Clarus Subsea Integrity Inc.
A risk assessment is a tool commonly employed by operators during the stages of an asset's life cycle, and can be used to varying degrees of depth and detail. Whether it is qualitative, quantitative, safety case, or anomaly-based, most operators use risk assessment techniques to identify critical components and prioritize inspection, maintenance, and repair work.
To maximize the value of risk assessments, there are a number of practical improvements that can help overcome challenges frequently faced during the application of risk assessment techniques. These allow the risk assessment process to be a multi-purpose tool to improve the overall performance of the integrity program.
Qualitative risk assessments can be highly influenced by the human factor, depending on the participants and experiences involved in the process. An organization-wide common risk assessment procedure allows integrity features to be consistently evaluated and reported. As a result, integrity, and performance of assets can be compared globally across the organization, and resource utilization can be optimized. Another advantage is increased knowledge sharing and risk management solutions across regions for similar degradation mechanisms.
A key element in implementing common risk assessment approach is having predefined risk events corresponding to different degradation mechanisms. For example, consider external corrosion on splash zone hull piping, a commonly observed feature offshore. One example of a risk event might be excessively reduced wall thickness, resulting in de-rating of the line for continued operation. Another example might be that excessive corrosion leads to hydrocarbon leakage with a potential for ignition due to proximity to hot work area, resulting in shutdown.
Both of these two risk events are credible, yet lead to different risk evaluation. While de-rating of line results in reduced production, a hydrocarbon leak with potential for ignition is a predominantly health and safety risk, and even results in higher production impact than the former case.
|Depiction of the impact of subsea equipment functionality on a risk level. (All images courtesy Clarus Subsea Integrity Inc.)|
An educational process
When assessing the risk of failure from degradation mechanisms to a particular component, it is crucial to gather all relevant data on the component for an accurate assessment. Data comes from design, fabrication, installation, and operations phases of the component, such as outer diameter, wall thickness, corrosion allowance, coating properties, design life, historic inspection, and condition monitoring data.
The data-gathering process creates a powerful database of the essential attributes associated with different equipment for different assets. A significant benefit of this exercise is visibility in data gaps that can be actively managed for closure and can become key assumptions while assessing risks.
Structured risk assessment processes also help to identify the data required to verify effectiveness of design barriers and measure levels of degradations and technology. While several proven inspection and monitoring techniques are available in the industry to gather this data, gaps in technology and challenges in application of technology to particular assets can be identified through this process. This information becomes valuable feedback for future designs and in development of new technology to address existing data gathering challenges.
A well-documented and maintained risk assessment serves as a comprehensive system overview and asset performance record through asset lifecycle and personnel changes.
In addition to component data, it is imperative to document the assumptions during the process. Not only are the assumptions crucial to the risk determination during the assessment, they also allow for efficient review, update, and re-validation of the assessment outcome at a future date.
Some typical assumptions include system redundancy, availability of spares, and the time required to mobilize a vessel inspection or equipment replacements. Availability of inspection data also influences the assumptions made during a risk assessment and should be taken into account when determining the likelihood of risk events. For example, availability of in-line inspection (ILI) data and assessed defects on a flowline increases the confidence in assessing risk of leak from internal corrosion of a flowline. However, in the absence of ILI, it is prudent to assume a slightly higher likelihood for a risk of leak from internal corrosion due to the lack of direct measurement of wall thickness.
Consider a production loop with two wells, where Well 1 production flows through Flowline 1 and Well 2 production flows through Flowline 2. The two wells are tied back to the same manifold with an isolation valve directing the flow to the appropriate flowlines.
For a risk event of blockage somewhere along Flowline 1 consider the following scenario: The isolation valve is not in a state to function due to inactivity since field start-up. Well 1 has to shut in until the blockage in Flowline 1 is remediated. This activity may take months to resolve and will require a rush response. The production downtime consequence of this blockage is high.
Now, consider a second scenario: The isolation valve is routinely maintained and tested and found to be in good condition. The operation team is able to redirect production from Well 1 through Flowline 2. Well 1 does not have to shut in and is able to produce at reduced capacity, while blockage remediation is in progress. The ability to utilize this redundancy in the system significantly reduces the production downtime associated with this blockage as compared to the previous scenario.
