A pass or tube or a section thereof or “U” bend in a coil in a paraffin cracker having section having a pore size in the metal substrate from about 0.001 to 0.5 microns over coated with a dense metal membrane permits the permeation of one or more of H2, CH4, CO and CO2 from cracked gases moving the reaction equilibrium to the production of ethylene and reduces the load on the down-stream separation train of the steam cracker.