Hydrocarbon feedstock containing resid is cracked by a process comprising: (a) heating the hydrocarbon feedstock; (b) mixing the heated hydrocarbon feedstock with steam and optionally water to form a mixture stream; (c) introducing the mixture stream to a flash/separation apparatus to form i) a vapor phase at its dew point which partially cracks and loses/or heat causing a temperature decrease and partial condensation of the vapor phase in the absence of added heat to provide coke precursors existing as uncoalesced condensate, and ii) a liquid phase; (d) removing the vapor phase as overhead and the liquid phase as bottoms from the flash/separation apparatus; (e) treating the overhead by contacting with a hydrocarbon-containing nucleating liquid substantially free of resid and comprising components boiling at a temperature of at least about 260° C. (500° F.) under conditions sufficient to at least partially coalesce the coke precursors to provide coke precursor liquid, in the form of hydrocarbon droplets or a continuous hydrocarbon liquid phase; (f) collecting and removing the droplets; (g) directing the treated overhead from which the droplets are removed, to a heater to provide a heated vapor phase; (h) cracking the heated vapor phase in a radiant section of a pyrolysis furnace to produce an effluent comprising olefins, the pyrolysis furnace comprising a radiant section and a convection section; and (i) quenching the effluent and recovering cracked product therefrom. An apparatus for carrying out the process is also provided.