Risk-Based Structural Integrity Management (SIM) Strategies represent an important development in the safe and efficient management of FPSO hull structural integrity. In recent times, Marine Technical Limits (MTL) have developed several risk-based SIM strategies for a range of floating facilities. DNV has recently approved the first of these strategies for use.
A SIM strategy should define the frequency and scope of inspection activities and provide a framework for continuous evaluation of the hull structure. The traditional approach is to follow a prescriptive 5-year Class cycle. Inspecting each tank on the vessel within a 5-year period ensures that all spaces are periodically inspected. However, this approach is generic and potentially inefficient.
Risk-based structural integrity management offers an alternative. Using this approach, the inspection scope and strategy is based on the actual risk profile for that vessel. The strategy describes the details of each space and structure on an asset, as well as the risks and mitigations that exist. This enables inspection scopes and frequencies to be set based on the risk profile of each space and structure, while being continually reviewed and updated to ensure it remains valid. When correctly implemented, this delivers a targeted and efficient strategy.
Risk-Based SIM Strategy Development
MTL have created an effective process for the development of risk-based SIM strategies. We have applied this method to both newbuild and existing assets. Each time we have demonstrated a progressive and cost-effective approach to strategy development. This is carried out using MTL’s bespoke RBIM risk software combined with MTL’s structural integrity management software, PYXIS.
The three-stage development process is as follows:
Stage 1: Data collection and review
This step includes a full review of vessel drawings, construction records, tank coating specifications and structural strength and fatigue analysis. In addition, for existing vessels the review will cover inspection reports, outstanding anomaly records and previous repairs.
Stage 2: Risk assessment
Our in-house risk assessment software utilises a similar process to that of a task-based risk assessment. We quantify degradation mechanisms and map them to structural elements thereby providing a clear link between risk and a need to inspect. The assessment incorporates the output from the initial review stage, in addition to any mitigations such as ongoing or planned repairs. As a result each structure or space is assessed to produce a risk ranking for use in the development of the inspection plan.
Stage 3: Development of documentation
The output of the initial review and the risk assessment define the development of the SIM strategy and in service inspection plan. The documentation produced covers the inspection management and anomaly management processes. It also details the principles of the integrity review cycle and the scope and frequency of inspection activities for the asset.
The development of the risk-based SIM strategy is only the first step of applying a risk-based approach. With the strategy and inspection plans set out, it is imperative that these are acted on and are applied through a well-managed implementation of the strategy.
The successful implementation of a risk-based SIM strategy requires a number of inputs. Firstly robust inspection management, underpinned by a regime of positive reporting. Secondly, thorough anomaly management processes should assess, catalogue and store inspection findings. In addition, it is important to continually review and assess the output of ongoing inspections. This information is fed back into the strategy. As a result the risk profile of each structure or space is updated as required following an inspection, incorporating all available inspection and anomaly data.
MTL’s integrity management software, PYXIS, enables a user to fully understand the condition of an asset. PYXIS enables full management of risk-based SIM strategies to:
• define inspections
• manage findings and anomalies
• store inspection information and statistics
• develop predictive degradation models
This delivers continual management of an assets risk-based SIM strategy and enables a full understanding of the hull structure.
Benefits of a Risk-Based approach
The main advantages of a risk-based approach are as follows:
• Asset managers can understand where the key risks are on a vessel and the reasoning behind entering a specific space to undertake inspection tasks. As a result, there is an appreciation of how a specific inspection relates to the overall vessel risk profile. Consequently, asset managers are able to understand and prioritise the management of risk more effectively.
• It enables effective use of resources. This is particularly important in the current climate and where assets have POB limitations.
• A risk-based approach will not necessarily reduce the inspection burden, however the frequency of inspection required for each tank/space will be tailored to the specific needs of the asset.
In summary, a robust risk-based SIM strategy represents an efficient, tailored approach to structural integrity management when compared to more traditional methods. A risk-based approach provides a more comprehensive understanding of an asset’s risk profile. Ultimately it enables appropriate choices to be made based on the risk profile.