Retrofits - Subsequent revisions to structures
Sometimes it needs an update. It does not matter if it was wrong or requirements have changed. But what matters is the way the retrofit is planned.
Because offshore working hours are expensive a retrofit requires perfect preparation. Avoiding hot applications, evaluate existing tolerances and having mockups are also important steps to a successful retrofit.
One example may be the additional fixation of grating. A common recurring problem is underestimating the power of wave run up. Not only by the maximum wave but also by regular waves. Although these don‘t deliver such maximum peaks as extreme waves, they still have enough power for a regular grating fixation to fail. Intermediate platforms that are missing such a design are regular subject to missing gratings.
In a recent project we investigated the actual performance of Hilti grating supports on behalf of our clients. The advantage of these grating anchors is that they are easily applicable to an existing structure. However, the disadvantage is the relatively low load-bearing capacity. We were able to improve one early failure mode and with the increased capacity we have identified a sufficient number of fixations. Since then no further missing grating have been reported.
Another example is the replacement of a handrail to enable walkable access from the ship via a gangway to the main access platform of a wind turbine. The task of OWT in this project included the structural review of the platform in order to absorb the shock load of the ship's walk-to-work system. Furthermore we designed the railing itself. It was important to use existing supports including managing its tolerances. OWT participated in the mockup tests at a local steel yard which improved perfomance of the gate.
The railing has been exchanged without reporting any difficulties which eventually lead to minimum costs for this measure.