Seamless pipe which forms the principal conduit of the riser joint. EXAMPLE The riser pipe is the conduit for containing the production fluid flow from the well to the surface tree.
Source: API RP 17G, Recommended Practice for Completion/Workover Risers, Second Edition, July 2006 (Reaffirmed April 2011). Global Standards
Seamless or electric-welded pipe that forms the principal conduit of the riser joint. NOTE The riser main tube is the conduit for guiding the drillstring and containing the return fluid flow from the well.
Source: ISO 13624-1:2009, Petroleum and natural gas industries – Drilling and production equipment – Part 1:Design and operation of marine drilling riser equipment. Global Standards