EnginSoft - Conference Abstracts

EnginSoft Users' Meeting 2008
Le Tecnologie CAE nell'Industria

FEM Analyses of offshore pipelines during pressure test - multi-objective optimization

Marchionni Lorenzo - Saipem Energy Services
Vitali Luigino - Saipem Energy Services

Abstract

Offshore pipelines are generally subject to lateral and upheaval buckling instability under operating conditions due to internal pressure loads and thermal expansion.

In addition, deep water offshore pipelines can be subject to lateral buckling during system pressure test caused by the high compressive loads applied on the steel during installation and high internal pressure applied during the system pressure test.

The lateral buckling is a complex problem with a lot of related parameters and is very time expensive to perform a reverse engineering activity well knowing the history load but without to have exact informations about soil properties affecting pipe-soil non-linear resistance forces one of the main parameters governs the actual behaviour of offshore pipelines under lateral buckling.

This paper refers to the experience on an offshore pipeline laid in deep water and experiencing lateral buckling during the system pressure test.

The multi-objective optimisation was used to obtain the best value combination of the un-known relevant parameters. ModeFrontier (v. 4.0.2) has been used to perform the optimisation process.

In this paper, the following is discussed:

• Brief description of the phenomenon;
  
• Description of the FE model to simulate the pipeline response during system pressure test and operating conditions;
  
• Selection of the un-known relevant parameters and of design targets: relevant parameters are related to the pipe-soil resistance force, while design targets are related to the pipe configuration and maximum deformation;
  
• The results of the FE model parametric study carried out to fit the measured lateral pipeline configuration using the classical “trial and error” optimisation technique;
  
• Description of the optimisation processes used in ModeFrontier and selection of the “Pareto curve”;
  
• Comparison of the output values subsequently the optimisation process with respect to the design targets and considerations about the saving time calculation and the results accuracy achieved.