Sammendrag
In recent years there has been a development in the offshore industry to reach deeper waters in an economical and practical way. The floating, production, storage, and offloading unit (FPSO) is one concept that can lower the minimum economic field size and make it possible for the development of remote oil fields in deeper waters. The main objective of this thesis consists of three parts: the first is to understand the aging mechanisms such as fatigue, and corrosion, deformations, and dents. The second is to understand the life extension approaches such as the assessment of offshore structures which are operating beyond their design life, in addition to inspecting methods for evaluating the structural integrity of offshore structures. The third is to investigate the Balder future life extension project at the Rosenberg Worley AS company. This investigation addresses the extent to which the company has performed life extension assessment of the Jotun A FPSO in accordance with relevant regulations, and standards.
The methods used for answering the objective of the thesis is to collect the data through GVI, CVI, and NDT inspections on the ballast tanks and reviewing previous inspection reports. The inspections will also be used to identify corrosion, cracks, and deformations. There will also be performed necessary thickness measurements at the planned locations for further use of actual corrosion deductions in strength assessment. Furthermore, there will be recommended solutions for the deformations and corrosion degradations, supported by calculations and guidelines for replacing deformed parts.
The result of the inspection shows eight material degradation. The inspection reports revealed that most of the findings had minimal to moderate corrosion intensity which is classified as general corrosion. The recommended solutions were to use Hard coating for the findings with corrosion intensity in between 20 % to 50 % and for the ones with corrosion intensity larger than 50 % was to repair by performing grinding, followed by hard coating and in-service inspection.
For the fatigue crack findings, a hot spot fatigue analysis was undertaken on the brackets which were connected to a transverse bulkhead and transverse frame. This analysis was carried out because there were found crack initiations on the frames during the yard inspections. The results showed that the structures had insufficient fatigue strength to carry the loads imposed upon it. Therefore, it has been recommended to renew the damaged brackets so that they may withstand the future operations of the Jotun A FPSO.
The evaluation on the life extension practices addresses the extent of which the company have performed life extension assessment of the Jotun A FPSO in accordance with Norwegian laws, regulations, and standards. The result shows that the company Rosenberg Worley AS are following the standards and regulations.