Which codes you're interested in depends on where you are and what you're protecting.
In the US & Canada, relief valves requirements for pressure vessels are addressed in ASME Section VIII, Div 1, UG-125 thru UG-136. Some PSV vendors will provide references to code requirements, Crosby, for example, publishes the relevant sections of Section VIII in their 'Crosby Engineering Handbook' for relief valve sizing, you can find it online at
The thing to watch there is their latest edition includes exerpts from ASME 1992 edition (2000 is the latest, I think - there might have been a 2002 edition by now as well).
Relief valve requirements for piping systems are covered in the relevant ANSI B31 codes, i.e. B31.3 for process piping (I've never dealt with the other piping codes, I'm assuming they'll have their own considerations). B31.3 section 322.6 covers relief valve requirements, and with a few additions largely just refers to the ASME Section VIII code paragraphs.
If you're in Canada, rules are pretty much the same, CSA B51-03, which covers pressure vessels, piping & boilers in Canada is largely an overlay spec that reiterates Section VIII and B31.3.
as refeerred earlier crosby egg hand book gives the formulae related to capacity and other requirements , pressure set point and type of media ad all other calculations depending on the pressure vessel design
In addition to the valves, one also needs to become aware of the design requirement for sizing and locating the inlet and outlet piping of the relief valves, and also the circumstances for which one must calculate a relief flow. In additon to the non-mnadatory appendices of the referenced codes, there are also paragraphs in the body of the code that definew when one must provide a relief valve, and those circumstances for which alternative safety provisions are permitted. Again, it is a function of which specific code is being met.
