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ECNDT 2006 - Tu.1.5.2

Use of New Inspection Techniques to Evaluate Turrets Defects

Ricardo DE OLIVEIRA CARNEVAL, Sérgio DAMASCENO SOARES, Petrobras, Rio de Janeiro, Brazil Manfred RONALD RITCHER, Lucivaldo BRILHANTE, Petrobras, S. J. dos Campos, Brazil

Abstract. Cargo ships used on production and storage of oil, known as FPSO, have an important structure called turret. Turrets are responsible not only by ship mooring but also by keeping ship direction aligned with environmental loads and by fueling ship tanks. Turret welds defects obviously drawback ship integrity.

During service inspection of some FPSO turrets welds fabrication discontinuities are detected. Be-cause of detected discontinuities relevance and difficulties of ships docking to repair the defects an engineering critical assessment (ECA) has been done to study the possibility of avoid repair.

This paper presents the new NDT used on the discontinuities existent in FPSO turret welds.

Introduction

During normal service inspection (UT and MPI) cracks are detected on turret welds from two FPSO (Floating, Production, Storage and Offloading) ships (figures 1 e 2). Based on the big amount of crack detected mainly in high welds (00 and 01 joints, figure 3), operational people decided to re-inspect the welds. In some cases re-inspection pointed to crack increasing. Preliminary fracture mechanics studies and crack increasing suspects recommended the application of more sensible non destructive techniques to obtain a more reliable engineering evaluation.

The following, so called, “new” NDT have been used: ACFM, TOFD and Phased Array.

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