The objective of this paper is to provide operators of floating production systems that utilise dynamic flexible risers an opportunity to review the technology and procedures adopted by PGS Production. These procedures were utilised in order to verify/re-use the damaged/seawater annulus flooded Banff risers. Most of these risers were also classified as being safety critical. The scope of the work carried out covers the development of a seawater displacement treatment system using an inhibitor fluid. The feasibility and efficacy of the flushing treatment were rigorously developed based on hydraulic test analysis using sections taken from an actual flexible riser. An extensive corrosion fatigue-testing programme using seawater/CO2/inhibitor was carried out to establish optimal safe service lives for the “damaged and treated” case for these risers. This paper presents the successful results from this work covering the development of the remedial treatment process and the resulting corrosion fatigue work that has been conducted.

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Offshore oil and gas production environments provide severe challenges in terms of materials selection and dayto-day operations. Several issues encountered during commissioning of a North Sea platform and the remedial actions are presented. Iron contamination from debris generated during topsides construction and chlorides from the marine atmosphere provided the conditions necessary for ferric chloride pitting corrosion of uncoated 316 stainless steel (SS), duplex and super duplex SS, and 6%Mo SS pipework and vessels. Several offshore cleaning/coating methods were evaluated and a new procedure for cleaning was identified that achieved the desired goal without removal of metal or affecting the corrosion resistant alloy's passive film integrity. Corrosion protection of carbon steel bolting by encapsulation was employed to stop deterioration of an improperly applied anodic coating. Insulated SS instrument tubing was susceptible to crevice corrosion and chloride stress corrosion cracking (Cl-SCC) under wet insulation at the temperatures generated by the heat tracing. Solutions were suggested to minimize such forms of corrosion. Coatings exceeding the manufacturer's recommended thickness had been applied to several high temperature vessels and pipework to prevent SCC as well as ferric chloride pitting. The potential for coating disbondment at elevated temperatures due to high dry film thickness was evaluated through a testing program and onsite inspections. NomenclatureCl-SCC Chloride stress corrosion cracking CRA Corrosion resistant alloy CUI Corrosion under insulation DFT Dry film thickness SS Stainless steel