Offshore Platform Materials Integrity – Remediation Measures

Abstract

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