Vessel motion based criteria for pipeline Abandonment and Recovery operations

Offshore pipeline installation is limited by pipeline integrity during the laying process. Pipeline integrity is evaluated with the help of buckling checks, which help determining the feasibility of pipeline installation for a given sea condition. The operational limit of pipeline installation is determined during project preparation, by outlining a limiting sea condition (A standard, undirectional wave spectra) beyond which pipeline damage is assumed to occur. Therefore, the installation process is interrupted during such a sea condition and the pipe is abandoned. The pipe is recovered when the weather improves, for further installation. This entire process is termed as Abandonment and Recovery (A&R) operation. In reality, the offshore sea conditions encountered during operation are different in nature, when compared to the sea-state outlined during project preparation (non-standard, multidirectional sea spectrum). This creates an uncertainty in the decision making process for pipeline abandonment. In order to overcome this, an A&R criterion is desired, which is insensitive to the sea-state definition. The criterion should be based on vessel motion parameters. The goal of this thesis is to predict the extreme response of pipeline based on vessel motions, in order to evaluate the integrity of pipeline for a given environment. Three statistical models were developed during the course of the study, to predict the extreme responses of pipeline using one or more input parameters among all the vessel motions; for a given installation case. These models require the generation of a database for each installation case, the output of which results in predictive formulas with a certain degree of confidence. The report consists of two main parts. The first part describes in detail, the procedure employed for a given installation case, right from database generation to data gathering and postprocessing analysis, resulting in three statistical models that predicts the extreme response in the sagbend part of the suspended pipeline. This procedure/method has been generalised for any type of installation case (small and large water depths, flexible and stiff pipelines). The second part of the report shows the results of the procedure, for two sample installation cases; one in deep water and the other in shallow water. The models are validated for different kinds of randomly chosen sea-spectra, that are assumed to be representative of the offshore environment. This is then followed by the analysis of results and discussions about various aspects of the procedure, adopted in this research.

Subject

Offshore pipelines
vessel motions
S-lay method
pipeline integrity
sagbend
statistical modeling
multiple regression
deep water pipelay
shallow water pipelay
Orcaflex
OFFPIPE

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http://resolver.tudelft.nl/uuid:5374e1ef-0375-4bff-8d3a-068d6aed9c9e

Embargo date

2021-10-01

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Student theses

Document type

master thesis

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Thesis - R.K.Sri Paravastu.pdf

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