A number of offshore jacket structures worldwide have already exceeded their designed lifetime. As a result, there is a growing interest to extend the life of the jackets by Structural Health Monitoring (SHM) to ensure the structural integrity, safe operation, failure prevention and control of further degradation. Even though implementing SHM to old jackets incurs additional costs for procurement and installation, the result in the long term will optimize operation and maintenance costs. This can be the main reason that there has been great attention, both within academic research and industrial environment, to the field of SHM in the last few decades. The current research focuses on improving robustness and accuracy of sensors for data collection, processing and evaluation. The objective of the study reported in this article is to explore how developments within SHM tools and approaches can be used to assess structural integrity of old offshore jackets and monitor their performance in a cost-effective manner. A monitoring scheme has been proposed by combining local and global measuring techniques. To illustrate the applicability of the proposed monitoring approach, case studies were conducted on a typical offshore jacket. Though there are many different technologies with different characteristics, the proposed technique is found promising for providing effective monitoring results.
Steel jacket-type bottom-fixed structures that are widely used in offshore drilling and supporting offshore operations represent the major part of offshore structures constructed in recent past decades (Wisch, 1998). The dynamic offshore environment exposes these structures to variable cyclic wave loading and the corrosive sea water environment allows minor structural degradation to develop quickly to catastrophic level. To ensure proper and safe operation of the structures, it is very important to have proper maintenance actions with closer monitoring mechanisms. The offshore industry has also invested on ways of understanding the potential implications of unfavorable damage on the structure and its consequences on the offshore industrial facilities and human life. In particular, closer monitoring of the structures is more crucial when they are operated during their extended life, i.e. operation beyond the designed service life. As a measure to ensure structural integrity of these offshore structures, improve safe operation and extended service life, diverse forms of SHM actions have been implemented (Stacey, et al. 2008; Rouhan and Schoefs, 2003, Ersdal and Hörnlund, 2008). Monitoring degradation symptoms of aging offshore structures is particularly important because of the potential consequences that a minor damage may have on such structures and hence periodic inspection of damage indication is mandatory. In addition, several factors such as the unfavorable and harsh offshore environment makes periodic inspections necessary.