Page 373 - Pipelines and Risers

344 Chapter 18

If concrete sleeves are utilized, the damaged concrete weight coating may be replaced in-situ.
Fabric sleeves, which are prefabricated, may be zipped and strapped around the damaged
section of pipe and subsequently pumped full of grout via the relevant facilities located on
board the surface vessel. Refer to Figure 18.1.

The sleeves may be manufactured to suit the pipe size and coating and provide sufficient
flexibility to adapt to uneven surfaces of the pipe. Typically, they may be provided in lengths
of up to 6 meters. The underside of the pipe has to be made accessible to enable the
installation of the sleeve. This option, may be used for local or one-off type repair, but is
expensive for more extensive repair requirements.

Znstallation of Engineered BackfZl
If this method is adopted, the engineered backfill material is positioned so as to bury
completely the damaged section of weight coating and thus provide the requisite protection
and stability. Refer to Figure 18.2.

Installation of Sand or Grout Bags
Sand or grout bags may be employed in a similar manner to the engineered backfill to provide
local cover and burial of the damaged section of the pipeline. Divers are used to place the
bags around the pipeline system. Refer to Figure 18.1. Comparatively the operation is more
labor intensive than a similar operation using engineered backfill hence, the financial
ramifications may be restrictive for extensive repairs to the pipeline weight coating.

Methods similar to these are frequently used as a integral part of localized span rectification.

Installation of Stabilization Mattresses or Weight Saddles
When this method is employed, flexible mattresses or concrete saddles are positioned over the
pipeline system to provide the required stability and protection. In each case the actual
positioning operation is usually completed using a subsea handling frame located over the
exposed pipeline. In general, the flexible mattresses are considered to be more suitable than
the concrete saddle due to their greater ability to adapt to transient seabed conditions. Refer to
Figure 18.3.

This option may be used for a considerable number of situations and provides a versatile
facility for one-off or the more extensive type of repair.