A well planned and executed Structural Integrity Management (SIM) program is the cornerstone of managing structural risks and it can greatly reduce unplanned, undesired and extremely costly in-situ structural repairs on floating offshore facilities. However, the level of effort, required resources and ultimately the operating costs to maintain offshore structures can be greatly influenced by decisions and assumptions made during design and construction. This is particularly the case for Floating Production Storage and Offloading (FPSO) units because of the added complexities and consequences related to the oil storage and offloading. Though, there are several examples of other floating facility types (e.g., Semisubmersibles, Spars, etc.) where decisions in design influenced the ease, or conversely the difficulty, maintaining the asset's structural integrity over the operating life.
This paper provides general guidance on design and construction decisions that can help enhance the planning and execution of a SIM program while improving the long term structural integrity performance of offshore floating structures. Examples are also provided where design and construction decisions have been observed to positively or negatively influence the long term integrity of floating offshore structure hulls and marine systems during operation. The observations and examples are drawn directly from the authors' experiences supporting major oil and gas companies operating in Australia, West Africa and the Gulf of Mexico regions to develop, manage and execute offshore fleet SIM programs.
For floating facilities, from the onset of the project development, the primary focus is how to safely and effectively produce the oil or gas reservoir given the multitude of the parameters (e.g., drilling program, water depth, environment, existing infrastructure, etc.). Once the project is sanctioned, the race is on to first oil with project safety, cost and schedule driving the design and construction. These drivers are associated with the project Capital Expenditures (CAPEX). When project costs and schedule are tight, which is most often the case; decisions on ways to manage the project cost and schedule often shift the costs and associated effort onto the facility operations. This inevitably impacts the Operating Expenditures (OPEX). For hulls and marine systems, examples of these types of project decisions may include not coating certain tanks or using cheaper, less corrosion resistant piping. These decisions reduce project costs, but the long term maintainability and operability costs will be higher. This puts additional burden on operations. Safety is not compromised, provided operations can maintain these structures and systems. Hence, a robust SIM program and adequate resources to support and execute the program are essential. Issues arise when operations cannot keep up with the maintenance of the structures / systems. Additionally, the costs associated with maintaining and repairing the structures and systems offshore can become quite burdensome, especially later in life when waning production requires reduced OPEX levels to maintain economic viability. The tradeoffs between project CAPEX decisions and long term OPEX maintenance and repair costs are common themes in the later sections of this paper.
Another important aspect during the initial project development phases is ensuring the design and construction philosophy is aligned with the planned operations and SIM program. This philosophy represents the initial foundation for the SIM program. Design safety margins, corrosion protection strategy and construction quality programs will influence the SIM program requirements and execution over the floating asset's life. Input from operations is imperative to help validate the strategies and assumptions regarding how the structure and systems will be operated and maintained.