Jacket Repair

Client:
Operator
Year:
2019
Business Unit:
Consultancy

Our client approached us with two structural issues to their jacket and asked for a tight turnaround period.

A weld defect between two jacket members was noted during a subsea inspection campaign and cracks were then revealed on the brace side of the weld during another inspection.

Apollo was able to address the issue by coming up with a ‘more efficient way to do things’ and a quick turnaround. Concept designs were finalized within 3 months.  Detailed design was finalised within 4 months thereafter.

Apollo worked alongside the client throughout the development of the designs due to the complexity of the existing structure, fabrication, and installation requirements typical of clamp design scopes, with good feedback throughout the scope.

The Problem

  • A weld defect between two jacket members was noted during a subsea inspection campaign and then cracks were then revealed on the brace side of the weld during another inspection

The Solution

  • To ensure that these defects did not affect the integrity of the jacket structure, the following repairs were to be fabricated and installed:
    • Tie-rod assembly between horizontal jacket members
    • Repair clamp assembly between horizontal member 2H2 and diagonal member 2D4

And for all you engineers who want more details:

The background

A weld defect between two jacket members was noted during a subsea inspection campaign in 2017.  Cracks were subsequently revealed on the brace side of the weld during an inspection in 2019.

To ensure that these defects do not affect the integrity of the jacket structure, the following repairs were to be fabricated and installed:

  1. Tie-rod assembly between horizontal jacket members
  2. Repair clamp assembly between horizontal member and diagonal member

Apollo was initially asked to carry out the concept engineering of a new repair clamp for a member in collaboration with the SIM model holder.  The client preference was to have a clamp designed to resist the full in-place loading at the cracked connection.

Following an initial assessment of loads by the SIM model holder, a concept “fixed” clamp design was considered impractical to pursue due to concerns regarding the size of the clamps, fabrication and installation complexity, and bolt pretension required.

A concept “slip” clamp was proposed to reflect the functional requirements of the repair.  As part of the solution, a tie-rod assembly was designed (adopted from a similar previous solution) to induce a compression force into the horizontal member.  This repair concept has been taken into detailed design.

The solution

Apollo delivered a Basis of Design document, a concept design report, and 2 detailed design reports composed of 7 calculation packages for the design of the friction clamp, slip clamp, clamp connecting member, tie-rod clamps, and associated anodes.  24 detailed design drawings have been created on final delivery.

The solution was designed to meet several conditions run by the SIM model holder.  The main repair clamp was modelled against a photogrammetry scan to ensure all existing obstructions are accounted for.  Discussions were also carried out with the subsea installation contractor to develop a feasible installation sequence.  The collaborations have resulted in the design of a functional repair solution.

What did the client think?

We worked alongside the client throughout the development of the designs due to the complexity of the existing structure, fabrication, and installation requirements typical of clamp design scopes. The client was delighted with our approach to not just look to fix the problem but to complement the work already undertaken by their team. As a client who had primarily used Apollo across other disciplines, this was a great scope to work on and they were very impressed.

If you have a pressing issue and need engineering support, let us know on consultancy@apollo-oe.com

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