Skene High Strength Repair of Carrier Pipe

North Sea, 2001

In 2001 FoundOcean’s services were required to repair damaged pipeline bundles in the North Sea. The cracking had occurred during installation, poor conditions at laydown of the towhead caused a buckle to occur in the line, which initiated the carrier pipe to crack.  Due to the project schedule, it was not possible to fabricate a replacement bundle. Thus, it was necessary to repair the damaged region to reinstate the integrity of the carrier pipe. FoundOcean provided the following tailor made set of unique solutions:

• Isolate by making a dam inside the carrier pipe, the region of the crack, so that the bundle could be grout filled.
• Install a split sleeve stress grouted clamp over the area of the crack.
• Grout fill the annulus between clamp and carrier pipe, post tension clamp bolts, thus making a new load path across the damaged region.

A high performance grout was required to achieve and exhibit high strength, good flow and low heat. In addition FoundOcean carried out trials, firstly to investigate and substantiate the means of creating a dam within the carrier pipe. Secondly the trails demonstrated our ability to grout effectively.

Trials were initiated to investigate the means of creating the dam. This involved selecting appropriate aggregates, investigating their physical properties, grain size, angle of repose, etc. and then establishing placing characteristics using a small hopper and test box.  From this, full size tests were undertaken, placing aggregates into an actual ‘bundle model’ to understand the particle flow and placing characteristics.

The bundle test rig comprised an 1155 OD x 9.0m long carrier pipe complete with all associated flow-lines, etc.  The ends of the carrier pipe were blanked off and inspection windows were provided to study the aggregate placement and grout filling.  Pipework ports for filling of the respective components were also provided.

From these tests it was determined that a pea shingle should be adopted because of its rounded particle flow characteristics, as well as being permeable to allow the free flow of water through it during the grouting phase.

Given that all the work was subsea, FoundOcean used additives to stabilise the grout mixture. This solution significantly reduced thermal stresses and cracking, extending divers working time.