The Direct Integration Method: A Best Practice for Relief Valve Sizing
By Mark Siegal Consulting Engineer Silvan Larson and William Freivald Valdes Engineering Company |
What if someone were to tell you that there is one method available for sizing relief valves that applies to virtually every situation, including two-phase flow and supercritical fluids? And what if they told you that method is more accurate and easier to use than traditional methods or formulas? As it turns out, both of these statements are true. The approach described here — the Direct Integration Method — involves numerical integration of the isentropic nozzle equation [ 1].
Figure 1. Today, with the help of spreadsheet programs
and simulators, the once-cumbersome Direct Integration
Method is easier than ever to use to size relief valves
BS&B Safety Systems
From as early as 2005, the “method of choice” for determining the flow through a relief valve has been the Direct Integration Method [ 2]. API 520 has also sanctioned this method due to its general applicability to any situation where the fluid is homogeneous [ 1]. However, because this method is perceived to be difficult or time consuming, many engineers continue to opt for older, simplified methods, even though such methods can produce less-accurate results. For instance, without careful analysis, using…