Overview
Ashtead Technology was approached to support a project to connect an unmanned platform to the existing NGT 36″ pipeline by installing a new 20″ pipeline at a designated tie-in-point. This operation required the installation of two guide clamps, two support clamps and a hot tap clamp on a live 36″ pipeline. The project was carried out on a jack-up vessel in shallow water depths of 10-13 metres, with air divers performing the primary subsea work.
The NGT pipeline was protected with a 90mm concrete weight coating and an 18mm asphalt anti-corrosion undercoating. Because of the unique placement of the clamps, coating removal was necessary at three distinct points along the pipeline, each varying in length.
This challenging operation highlighted Ashtead Technology’s expertise in delivering tailored solutions for intricate subsea projects in demanding environments.
Solution
The initial phase of the project started by using 8″ and 6″ electric dredges to expose the sections of pipeline needed for the clamps. The dredging took around 38, uninterrupted hours in total.
Once the pipeline was exposed, the Coating Removal Tool (CRT) was deployed to strip away nearly 12 meters of concrete weight coating, which included a three-layer wire mesh. The CRT effectively broke the concrete into manageable shell sections for easy removal.
After removing the concrete, over 9 meters of the 18mm asphalt layer was cleared around the pipeline at the clamp locations.
The CRT is capable of cleaning an area of 1.5 meters before needing to be repositioned. To ensure thorough cleaning, the CRT made multiple movements, guaranteeing that no required section of the pipeline remained unclean, outperforming comparable technologies.
The steel surface was cleaned to an H.B2.5 finish, meeting the surface finish standards required for the hot tap clamp.
Benefits and value
In order to prove that the equipment was suited to the required work scope, Ashtead Technology carried out coating removal trials at its Inverurie facility using a test piece that matched the pipeline. These trials ensured the CRT fitted the pipeline’s concrete coating and optimised jetting settings for the offshore work. They also provided accurate timing estimates for removing both the concrete and asphalt coatings.
Using underwater cameras and real-time positioning tools, the team worked precisely and efficiently throughout the operation.
Thanks to thorough preparation and the use of specialised equipment, Ashtead Technology successfully completed the job safely, on time, and with minimal disruption to the live pipeline. This approach saved the client time and ensured the clamps were installed without issue.