51314-4200-Protection of Caisson Legs with Vapor Corrosion Inhibitors - a Case Study

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Product Number: 51314-4200-SG

ISBN: 4200 2014 CP

Author: Usama Jacir

Publication Date: 2014

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A fatal accident occurred in November 2000 as a result of an explosion inside the confined compartment around the caisson leg “SB” of Power Generation Barge (PBG). The investigation following the incident identified several recommendations one of which was to remove the blasting grit inside the caisson legs that had accumulated over the last 20-25 years from blast cleaning operations. A pilot study was conducted to remove the blasting grit and biocide-treated water from one of the legs (PA at USAAP) to be maintained in an empty condition. The integrity of this structure was then preserved by the application of a regime of Vapor Corrosion Inhibitors (VCIs) coupled with the adoption a Corrosion Monitoring Program. A 3-phase corrosion control system was applied inside the leg. This consisted of first spraying the internal diameter of the leg with a water-based VCI solution containing a biocidal treatment. This was followed by fogging the inlet internals with an amine carboxylate VCI. Finally a string of breathable emitting devices containing VCI powder were suspended on hangers to assure continuous saturation of inhibitor in the space.Corrosion coupons were installed 6m below the manhole of the leg before closing it and after the final activity of the preservation. Results after one year and beyond were excellent and the system was adopted for rectification of the problem.