A riser segment assembly comprising: - a main tube having a first end and a second end as well as a first portion and a second portion, wherein the main tube includes an isolation unit configured to substantially seal an annulus in the main tube if a drill string is disposed in the main tube; - a first flange and a second flange (112a, 112b) being coupled to the first end and the second end of the main tube, respectively, each flange comprising: a) a mating face configured to mate with a flange of an adjacent riser segment; b) a central lumen configured to be in fluid communication with the main tube; c) at least one auxiliary hole configured to receive an auxiliary line; d) a neck portion (248, 252) being welded to the first portion and the second portion of the main tube, respectively; - the auxiliary line extending between the first and second flanges (112a, 112b), the auxiliary line comprising: a) a first connector coupled to the first flange; b) a second connector coupled to the second flange; and c) a variable-length removable body having a first end configured to be connected to the first connector, and a second end configured to be connected to the second connector, wherein the removable body includes a medial portion that is laterally offset from the first and second ends (144, 148) of the removable body, the medial portion of the removable body being configured to extend around the isolation unit; wherein the isolation unit, includes: a) a first housing member welded to the first portion of the main tube and b) a second housing member welded to the second portion of the main tube, wherein the second housing member is connected to the first housing member, e.g. by bolts; wherein an outer diameter of the main tube in a region of the isolation unit is greater than an outer diameter of the flanges (112a, 112b). - a main tube having a first end and a second end as well as a first portion and a second portion, wherein the main tube includes an isolation unit configured to substantially seal an annulus in the main tube if a drill string is disposed in the main tube; - a first flange and a second flange (112a, 112b) being coupled to the first end and the second end of the main tube, respectively, each flange comprising: a) a mating face configured to mate with a flange of an adjacent riser segment; b) a central lumen configured to be in fluid communication with the main tube; c) at least one auxiliary hole configured to receive an auxiliary line; d) a neck portion (248, 252) being welded to the first portion and the second portion of the main tube, respectively; a) a mating face configured to mate with a flange of an adjacent riser segment; b) a central lumen configured to be in fluid communication with the main tube; c) at least one auxiliary hole configured to receive an auxiliary line; d) a neck portion (248, 252) being welded to the first portion and the second portion of the main tube, respectively; - the auxiliary line extending between the first and second flanges (112a, 112b), the auxiliary line comprising: a) a first connector coupled to the first flange; b) a second connector coupled to the second flange; and c) a variable-length removable body having a first end configured to be connected to the first connector, and a second end configured to be connected to the second connector, wherein the removable body includes a medial portion that is laterally offset from the first and second ends (144, 148) of the removable body, the medial portion of the removable body being configured to extend around the isolation unit; a) a first connector coupled to the first flange; b) a second connector coupled to the second flange; and c) a variable-length removable body having a first end configured to be connected to the first connector, and a second end configured to be connected to the second connector, wherein the removable body includes a medial portion that is laterally offset from the first and second ends (144, 148) of the removable body, the medial portion of the removable body being configured to extend around the isolation unit; a) a first housing member welded to the first portion of the main tube and b) a second housing member welded to the second portion of the main tube, wherein the second housing member is connected to the first housing member, e.g. by bolts;