Large-width/diameter riser segment lowerable through a rotary of a drilling rig

A riser segment assembly comprising:

• a first flange comprising:
• a first mating face configured to mate with an adjacent riser segment, a first end spaced apart from the first mating face, a first flange central lumen, and an auxiliary hole configured to receive an auxiliary line;
• a first main tube having a first main tube central lumen, a first end, and a second end;
• the first end of the first main tube welded or threaded to the first end of the first flange such that the first main tube central lumen is in fluid communication with the first flange central lumen;
• an isolation unit configured to seal an annulus in the riser segment assembly if a drill string is disposed in the riser segment assembly, the isolation unit comprising:
• a housing with a maximum transverse dimension, the housing further comprising:
• a first housing portion having a first housing portion central lumen, a flange surrounding the first housing portion central lumen, a first end, and a second end, the flange of the first housing portion defining a first recess extending radially inward from the maximum transverse dimension, the first end of the first housing portion welded or threaded to the second end of the first main tube such that the first housing portion central lumen is in fluid communication with the first main tube central lumen;
• a second housing portion having a second housing portion central lumen, a flange surrounding the second housing portion central lumen, a first end, and a second end, the flange of the second housing portion defining a second recess extending radially inward from the maximum transverse dimension, the first end of the second housing portion coupled to the second end of the first housing portion such that the second housing portion central lumen is in fluid communication with the first housing portion central lumen;
• where the first recess is aligned with the second recess to define a passage configured to receive within the maximum transverse dimension an auxiliary line passing through the flanges of the first and second housing portions;
• a second main tube having a second main tube central lumen, a first end, and a second end, the first end of the second main tube welded or threaded to the second end of second housing portion such that the second main tube central lumen is in fluid communication with the second housing portion central lumen;
• a second flange comprising:
• a second mating face configured to mate with an adjacent riser segment, a second end spaced apart from the second mating face, a second flange central lumen, and an auxiliary hole configured to receive an auxiliary line, the second end of the second flange welded or threaded to the second end of the second main tube such that the second flange central lumen is in fluid communication with the second main tube central lumen;
• and
• an auxiliary line having a first end coupled to the first flange, a second end coupled to the second flange, and a medial portion laterally offset from the first end of the first flange and the second end of the second flange and disposed in the passage.