An investigation of the response of an FPSOV structures to external air blast :a case study of FPSOV operating in the Niger Delta

Abstract

Floating production storage and offloading systems, otherwise known as FPSOs in the oil and gas industry, are high risk structures because of their exposure to hazardous and flammable hydrocarbons which they carry and in some situations, because of their vulnerability to terrorist attack especially in their areas of operation. These structures have been widely used for the development of offshore oil and gas fields all over the world, especially in most part of Africa, because of their attractive features such as large work area and storage capacity, relative lower cost of construction and good stability. They are either converted from existing tankers or bulk carriers or purposely built. However the recent wave of terrorism across the Nigerian Niger Delta has necessitated the study for the need for offshore structures especially FPSO to be protected from the activities of terrorist. One of the worst case scenarios that is likely to occur on an FPSO is an attack by terrorist resulting in an above water external air blast on the side plate of a midship section of an FPSO. The resulting damage effects that would be caused by this form of attack can be devastating in terms of loss of revenue to a nation, loss of life, assets and degradation to the local environment. This was tragically demonstrated in the North Sea with the loss of the Piper Alpha Platform mentioned by (lees, 1996), albeit initiated by an accidental internal blast, unrelated to terrorist activities. At present, most design methods on the midshipsection structural members of a merchant vessel are based on working stress design concepts that are safe and suitable for normal pre-commissioning and operating conditions and which emphasize the minimum acceptable requirement for the classification society. However, design under extreme air blast loading especially those typical of terrorist/Militant attack, whose magnitude would be far higher than ordinary operating load, are desirable. In order to make it a major design consideration, this study addressed this issue on minimizing the effects of blast overpressure through the evaluation of the 3 types of T stiffeners and 3 L stiffeners to local structural response of such blast pressure on the side shell of the midshipsection of a typical FPSO code named FPSO Nigeria. The Nigerian Niger Delta accounts for over 95% of Nigerian oil and foreign reserve earning, and has been a source of attack and insurgence by militant of the Niger Delta. The objective of this study is to examine an above water air blast pressure attack to the side plate of a midshipsection of an FPSO code named FPSO Nigeria. This blast pressure is converted to an equivalent amount of TNT explosive typical to that which may be used by the militants of the Nigeria Niger delta or other parts of the world and to v KAZEEM SHITTU-An Investigation Of The Response OF AN FPSOVStructure To External Blast: A Case Study Of FPSOV Operating In The Niger Delta recommend ways by which an FPSO operating in this area could be made more resilient to terrorist attack to a larger extent or at least to minimize terrorist caused damage to the barest minimum by the selection of the best of the 3 types of T and L stiffeners considered. Additionally, blast resistant anti-ballistic material was recommended and a cost benefit analysis carried out in order to justify the need and the importance of using such blast resistance anti-ballistic materials. In order to achieve the aim of the thesis, the study commenced with the investigation of the displacement and stresses of plates and stiffened plates using Abaqus software code and compared the results of displacement and stresses generated from Abaqus with that of classical theory in order to validate the accuracy of the Software code by considering different plate thickness and boundary conditions, frequency extraction analysis were generated for plates and stiffened plates in order to obtain frequencies at which resonance could occur and to prevent such. The results generated from Abaqus software code were found to correlates with those generated from classical theory. Actual FPSO Nigeria stiffened panel were then considered and subjected to non-linear blast analysis under different boundary conditions where effects of mesh refinement were considered in details. The mid ship section of the above water side of the FPSO Nigeria was then subjected to blast pressure attack considering the different type of stiffeners with a view to determine the best stiffener configuration and to determine the rupture strain consequently an anti-ballistic blast resistant material was recommended as an aftermath of Cost Benefit analysis was carried out to validate the need for such anti-ballistic blast resistance material on the above water side of FPSOs operating in the Nigeria Niger Delta and the cost savings to nigerian Government was highlighted vis a vis the loss that would have been incurred by the Government should such attack occurs. The research concentrates mainly on developing an appropriate methodology and an illustrating the behavior of typical ship structures to high rate transient air blast loading effects, rather than undertaking a specific detail design study as such. Consequently the research has made modest contribution to knowledge by the determination of all of the above including the cost benefit analysis carried out.