Abstract: In this process ethylene is prepared by pyrolytically cracking ethane in a pyrolytic cracking furnace having a plurality of elongated serpentine-situated thermal cracking tubes which have a longer run life as a result of the selective cracking of a C.sub.3 to C.sub.12 hydrocarbonaceous material at conditions sufficient to selectively place a coat of amorphous relatively smooth coat of coke on the interior walls of the thermal cracking tubes and thereby mask the catalytic effect of iron, nickel, both iron and nickel, or other metal catalytic sites indigenous to the walls of the furnished tubes. In this manner, the amount of cracking time realized for each particular furnace before regeneration of the same is increased by 20 to 50%.