Splash zone repair

In the tidal zone and the spray zone (known as the splash zone), cathodic protection is generally not very effective. Here thick coatings or sheathing with corrosion-resistance materials (e.g., based on NiCu) are necessary to prevent corrosion attack [4]. The coatings are severely mechanically stressed and must be so formed that repair is possible even under spray conditions. Their stability against cathodic polarization (see Section 17.2), marine growths, UV rays and seawater must be ensured [4,5]. 

The difficulties of such operations on the research platform Nordsee are described in Ref. 9. The Murchison platform was provided with a combination of impressed current protection and galvanic anodes because there was a limit to the load to be transported [12]. The anodes for platforms are installed and provided with cables at the yard. They are installed with redundancy and excess capacity so that no repairs are necessary if there is a breakdown. The lower part of the platform up to the splash zone is usually placed in position in the designated location at least 1 year before the erection of the deck structure so that impressed current protection cannot initially be put in operation. This requires cathodic protection with galvanic anodes for this period. This also means that the impressed current protection is more expensive than the galvanic anodes. 

Figures 12.14—12.17 show applications of the ProAssure products. It can be seen that overwrap repairs can be successfully applied on the platform, in the splash zone as well as in the sea. Obviously the complexity increases as repairs move from dry to wet and subsea environments. This is not only restricted to application of the composite laminate but also to related activities such as removal of existing coatings and surface preparation, as well as additional requirements such as the need for scaffolding, absailers and/or a service barge. A similar scenario applies to the clamp repair solution, which is generally advantageous over the overwrap repair method in cases of deeper...

Figure 12.15 Repair installation at the splash zone of an offshore platform ex-factory rubbery-based coatings are prone to degradation over time in service and could be repaired with a system like ProAssure Wrap Extreme.

Leong, A.Yi., Leong, K.H., Tan, Y.C., Liew, P.F.M., Wood, C.D., Tian, W., Kozielski, K.A., 2011. Overwrap composite repairs for offshore risers at topside and splash zone. In 18th International Conference on Composite Materials, Korea. 

Field tests in the Florida Keys showed that the anodes retained physical integrity for at least 4.5 years. Laboratory test indicated that concrete resistivity does not represent a main limiting factor in performance of such anodes and that periodic water contact (as encountered in the splash/evaporation zone of marine bridge substructures) is actually necessary for long-term anode performance. This low-cost method is a competitive alternative to impressed current cathodic protection systems and a significant improvement over gunite repairs. SHRP-S-405, 10... 

Atmospheric testing techniques and standards described in Chapter 11 are applicable to the splash/spray and atmospheric zones. As indicated previously, these tests give useful information for the design of mcurine structures but in many cases, additional information on the performance of components and component interactions is needed. Full-scale or subscale testing usually is required for the adequate assessment of techniques and materials for maintenance and repair of marine structures. This testing is required not only to determine the performance of the systems but also to derive cost information applicable to the specific application. 

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