Structural integrity management and improved joint flexibility equations for uni-planar k-type tubular joints of fixed offshore structures

摘要

The distribution of fixed steel offshore platforms around the world reveal a global fleet thatudhas exceeded or is approaching the end of the design life. In many operating areas, there is anudattraction to continue using these aging facilities due to continued production or as anudadjoining structure to facilitate a new field development or expansion. To justify continuedudlife extension of the fixed platform, various integrity assessment techniques are often used.udOne of the major techniques incorporated is the phenomena of Local Joint Flexibility (LJF).udThe derivations of existing LJF equations have evolved in many ways, including use of finiteudelement methods to predict the joint behaviour. There has been insufficient credibleudbenchmarking to large scale experimental test data.udIn the early 1980s, AMOCO performed the only large scale test results of LJF which, priorudto this research, has not been in the public domain. A major objective of this research is touddevelop a suite of improved LJF equations that have been appropriately benchmarked to largeudscale tests. In addition, with the issue of the API RP 2SIM (2014) 1st Edition and theuddevelopment of the ISO 19901-09 SIM (DIS), this research also provides a basis for furtherudAsset Life Extension (ALE) of an aging fixed offshore platform in terms of ultimate strengthudby using an improved suite of LJF equations. Furthermore, the research puts the structuraludassessments such as LJF in the context of a structural integrity management framework,udwhich enables operators to manage their facilities holistically rather than isolated processes.udThe research within this thesis critically examined the suitability of the existing LJFudequations, reviewed the guidance provided in the existing studies and described theirudlimitations for gapped K-type tubular joints. A comparison study and benchmarking studyuddemonstrated that a proposed finite element model provides a good fit with large scaleudexperimental data (AMOCO) and was used to develop a suite of improved LJF equations for gapped K-type tubular joints. The LJF equations derived from this research were validatedudagainst the BOMEL large scale structural frame tests in terms of ultimate strength anduddemonstrated an improvement on the current MSL-1SO equations for uni-planar K-typeudtubular joints in the ISO 19902.2007 Fixed Offshore Structures code of practice. Thisudresearch also provides a basis to update current offshore structures codes and standards foruduni-planar gapped K-joints and also provide a standardized methodology for the derivation ofudLJFs from credible large scale test data for other tubular joint configurations including multiplanarudK-joints, T-joints, Y-joints and X-joints.udThe LJF equations developed in this research will have high impact in terms of the structuraludintegrity management of fixed offshore structures for OGPs globally, as they provide anudimprovement to the current MSL-ISO joint equations, for gapped uni-planar joints. Offshoreudstructures are now able to operate more safely without compromising structural integrity andudincurring costly underwater repairs and inspections as before. OGPs are now able to prioritizeudlimited resources to other areas of concerns based on ALARP principles.