In November 2000, gas build-up inside the confined compartment around an offshore platform caisson leg led to an explosion. The gas was found to be hydrogen generated by the depleted anodes inside the caisson leg. An investigation of the fatal explosion made several recommendations, including removal of the anodes, biocide-treated water and blasting grit that had accumulated inside the caisson legs over two decades.

A pilot study was conducted to evaluate the use of a vapor corrosion inhibitor (VCI) for structure integrity protection after removing the blasting grit and biocide-treated water from one of the legs. Treatment commenced with spraying the internal diameter of the leg with a water-based solution containing a vapor corrosion inhibitor with a biocidal treatment. This was followed by fogging the internals with an amine carboxylate VCI. Finally, a string of pouches containing VCI powder was suspended on hangers to assure continuous saturation of inhibitor in the space. Corrosion coupons were installed 6m below the manhole before closing it.

Results after one year and beyond were positive and the system was adopted for rectification of the problem.

Subject
Water, Piping, Inhibitor performance, Corrosion rate, Volatile corrosion inhibitors, Vapors, Amines, Inhibitor treatment, Carboxylates, Corrosion inhibitors, Powders, Corrosion protection, Corrosion coupons
Keywords:
offshore platform, caisson legs, vapor corrosion inhibitors, amine carboxylate, corrosion
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2014
Association for Materials Protection and Performance (AMPP)
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