Heat exchanger for cooling cracked gas

A process for connecting an uncooled tube and a cooled tube of a heat exchanger for cooling cracked gas with a tube connection between the uncooled tube, the process comprising the steps of:

• clamping a weld pool backing ring, embedded in an insulating layer inserted in a cooling intermediate space of a gas inlet header, in contact with a tube inner surface of a tube outer part of the gas inlet header, in a device for preparing a weld seam connection from the gas inlet header to a water chamber;
• attaching the gas inlet header to the water chamber without air gap with contact of a gas inlet welding lip of the gas inlet header, at a ring-shaped end piece of the tube outer part of the gas inlet header, on an end face of the cooling intermediate space with a water chamber sealing lip, formed at a water chamber bottom end face of the water chamber located opposite the gas inlet welding lip;
• preparing a first welding layer with a metal active gas welding torch and with a metal active gas welding wire with a welding filler material for a root protection;
• mechanically removing weld slag formed on a top side of the first welding layer;
• and
• welding or filling a remaining weld seam with a welding material over the first welding layer in one pass in 2n welding layers or welding beads.

A heat exchanger for cooling cracked gas, the heat exchanger comprising:

• a cooled tube configured as a double tube comprising a cooled inner tube and a jacket tube, the cooled inner tube being enclosed by the jacket tube at a radial distance to form a tube intermediate space, through which a cooling medium flows;
• an uncooled tube;
• a tube connection between the uncooled tube and the cooled tube, the tube connection comprising:
• a water chamber having a water chamber end face and a water chamber bottom end face;
• a gas inlet header connected to the uncooled tube, the gas inlet header having a forked cross section and comprising a tube inner part and a tube outer part, defining a cooling intermediate space therebetween, and an insulating layer of a heat-insulating material in the cooling intermediate space, wherein the tube outer part is connected via the water chamber to the jacket tube, with the tube outer part connected to the water chamber end face and the tube inner part facing the water chamber bottom end face at an axial distance therefrom;
• and
• a ring configured as a weld pool backing ring arranged between an end face of the cooling intermediate space and the water chamber bottom end face and inserted into the insulating layer of the cooling intermediate space in a mounted turn-out or groove in the insulating layer on the end face of the cooling intermediate space, wherein the weld pool backing ring is in contact with a tubular inner surface of the tube outer part, the tube outer part comprising a tube outer part peripheral surface, the tubular inner surface and the weld pool backing ring being located radially inward of the tube outer part peripheral surface with respect to a longitudinal axis of the gas inlet header.