Abstract

The paper describes activities and critical issues in relation to the preparations, qualifications, reeling and installation of two 10" Steel Catenary Risers (SCR's) on behalf of Petrobras on the Roncador field, offshore Brazil, in 1360 m of water.

A combined installation technique with J-lay of the critical touchdown area and traditional reeling for the remaining flowline/riser part was applied. The operations related to reeling the pipe sections onto the reel, reeling off, welding on site (J-lay sections) and transfer to P-36 have been outlined. The paper describes in more detail the analyses performed to evaluate the effects of using the reeling method for installation of the risers. The following issues are addressed: riser torsional effects due to residual curvature, effects of residual stresses, ovalisation, strain concentrations, variability in yield strength, riser analyses, reeling analyses, fatigue aspects, hoop buckling and propagating buckling.

Introduction

SCR's have proven feasible for use on floating production facilities and should be regarded as competitive and alternative in relation to the flexible pipe market. Petrobras pioneered when they installed (J-lay) the 10" SCR for their P- 18 unit in 910 m of water on the Marlim Field, offshore Brazil in 1998. This was followed up by the successful installation of the two 10" (oil & gas) SCR's on the Roncador Field (P-36) in 1360 m of water, first quarter 2000. A so-called hybrid (patent by Petrobras) method was applied using both J-lay and Reellay.

During the last years, research has been performed by some installation companies with the objective of looking into the feasibility of full Reel-lay SCR installation. The main goal of this research has been to ensure that the reeling, unreeling and straightening operations would not jeopardise the fatigue life of the SCR's. This paper briefly describes the activities in relation to the Roncador SCR installation. Further details may be found in Ref. 1 and Ref. 2. Some of the relevant technical "issues" in relation to SCR Reeling and J-lay installation are described herein. The machining of pipe ends to reduce stress concentration in welds was one of the issues which needed some more evaluations in relation to the reeling process and in-place behaviour.

System Description

The two 10" flowlines to be connected to the risers had been pre-installed a year before the P-36 was installed. The flowlines were terminated approximately 2 km away from the planned platform position. This was to allow space for the installation vessel to recover the pipeline after the platform was in place without a risk of buckling the pipeline in the sagbend.

The riser pipes were standard API X-60 10" pipe with a nominal wall thickness of 20.6mm. The design life of the risers was 25 years. The pipes were coated with 2.8 mm thick three layer polyethylene coating, except for the upper 8 joints which were coated with 8mm thick anti-fouling coating. The total length of each of the risers from hang-off down to the tiein point to the flowlines was 2790 meters with only a few meters difference between the two risers.

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