Life Extension of Ageing FPSO and SPM Calm Buoy Hulls and Deck Plates Under Corrosion Effects - Part 1A

This study entails the understanding of surveillance data that determines mitigation strategies on ageing and structural health challenges on hull and deck plates which drives life extension decisions on floating assets. The reviews focussed on structural health issue such as corrosion wastage on floating facilities hull and deck plates. Thus, data gathering, their interpretations and managements were found useful towards life extension project delivery. It was observed that the number of new floating production storage and offloading (FPSO) and single point mooring calm buoy (SPM) built for support of various oilfield production and export operations will continue to increase while the existing ones is near the end or have exceeded the end of their design operational life. The study shows that floating facilities undergo four stages of degradation viz: initial, maturity, ageing and terminal stages. The menace of corrosion wastages was observed in this study as one of the long standing challenges encountered by FPSO and SPM calm buoy hulls and deck plates. It was observed that previous studies relied on data gathered from trading/shuttle tankers to carry out this study on FPSOs, while others rely on data obtained from laboratory in corrosion coupon. While FPSOs are stationed in an oilfield and hardly relocates during their service life, trading tankers moves from one region of the ocean to the other, thus exposing them to various sea state and varying corrosion conditions. On the other hand, data obtained from corrosion coupon in laboratory is under control while that obtained from an FPSO operational location is in real marine environment and represents the real state of corrosion wastages. Thus, corrosion data obtained from an FPSO/SPM calm buoy operational location in marine environment represents a more realistic data in marine corrosion wastage case studies. Therefore, it was observed that more case studies should be carried out on different floating assets in the areas of corrosion wastages. More so, the validity of data used for life extension studies were observed as 18 months by some class society, while some oil majors allow data taken within 5 years before the end of life, but such data must be subjected to review by a subject matter expert. Similarly, minimum of 5 gauging points per area of 1m2 deck plate strake or zone is required unless where there is marginal corrosion wastage that would require 8 gauging points.