Two phase PSV application is developed to accurately size the PSV orifice for the two phase sub cooled liquid according to the API 520. Two phase PSV sizing is a complex procedure requires careful attention while manipulating the governing equations and choosing initial conditions. Application is designed such that it guides the users to select right options based on the initial process inputs to accurately determine the required orifice size and PSV designation. Application warns the users for incorrect inputs and options selection. Application has a separate process input section, fluid inlet condition and fluid composition and characteristics section. Application wars the user about incorrect inputs and all possible errors. After providing correct inputs then by simply pressing ‘Calculate’ button all the required results are calculated and displayed in the result section.