Walker Technical
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40" Seawater Caisson

 
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Overview

A 40” Caisson on a North Sea asset had sustained external corrosion resulting on several through wall defects in two separate areas.

Scope

The scope of work was to provide an engineered composite repair with a 10 year design life. This required Technowrap Rope Access Technicians working in the splashzone applying the Technowrap Splashzone repair system over the two areas. The two areas to be repaired both measured approximately 3m in length. The design conditions were;

Design pressure (bar) - 1.1bar
Design temperature (°C) - 20°C
Repair lifetime (years) - 10 years
Axial load (kN) - 30.2
Surface preparation - ST3

Challenges

On closer inspection, the hole on the lower part of the caisson was larger than reported. The original design was amended to incorporate the increased actual on –site defect size. Following this inspection, further holes ranging from 50mm – 400mm in size were identified along the caisson and required filling and profiling before the repair could be applied .

Solution

Before any surface preparation could take place it was necessary to ensure the through wall defects were sealed. To do this, a Technowrap composite plate was pre fabricated and then placed over the defect to seal the hole. The plate was held in place with Technoseal UW putty and ratchet straps. Once the putty was fully cured the application of the composite wrap began.

8 layers of Technowrap Splashzone repair system were applied. Walker Technical worked with the asset integrity team who provided surface preparation to ST3 cleanliness as per the engineered design calculations. Following unavoidable delays, the repair was completed guaranteeing the caisson with an extended life for 10 years.