DNV Developing New Recommended Practice for Deepwater Pipeline Repair

DNV is to develop new specifications for remotely operated subsea pipeline repair in cooperation with an industry consortium. The consortium met today at DNV's headquarters for a kick-off meeting, and a new DNV Recommended Practice will be issued by the end of 2006.

The opening and sealing of existing deepwater pipelines pose a range of challenges, such as fully mechanised repair work beyond human diving depths, pipelines normally not being prepared for mechanical attachments, with no flanges or hubs to mate with, or pipe walls having limited strength, which may impose limitations on the attachment.

A DNV Recommended Practice that will be a part of the OS-F101 "Submarine Pipeline Systems" will be issued in 2006, providing acceptance criteria and state-of-the-art documentation of proven technology and sound engineering practices. The Recommended Practice will focus on prioritized issues identified by the industry. "One of this project's main challenges is to prepare a level technical basis for specifications, design and acceptance criteria and testing," says DNV's project manager Tore Mellem.

Back in 1998, DNV managed a similar project called "Mechanical Pipeline Couplings". This led to a Recommended Practice document relating to the development of a remotely operated pipeline repair and tie-in system for a full range of pipeline dimensions, including pipelines below diving depth. However, some aspects of that document, as well as the need to also cover clamps, plugs, hot-tap and welded sleeves, called for a new revision, and work has today been started to meet this need.

The technical areas to be covered by this project are:

  • installation and operational loads and temperature effects
  • the resistance to leaks of mechanical seals
  • the strength resistance of mechanical grips and welded connections
  • the criteria for fully mechanized hyperbaric welds
  • material factors for hyperbaric welds
  • the hydrogen induced stress corrosion cracking aspects will be coordinated with ongoing projects
  • the extent of qualification and monitoring during subsea operations to replace non-destructive examination.

Participants are BSPC/Gazprom, Dong, ENI Gas&Power, Medgaz, Hydro, Shell Norway and Statoil. DNV's knowledge and experience combined with that of these partners will ensure a reliable, practical and user-friendly Recommended Practice.

"This team will provide a good basis for acceptance throughout the industry of the new Recommended Practice, which will be practical, useful and adoptable," says Tore Mellem.