Tyra jacket readiness scope

Engineered solution for successful offshore campaign.


As part of the Tyra Redevelopment project, 6 existing jacket structures were to be reused in the redeveloped field configuration. The existing topsides and MSF structures were removed during summer 2020 and in connection with the reediness campaign preparatory work Subsea and above water tasks was planned to be performed during this Readiness Campaign on the platforms TEE & TWE.  Total awarded the entire campaign to BOSKALIS and BOSKALIS awarded the scope above water to SubC.

SubC’s scope of work

SubC’s scope was to solve the challenge of getting access to the jacket constructions where the Topside already was removed. Boskalis was suppling the vessel with a walk to work system and the entire campaign both subsea and above was to the executed from this vessel with required a smooth cooperation between SubC and Boskalis to ensure the best possible planning between diving operations and construction work above water.

At TWE, the task was to install a J Tube support brace which SubC had previously manufactured for TOTAL.

To enable the installation, we have designed, engineered, and manufactured an access platform that ensured access from the ship's W2W system. To reduce offshore duration, we thought innovatively and suggested the customer to design a stair tower with extendable wings that ensured access to the locations on the “legs”, which were to be welded in connection with the installation of the support.

This way, we saved the customer 7-8 days of offshore operation as the amount of scaffolding was greatly reduced. In addition, the platform for lifting and rigging the J-Tube support brace worked as predicted.

At TEE, we designed, engineered, and manufactured two access platforms so that a platform could be installed on each side of the jacket construction. We connected the two platforms with one of SubC's aluminum gangways to ensure flexibility and to ensure that work could be switched between the two sides of the jacket construction. The platforms were also designed to lift fenders and supports that had to be removed in the splash zone and under water. Our task generally consisted of devising the solution, designing, engineering, and manufacturing as well as preparing the script/workplan for offshore execution (Method description, lifting plans and installation procedure). SubC’s scope of work included fabrication and installation of new risers, a 13-meter-long J-tube support brace and fenders. 

Prior to the fabrication and installation phase, SubC was responsible for the preparation including project management, engineering, and development of the entire method statement.

Preparation and engineering phase

The preparation and engineering phase included the following:

  • Ensure a safe working environment
  • Establishing access to TWE and establishing any temporary hang off systems required for the installation
  • Define installation procedure for installation of the brace including welding to the existing jacket
  • All welding to be in compliance with MOTS-12, MOTS-31 and MOTS-33 in accordance with detailed design of J-tube support brace
  • Reporting

SubC was to design and engineer a solution on how to gain access from a vessel with a walk-to-work system to an offshore jacket structure without topside. The operation was carried out with innovative engineering: A customized staircase with adjustable wings and temporary access deck was the solution.

Pre-fabrication phase

The installation activities included the following:

  • Prior installation of new riser on row B on TEE, 2 existing fenders are to be removed
  • On TEE a submerged riser guard on row A were removed as it was no longer effective and cracks were developed in the connections to the existing structure
  • Fabrication and securing for sea transportation

Installation phase

The scope for the riser platforms is split into a mandatory part, enabling the riser and J-tube installation; and a series of optional scopes:

  • Mobilization of qualified personnel to perform the work on the “platform” 
  • Mobilization of required tools and equipment to perform the work on the platform
  • Mobilization of contingency tools and equipment to perform the work
  • Interfacing with the client and third party while on the platform to perform the work
  • Provide all necessary input for the required working permits to do the work
  • Supervise, communicate, and operate the 13-meter-long J-tubes support brace installation scope
  • Perform the J-tubes support brace installation scope according to approved procedures including welding to the existing jacket
  • Demobilization of personnel and equipment

Successful offshore operation

Perfect weather conditions ensured that the entire campaign went as scheduled.

The customized stairway with adjustable wings, and the temporary access deck were successfully installed and including the welding prior the fabrication and installation phase has been executed without any recordable incidents.