Quantitative risk assessments
Qualitative risk assessments have a huge human influence and hence, there is a tendency to require quantitative data to reduce the human bias. Industry failure databases are available that allow operators to report failures anonymously. While these databases are great tools, some challenges with its use include lack of data on certain equipment, inconsistent failure categorization by users, and, often, incomplete data entries. This result in skewed statistics and direct application of this data in assessing likelihoods of failure may lead to inaccurate assessments.
The deepwater offshore oil and gas industry is still young and with that comes lack of sufficient data for reliable predictions. Technology advancement has led to changes in subsea equipment design with multiple equipment generations over past couple decades. Hence, even with available failure data, its relevance for reliability is a limitation due to evolving technology used in different assets globally.
Since there is a lack of statistically significant failure data, individual operators may want to supplement the reliability data with integrity management anomalies observed during operations. Anomalies are signs of degradation or deviation from design that, if unattended, may lead to a failure. When tracked and trended, anomalies can be a more direct reflection of the equipment performance over time, and thus can be used to influence the determination of risk likelihoods.
|Representation of an asset life cycle with varying risks.|
Until sufficient relevant data is available, purely quantitative risk assessments are not feasible. The best approach is to perform qualitative risk assessment with reliability data for reference and have assessments validated by subject matter experts.
A commonly faced challenge is lack of representation from key stakeholders during risk assessment reviews. This results in differing perceptions of risk levels from the risk assessors as compared to those implementing the integrity recommendations. With overwhelming and frequently competing priorities during operation, the necessity of proactive risk management activities such as inspection and monitoring may be questioned.
For example, studies have shown that when marine growth on riser strakes exceed approximately a third of its fin height, its ability to mitigate vortex induced vibrations is reduced and fatigue damage unaccounted for during design may occur in the risers. It is therefore necessary to periodically clean the strakes to maintain their efficiency. If the reason to do so is not well understood, the inspection execution team may question the need for ROV and vessel time to clean the strakes at such a frequency.
It is invaluable to have the right stake holders validate and understand the risk assessment process, assumptions, risk levels, and resulting integrity recommendations.
The risk assessment process not only defines risk management activities, but also identifies gaps that need to be addressed within design and spare philosophy. Understanding data required for active management of degradation mechanisms from existing assets benefits future design improvements and advanced inspection and monitoring techniques to gather relevant integrity data.
The results of the risk assessment can also help to determine the need for spare parts. Supply chain management failures, for example, a common occurrence, are internal to the pod and would require replacement of the pod to restore functionality of the equipment. Even though there is an initial investment, by having one readily installable spare, the production downtime can be considerably reduced.
Knowledge loss over asset life cycle is a credible and real challenge. Documentation of all the required information and assumptions required to perform risk assessment helps to alleviate the information loss observed during handover of an asset from design to operations. However, maintaining visibility of varying risk levels and types through operation stage of an asset is a unique challenge. Periodic risk reviews is the avenue to capture changes in risk levels and operational conditions thereby offering an opportunity to adjust risk management strategies. A significant benefit from this approach is realized when evaluating feasibility of life extension and during decommissioning.
Over time changes due to aging, wear, and operating conditions lead to changes in the risk levels. The production fluid composition may be altered by changes in reservoir characteristics with time. Coating degradation in the splash zone may lead to corrosion under coating, resulting in wall loss. Similar examples of observed features if unaccounted for reduce the effectiveness of integrity management programs. Risk assessment is a platform for detailed review of degradation mechanisms and corresponding risk mitigation strategies. As with any plans or regulations, risk assessment should hence be reviewed and audited periodically to ensure that it accurately reflects the system's current conditions.
With the above described improvements, a risk assessment can be a powerful tool to improve the efficiency and effectiveness of integrity management programs globally within an organization. By ensuring a consistent approach and documenting the assumptions and current equipment conditions, risk assessments can be used to educate personnel, maintain system data and operating condition, offer knowledge sharing, and promote more proactive management of operational risks. Finally, through periodic reviews risk management strategies can be continually maintained for relevance and effectiveness for asset integrity management. •