The problem

Our client had identified an area of internal corrosion inside a riser bend within the platform topsides. It was identified that a fully pressure-retaining welded steel sleeve repair was required to contain the corroded region, for which a bespoke design was required.

The solution

Jee first completed a definition phase to establish a number of key criteria, including preferred construction materials and welding philosophy, stand-off within the sleeve and a schedule for the repair. The definition accounted for pipeline contents, weldability issues and future integrity management requirements.

Following the definition phase, Jee completed the detailed design of the welded repair sleeve, including final materials selection, static stress analysis of the sleeve using ABAQUS FE methods, and fatigue assessment of the sleeve when subject to varying operational loads.

An assessment was also completed for the rest of the riser to review the effect of the sleeve on the original riser due to the additional mass and stiffness of the bend. Variations in the load seen at riser supports were identified.

Jee created the procurement and fabrication packages, including fabrication drawings, as well as material and coating specifications. Jee also carried out the offshore site-survey to finalise key dimensional parameters to allow the onshore fabrication to be completed.

The benefits

Jee provided a highly tailored solution focussed on a robust solution and future integrity of the riser, whilst working in close collaboration with the client.

Jee’s experienced team of design engineers have expert knowledge of detailed design and offshore fabrication, but also work closely with Jee’s integrity management engineers on a daily basis. This gave them the required understanding of the full-lifecycle issues that needed to be addressed for the design of this safety critical repair.

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