How do you design a pipeline depressuring system and what are the critical considerations?

Design considerations: target pressure and time (typically to safe level within 15 minutes for fire scenario), minimum metal temperature during blowdown (Joule-Thomson cooling can cause brittle fracture), flare system capacity, liquid dropout and disposal, and blowdown valve sizing. Use transient simulation to model pressure/temperature profiles. Size orifices or valves for controlled rate that prevents excessive cooling. Material selection must handle minimum temperature. Segment long pipelines with intermediate valves. Consider automated blowdown for rapid response to fire detection.