Complex sentence: Although the Interprovincial crude oil pipeline (now part of Enbridge Inc.) has been the longest oil pipeline in the world since it was first constructed, until the completion of the TransCanada gas pipeline it was also the longest pipeline in the world.
Split into simpler sentences: Although the Interprovincial crude oil pipeline (now part of Enbridge Inc.) has been the longest oil pipeline in the world since it was first constructed. Until the completion of the TransCanada gas pipeline, it was also the longest pipeline in the world.