I need to find where the ASME code says (in so many words) a relief device's set pressure cannot exceed the design pressure of a system's component with the lowest design pressure. Naturally, this is common sense, but it must be written somewhere. It should be in ASME Code Sect VIII, but it would help if someone had a citation from ASME B31.1 or B31.3, too.

I should add I am trying to protect a piping system, in this case. I have an expansion joint as my weakest link; hence, it de-rates the overall system by default. But, I really need something to cite...even if it appears in API as a best practice.

CuriousGeorge,

API RP 520 PI - Ed 7 - Jan 2000 RP, section 3.5.2 and Figure 1—Pressure-Level Relationships for Pressure Relief Valves, may give you some guideline.

Thanks! I was going to add that someone might know where I can find similar guidelines to cite, such as in an API Guideline or other industry accepted standard.

Please see attached from B31.3

Regards