A method is provided for manufacturing during which a first duct section is formed with a tubular first sidewall. A first opening extends through the tubular first sidewall. The forming of the first duct section includes disposing a first woven fiber sleeve over a first mandrel and disposing a polymer material with the first woven fiber sleeve. A second duct section is disposed with a tubular second sidewall. The forming of the second duct section includes disposing a second woven fiber sleeve over a second mandrel and disposing the polymer material with the second woven fiber sleeve. The second duct section is arranged with the first duct section. The second duct section engages the tubular first sidewall. The tubular second sidewall is located at and extends circumferentially around the first opening. A duct structure is formed by attaching the second duct section to the first duct section.

When manufacturing a pipeline that carries an array of electrical cables, insulation resistance monitoring is performed by a monitoring unit that is connected to the cables of the array and is mounted to a leading end of the pipeline. The monitoring unit tests the cables cyclically in succession. Monitoring is performed on the cables after their application to the pipeline and while the pipeline and the cables advance together through further manufacturing processes, such as insertion of the pipeline into the outer pipe of a pipe-in-pipe structure. If a fault is detected in any of the cables, an alert can be raised quickly enough to stop the process and to rectify the fault before the fault is covered and rendered inaccessible. The pipeline and the cables can advance continuously unless a fault is detected.