Page 379 - Pipelines and Risers

350 Chapter I8

18.5 Deepwater Pipeline Repair

18.5.1 General
In the last decade the world’s hydrocarbon industry has moved into deep waters and the
underwater pipeline repair technology is continuously developing to keep pace. In general, a
well proven capability exists to conduct repairs on pipelines up to a water depth of about 300
m, beyond which divers cannot realistically work in saturation. However, recently the use of
robotics has undergone significant advancement which together with experience gained in the
past few years in the field of pipe repair in deep waters (to 600 m) suggests that there is now
such a thing as deepwater pipeline repair technology, although improvements would be
necessary for specific scenarios.

Typically any deepwater repair procedure requiring the replacement of a pipe section will be
based on the concept of a spoolpiece installation using diverless mechanical connectors to
attach onto the free ends of the pipeline. End connector hardware capable of being installed
without divers has been developed by Hydrdtight of UK and HydroTech of USA. Refer to
vendor details contained in Attachments. The basic concept remains the same regardless of
whether divers are employed to carry them out as in more conventional repair operations
(refer to Figure 18.5). Unfortunately, the problems associated with physically accomplishing
each task as a diverless operation, remain significant.

Notwithstanding the above, there is a growing consensus that various ROV contractors could
collectively perform virtually all the tasks required with a minimum amount of special
support equipment having to be constructed.

This section outlines the progress made in the art of deepwater repair, presents guidelines for
new repair technology and discusses different ways to approach and solve a diverless repair
task.
18.5.2 Diverless Repair- Research and Development

Diverless repair systems had been considered since 1971 with two significant studies being
performed as Joint Industry Studies, one sponsored by Exxon Production Research and the
other by Shell. Aims of these studies were twofold; firstly to allow pipeline repairs at water
depths beyond diver capabilities and secondly to have a cost effective diverless repair system
that could compete with diver assisted repair systems. Some of the earlier studies were a little
too ambitious in that they attempted, optimistically, to solve all problems for both small and
large diameter pipe sizes and in water depths reaching 1300 m. As a result, although the
studies identified many of the major problem areas, they did not lead to the development of
actual repair capabilities since, at that point in time, the conclusions and recommendations
were considered to be either impractical or too expensive to implement. Also these earlier
studies were prompted by the industry anticipating in the very near future (at that time) the
need to repair large diameter, concrete coated pipelines in water depths to 1300 m. As we now
know, this did not materialize. This again contributed to the fact that the early studies did not
result in any repair system.