Full-Scale Testing of Flexible Riser System Subjected to Internal Flow-Induced Vibration
Notice bibliographique
Résumé
Abstract Noise and vibration in flexible riser production systems exporting dry gas can cause failure of small bore connections due to fatigue-induced vibration. The fundamental cause is vortex shedding within the corrugated, flexible riser. Small scale testing and Finite Element modeling have been used to demonstrate the extent of the problem and the conditions under which it might occur. These model results agreed with measurements which were made on the Schiehallion FPSO operating West of Shetland. A means has been developed and proved experimentally to test full scale equipment at operational dynamic and static pressures with a gas flow of natural gas. This methodology was used to test a replica of the Flow Termination Assembly currently deployed sub-sea on Schiehallion. The work showed that a fatigue failure was indeed possible, but the necessarily unfavourable condition had not occurred to date. We were able to show under what conditions it might occur and to explain why it had not occurred to date. Finally a means to mitigate the potential problem was developed, proved and deployed. The work allowed the continued operation of the export line without risk of fatigue failure and for the production flow rate to be safely, further increased. Introduction Flexible risers are increasingly being used offshore and most recently for the export of dry gas. This has led to the phenomenon of the singing riser whereby large pressure fluctuations within the riser can be heard as acoustic tones. If the frequency of the tones is coincident with the structural natural frequency of the equipment associated with the riser, large amplitude vibrations may be excited. This might lead to fatigue failure. This phenomenon is widespread on many systems. It affected the export riser system of the BP Schiehallion FPSO. Modifications were made to the affected topside equipment to avoid fatigue damage. However, it was not known if there was likely to be a problem with the sub-sea 'Flow Termination Assembly', FTA. Some limited sub-sea measurements did indicate high vibration levels although there was not sufficient instrumentation to determine the associated stresses. As a consequence of these measurements flow restrictions were imposed to maintain the topsides and sub-sea vibration within limits. The operator sought assurance that the sub-sea system could safely be operated up to design capacity significantly in excess of the operational limit. A consortium was formed by the authors to investigate the problem. Our work involved Finite Element modeling and small scale, atmospheric, acoustic testing which demonstrated the likelihood of high stress levels and the condition under which they would occur. However, the scaling laws were not understood and it was not possible to model several of the parameters, either numerically or at small scale. Full scale testing was therefore done and a description of this work forms the major part of this paper. A replica of the FTA deployed on Schiehallion was tested in a flow loop using methane at the full scale export pressure of 170 bar. The dynamic pressure fluctuations, mimicking those within the riser, were provided by a siren.
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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,001 | 0,001 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».