Lift analysis for decommissioning

How can the Murchison offshore platform be dismantled safely and in stages? To gain insight into this, Iv performed lift analyses for various platform modules on behalf of Heerema Marine Contractors. Some modules were missing lifting points and main load-bearing beams due to these being removed during previous works. Iv was commissioned to design new lifting points (pad eyes) and examine the module’s structural safety during the lift.

Iv carried out detailed lift analyses, including the creation of a computational model of the main structure with the correct weights and centre of gravity. The stiffness of the cables and applicable offshore standards were also taken into account. The module’s weight and centre of gravity were determined by weight reconciliation based on a thorough offshore survey. Furthermore, Iv verified the required cables (slings), the hook capacity, and the shackles.

When designing the new lifting points, it was vital that they were placed in the correct location, taking into account the strength and stability of the structure, such as the columns and adjacent beams.

Although computers provide valuable insights, it is often essential to perform manual calculations to verify the local strength of the structure. This requires, among other things, a thorough knowledge of the platform’s history and previous structural adaptations. In particular, detailed structural drawings including welds, cross-sections and material types.

The collaboration between Heerema Marine Contractors and Iv has a long history. It allows us to benefit from each other’s expertise and skills, resulting in a safe and ‘fit for purpose’ outcome. As a result of this collaboration and thorough preparation, the Murchison platform could be safely removed with full assurance of structural safety.