Abstract

In order to enhance competitiveness of rigid risers for the Brazilian pre-salt, great effort has been devoted to study the feasibility of Steel Catenary Risers (SCR) directly connected to Floating Production Storage and Offloading (FPSO) units, where cost savings are expected from the reduction of pipe buoyance modules and overall piping length. A recent paper presented the technical feasibility of Damped SCR, which is a new SCR concept. In that study, some non-field-proven fatigue performance improvements were required, such as girth welds for mechanically lined pipe (MLP) with increased fatigue strength and/or upset end pipes. During the development of this technology, a fracture mechanics approach became essential for the assessment of fatigue and fracture limit state in order to guarantee that the risks associated with fabrication and inspection are within acceptable safety levels. This paper presents the main issues related to fabrication and inspection activities with a particular focus on the smallest critical flaw size. A semi-deterministic Engineering Critical Assessment (ECA) was performed as part of the conceptual design. The uncertainties about input data are discussed and a simplified procedure is proposed. Results are compared with relevant non-destructive testing reliability statistics. This study indicates that the benefits obtained from the use of materials with superior fatigue resistance are limited to the non-destructive testing reliability at some degree. As the proposed methodology deals with uncertainty in input data, a roadmap for the development of a full probabilistic risk assessment of fabrication and inspection feasibility at early design stages is devised.

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