks may NOT open quick enough as compare to the surge pressure built-up. Details may refer to :
- Testing and analysis of relief device opening times
- Examination of the effect of relief device opening times on the transient pressures developed within liquid filled shells
Per API STD 521 (2007), section 5.19.3, one-dimensional dynamic modeling / analysis is recommended where there is a wide difference in design pressure between HPS and LPS (e.g. 70 barg and above). A one-dimensional dynamic model is to simulate the pressure profile and pressure transients developed in the exchanger from the time of the rupture which includes tube-rupture fluid dynamic and Pressure relief device response.
Related Topic
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