RELIABILITY ASSESSMENT APPROACH FOR DCV AEGIR PIPELINE INSTALLATION ANALYSES

摘要

Heerema Marine Contractors (HMC) is entering a new era of pipe laying with the new Deepwater Construction Vessel (DCV) Aegir. This vessel is designed to be able to reel/J-lay pipelines for a wide range of pipe dimension and water depth combinations. To define the limit of installation workability windows, the pipeline installation analyses (reeling or J-lay method) during the project engineering preparation phase are normally performed based on the consideration that a combination of several "worst case" scenarios will occur at the same time during the installation event. The worst case scenarios are assumed in terms of pipe resistance (geometry/property), positioning of the vessel/equipment, environmental loads, etc. This method of calculations can be considered as the most practical and safe approach. However, as an accumulation of conservative assumptions is inherently being made within this approach, it can lead to a situation that the pipeline cannot be installed or lead to insufficient workability window for pipeline installation operation. Another shortcoming of this worst case scenario approach is that we are not able to quantify the probability of failure for a certain pipeline installation scenario. The reliability analyses and assessment for pipeline construction/installation as described in the DNV-OS-F101 code can be used as an alternative. The assessment can lead to some relaxations of the pipeline installation workability in a safe manner whilst accepting some level of the risks. The purpose of this paper is to present the development of reliability assessment approach for pipeline installation analyses for the DCV Aegir. One of the important steps of the development is the setup of a pipeline database based on the as-built pipeline data from HMC's past projects. The database can be used to estimate the typical distributions of the pipe dimension and properties as input for the reliability analyses. Three examples are given in this paper, two are related to the reeling pipeline analysis with standard pipe ends and counterbored pipe ends (First Order Reliability Method FORM and Monte Carlo approach) and another example is related to J-lay pipeline installation analysis. The results of the assessments are correlated with the DNV guideline for the acceptance of nominal target probability of failures against the safety classes.