Regardless of its sturdiness, the lifetime of an offshore platform is not at all eternal when exposed to extreme weather conditions, dynamic forces and accumulated fatigue damage. However, with remaining oil reserves still to be produced, operators are highly interested in keeping ageing structures on-stream for as long as possible through lifetime extension initiatives. The options for lifetime extension are many and various, but investments can reach high proportions. The whole process can become one costly affair if we are to add the frequency of inspection planning (RBI), man hours, and material used in rationalisation or structural reinforcement operations.
Structural Health Monitoring (SHM) is a technique which has the potential to significantly reduce costs related to keeping old platforms on-stream for a period beyond the original design life. Combining a variety of sensing technologies with an embedded measurement controller to log and analyse real-time data, SHM systems (SHMS) add an entirely innovative vantage to the lifetime extension discipline. Information about the occurring conditions/changes of a platform is obtained through installation of a communication unit along with strain gauges, accelerometers, wave radars and GPS mounted on the platform.
As the installation process is highly flexible, SHMS are an option for various types of structures. For instance, at the engineering consultancy Ramboll Oil & Gas, engineers have worked with the entire SHMS lifecycle for more than 15 years not only for offshore platforms, but also for buildings, wind turbines, and bridges.
The greatest asset of SHMS is that it can be revised and revamped so that the inherent possibilities of using it become richer and more diverse. Ramboll’s expertise has been strengthened over the last decade and the SHMS services have been constantly improved as the company managed to develop its own intelligent analysis system.
A way of converting the existing SHMS data and feeding it into the existing finite element model of the platform makes it possible by advanced analysis methods to measure and assess the actual condition of the structure.
Another innovative asset is the development of online damage detection tools which are able to detect structural changes in real-time, warning the operator when SHMS indicators exceed pre-defined values.
Additionally, troubleshooting is performed when insufficiently understood responses are detected on structures. The detected changes are treated from their root cause through time-limited or automated measurement campaigns that are able to identify the sources that produced them initially.
Essentially, the mechanism of SHMS is ground-breaking and thanks to its maximum precision, the system enables operators to better plan lifetime extension initiatives via accurate data integration. Valuable information becomes available for the operator during the decision making process with the purpose of reducing costs and increase safety while the risk of failure and disaster is maintained at a very low rate. Instead of inspecting the whole structure of a platform, which is seldom possible, SHMS gives a cost-effective opportunity to decide how often to inspect, and most importantly, where to inspect. Ideally, in some of the cases, the data can show that the structure is doing better than anticipated, facilitating platforms to continue production without any structural changes or reinforcements.
Furthermore, the knowledge gained from SHMS can be incorporated into different design tools to obtain valuable knowledge about the implementation relevant for the design of new platforms. Therefore, besides being cost-effective in terms of lifetime extension initiatives, inspection plans and maintenance activities, SHMS are also resourceful in offering new perspectives on how to tackle the future of the oil and gas industry.
Ulf Tyge Tygesen
Development Manager Global Service Areas, Jackets
Ramboll Oil & Gas
From Adjacent Oil & Gas 3, May 2016