Though I haven't yet got a chance to specify relief valve to a water line, I have seen/investigated openings and damages in condensate lines that are supposed to move water at elevated temperature and sometimes at higher pressure also. The releases are always 2-phase with partial steam and a water spray.  But the water temperatures were found around 130 F – 150 F.  Hence, I would expect a 2-phase release if the water temperature is substantially high, say around 130 F.  However, I would recommend you verify with Steam Table also to predict the situation.