Objective
Development of new design technologies for submarine pipelines laid on very uneven sea bottoms.
In particular the project deals with :
- Investigation on the state of the art in the field of submarine pipeline design.
- Assessment of new reliability based design criteria.
- Updating of knowledges on the dynamic behaviour of multispans and generally of free spans in the proximity of uneven sea bottoms and exposed to the action of sea currents.
- Design of a system for the monitoring of submarine pipelines laying operations.
- Design by the usual methods and criteria of a submarine pipeline laid on uneven sea bottom and, as a comparison, execution of the same design applying the new methods and criteria.
In the framework of phase 0 concerning the development of new submarine pipelines design methods and techniques the following problems have been dealt with :
- philosophy and methodologies for intervention works
- fatigue life of submarine pipelines
- elastoplastic behaviour of submarine pipelines
- pipelines interaction with active-mobile seabeds
- slope stability in underwater environment.
A state of the art has been porduced for each problem area.
The experimental tests carried out in Phase 1 have shown that :
- the static configuration achieved by the pipeline on the seabed affects the structural response amplitude due to the in-line vortex shedding
- in-line oscillations due to vortex shedding are a rare event which is likely to occur only in rather particular conditions, low turbulence and/or little deflected pipe
- the cross-flow response of the pipe is also function of the seabed geometry especially in the presence of sand-waves.
A computer program has been developed whichis capable of analyzing the dynamic behaviour on the bottom of sealines configurations featured by the presence of adjacent spanning sections.
The design criteria developed in Phase 2 are based on a reliability approach, applied to the following limit states:
- serviceability limit state
- buckling and collapse limit state
- fracture limit state
- fatigue limit state
- overload limit state
Tha analysis carried out has allowed to assess new partial safety factors for each limit state, the demonstrating that the design methodologies applied at present are rather conservative as the mechanical characteristics inherent in the structure are not exploited at their best.
A computer program for real-time monitoring during submarine pipelines laying operations has been developed in phase 3.
The use of this program on board the lay barge allows to monitor the laying variables in a much more rational and effective manner as for the static configuration taken by the pipe on the actual sea bottom.
On the basis of the results of Phase 2, in Phase 4 a new design methodology for pipeline wall thickness selection was developed and applied to a N.D. 20" submarine pipeline. The results demonstrated the cost effectiveness obtained by using the new design criteria and monitoring system as regards :
- cost of the materials
- cost of interventions
- cost of laying operations.
The exploitation of offshore oil fields in increasingly critical areas has involved the unavoidable necessity of facing the problem of sealines laying in uneven sea bottoms.
The project is therefore aimed at formulating new design criteria allowing to exploit at the very best the strength of materials. These criteria are based, among other things, on advanced knowledges on the free span dynamics acquired during the development of this project through experimental laboratory tests.
Besides, dealing with the problem of installing the sealines in critical areas the project carries out the basic hardware/software design for a sealine laying monitoring system so as to enhance the laying capability of the means used as well as the operations safety.
The project includes 5 phases:
Phase 0 : Critical review of design criteria, analysis, methods and techniques so far adopted.
This phase analyzes the state of the art concerning criteria and techniques for design and construction of submarine pipelines. The phase being also the preliminary activity for the development of the subsequent steps.
Phase 1 : Dynamic behaviour of adjacent spans.
This phase singles out a dynamic behaviour model for single spans and multispans, in the proximity of uneven sea bottoms, exposed to hydrodynamics actions and develops a procedure for the fatigue analysis of the spanning sections. Moreover this phase envisages experimental laboratory tests on free spans oscillation phenomena when exposed to sea currents in the proximity of the sea bottom.
Phase 2 : Advanced design criteria.
This phase develops a reliability based procedure aimed at finding out new advanced design criteria and new safety factors, taking into account different structural limit states.
Phase 3 : Sealine laying monitoring system.
This phase consists of the basic design of an integrated hardware/software system for real-time data acquisition and processing in order to support both the operator and the supervisor during laying operations.
Phase 4 : Advanced construction solutions.
This phase consists of the design of a N.D. 20" submarine pipeline laid on an uneven sea bottom using traditional methods and techniques and the new methods singled out during the previous phases.
The phase includes a technical economical comparison between the two solutions.
Programme(s)
Topic(s)
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DEM - Demonstration contractsCoordinator
20097 SAN DONATO MILANESE
Italy