Shut-in cryogenic liquid: a few kelvin of warming exceeds hose ratings, so a line whose only vent is a set of small orifices still needs a relief

Quick check for any cryogen line that is closed upstream (a facility valve) and vents downstream only through small orifices (an injector, a nozzle, a metering plate). With the orifices open, boil-off leaves at trivial back pressure. Example: about 3 g/s of oxygen vapour near 92 K through ~16 mm2 at Cd 0.7 needs only about 1.4 psi, so no relief seems necessary. But if the orifices block (ice from condensed water freezing during chilldown is a documented cause; NASA SP-8089, p. 41), the liquid is trapped at nearly constant volume. Liquid oxygen at its normal boiling density reaches ~1,000 psig after warming only about 3 K; liquid methane reaches ~1,200 psig after about 5.5 K (CoolProp: solve T at fixed density for the target pressure). That is above typical braided-hose working ratings. So fit one small cryogenic relief per line, set between the supply maximum and the lowest component rating, even when normal venting makes it look unnecessary. Adding any isolation valve on that side makes it mandatory.