Authority reserve the right to ask for calculation for thermal relief. If you or your company have done sufficient research and can be submitted to authority as supporting document, then don’t waste your time to calculate it. Otherwise, you better get ready when authority ask for it…
In many event, a simple and smallest PSV i.e. DN 20 × DN 25 (NPS ¾ × NPS 1) would be sufficient for thermal relief.
Somehow if there is doubt the provided PSV is not adequate, it shall be calculated according to using Hydraulic expansion method may be used.
If the liquid being relieved potentially flash or form solids while it passes through the PSV, hydraulic expansion with two phase relief method may be used. Details refer to :
- J. C. LEUNG, “Size Safety Relief Valves for Flashing Liquids”, Chemical Engineering Progress, February 1992, pp. 70-75
- J. C. LEUNG, and F. N. NAZARIO, “Two-Phase Flashing Flow Methods and Comparison”, Journal of Loss Prevention Process Industries, Volume 3, Number 2, 1990, pp. 253-260
- L. L. SIMPSON, “Estimate Two-Phase Flow in Safety Devices”, Chemical Engineering, August 1991, pp. 98-102