Applied Methodology for the Execution of a Corrosion Risk Assessment & Risk Based Inspection (RBI) for Topside Facilities in Corrosion Resistant Alloys

DP3 and DP4 platforms of Bouri Oil Field are located in the Offshore Libyan Mediterranean Sea and are operated by Mellitah Oil & Gas B.V. Libyan Branch. In 2016, a project was established with the purpose to extend the life span of the production facilities which were approaching the end of their original design life. The study is intended to assess integrity of topside facilities and the impact of the corrosion to develop robust Risk Based Inspection program without impacting reliability and maintainability of existing facilities. A customized methodology has been developed and adopted to carry out the corrosion risk assessment of the topside pressure piping and equipment and the most relevant features of the adopted procedure are described in the paper. Given the great number of items involved in the assessment, the study developed an item categorization based on corrosion loops. Other hot topics addressed by the assessment were the definition of known corrosion issues, lesson learnt from field operations and the assessment of the effectiveness of the corrosion control measures in place. As the topside facilities are mostly made of corrosion resistant alloys (CRAs), simple but knowledgeable rules have been developed to assess the corrosion status of CRAs components after more than 30 years of operation. In addition, the available abundant inspection data have been collected and used to validate and amend both the applied rules and the corrosion predictive models applied for corrosion rate calculations. On the basis of the DNV RP G101 standard, the development of an effective and customized inspection plan was based on the output of the risk ranking process of the topside facilities pressure and piping components interrelated to the corrosion risk assessment as well as on a careful assessment of the past inspection’s records of each item. Criteria for the inspections and most adequate non-destructive techniques (NDT) selected for each vessel and group of piping are discussed as well in the paper.