Coflexip and IFP are carrying out an extensive research and development program to investigate the behavior of aluminium alloys as a substitute for both carbon steel used in the armour layers and for the stainless steel internal carcass in order to reduce the weight of the flexible. The results obtained in laboratory tests on the feasibility of using aluminium alloys have been confirmed by nine months of testing on three prototypes immersed in the Mediterranean Sea. The use of aluminium permits a reduction in weight of up to 40 % as well as an increase in the laying depth.

1 Introduction

Due to the increasing depth of offshore oil and gas production it is necessary to reduce the weight or to increase the mechanical characteristics of the flexible risers and flowlines used to link subsea equipment to floating production units. Several solutions to this problem have been studied, namely the use of composite materials and aluminium alloys. Use of composite materials in the armours has been investigated and a flexible prototype of six hundred meters length has been immersed eighteen months ago in the Brazil sea and is still operating without any problem. This reduces the total weight of the pipe by 20% but increases the price compared to a conventional flexible. On the other hand, the use of aluminium alloys offers the advantages of even greater weight reduction because we can replace more steel than in the case of composites, easy formability and competitive price, but with some limitations in corrosion behavior and mechanical characteristics.

2. Coflexip flexible structure

1. an interlocked internal carcass. Its purpose is mainly to prevent collapse of the inner sheath should, by accident, the external sheath is torn out and external hydrostatic pressure applies directly onto the inner sheath.

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