Since 1993, Devonport Management Limited (DML) has been developing techniques for strengthening, modifyirrg and repairing existing steel structures using composite materials. Composites were first used for such applications in the defence industry where a number of successful warship strengthening and repair projects were carried out. In developing techniques for use to the offshore industry much importance. was placed on the development of in-situ application methods that did not require special environmental controls or process equipment, A further consideration was to validate the performs of both the composite materials and modified structures in order to demonstrate the suitability of the composite reinforcement to regulatory and certifyin authorities. The first major offshore project has now been completed successfully turn this has led to the creation of a Joint Industry Product to widen the range of situations where composites can he considered for strengthening, modification and repair (SMR) such structures. This paper presents the background to the requirement for SMR, explains the advantages of composites, provides some case study information and describes the joint industry initiative to widen the use composites in SMR.
There are now almost 250 offshore installations in the UK waters. The average age of these structures is more than 15 years. Many of the structures are reaching the end of their original design life.
Improved hydrocarbon recovery, the need reduce costs by utilising existing infrastructure in the development of new fields, and the need to re-consider the adequacy of existing structures during the preparation of the safety cases which was required for every UK installation following the Piper Alpha disaster, have led to a requirement for strengthening, modification and repair (SMR) of existing installations to:
epair damage (fatigue or corrosion) to existing structures to allow the life of an installation to be extended.
Modify (which might include repair and strengthening of the existing structure and the addition of new structure existing structures to allow the incorporation of new equipment.
Strengthen existing structure to cater for additional load cases that have been identified during the preparation of the safety case e.g. blast loads.
The usual methods available to carry out such work have been strengthening using welding or bolting, Recently, however, composite materials have been used for such work. The composite materials are usually based on one or more types of carbon fibre either an epoxy or a vinylester resin. Trials programmes have been completed successfully for two operators, whilst one major offshore strengthening project has now been successfully completed. A Joint Industry Project (JIP), jointly undertaken by DML and MSL Engineering Limited, is now underway with the aims to develop materials data, validated design tools and a Design Guide to allow wider use of composites in offshore applications.
The composite materials, which have led to their selection for the above projects and to the JIP initiative, compared with more traditional SMR methods, are initially discussed below.
