Through-life integrity management of deepwater subsea systems

Chris Saunders - MCS

Deepwater subsea systems operate in relatively inaccessible locations. This makes them difficult to inspect, repair, and maintain. As a result, operators increasingly see the benefits of integrity management systems to optimize inspection and repair strategies to increase system availability, and to reduce opex costs. To achieve this, some investment must be made up front.

The main problem associated with delivering a quality integrity management strategy is not technical understanding, but a commitment to implementation. An integrity management system cannot be considered as a collection of procedural and instructional documents. It is a “live” tool that enables integrity data to be analyzed, understood, and the status of the system determined.

Long-term plans

Integrity management of subsea systems has been adopted historically by the industry where there has been a local legislative or corporate requirement to do so. A recent example is in the US Gulf of Mexico, where draft regulations published in October 2007 require for the first time risk-based integrity management of riser systems.

More specifically, the regulations call for a documented Integrity Management program, an emergency response plan, and a personnel qualification program. These various measures would put US Gulf operations on par with the regime that came into force in the UK post-Piper Alpha.

Traditionally, the drivers for integrity management have been to ensure a safe system is in operation and to increase system availability in the short term. Today, however, operators look increasingly at their integrity management systems as a means to extend field life past the original design conditions. The quantity and quality of data required to make these assessments can be significant.

Integrity management of deepwater subsea systems is a special case, given the cost of subsea inspection and intervention, the limited inspection intervals available, the lead times for replacement or repair, and the emergence of new technologies for deeper and harsher environments. New inspection and measurement tools are being developed to mitigate some of these challenges, and more operators are considering implementing integrity management at the front-end engineering and design stages of new installations.

In recent years, operators have identified additional, non-regulatory benefits of an integrity management strategy, which include:

• Long-term field planning for life extension or re-use
• Reduced inspection costs through rationalization
• Next generation design benefits through capturing lessons learned
• An ability to plan proactively for repair and maintenance, rather than reacting to problems as they occur
• Increased system uptime and availability
• Spares rationalization.

Integrity management systems have three main building blocks:

1. Risk assessment
2. Inspection/monitoring strategy
3. Periodic review.

Depending on the subsea component, guidance exists in the form of API / ISO specification, regulator guidance notes, or joint industry projects detailing how to technically conduct the assessments. One of the main problems associated with subsea integrity management systems is the vast quantity and range of data required. This can include:

• Historical process and production data such as pressure, temperature, flow rate, pH, composition
• Erosion and corrosion probe data
• Chemical injection data and material sample test results
• Dropped object register
• Vessel motion and metocean data
• Manufacturing history
• Design documentation
• Corporate and regulatory governance
• Risk assessment methods and results
• Corrosion management strategies
• Detailed inspection procedures and offshore work packs
• GVI and CVI videos and images
• Industry advances and best practices
• Future field requirements
• Specialist analysis and reports
• Pigging results.

All this data typically resides in separate and individual databases. In certain cases, cross-referencing data becomes difficult and is often considered in isolation. Data quality also can become an issue on aging installations where, over time, subsea sensors and topside probes have stopped functioning or limited data is available due to a lack of remaining system redundancy. Key staff change-out over the life of the asset adds another dimension. Other problems with data management include legacy systems, information exchange, and handover during ownership change.

Unless new technology for integrity management is considered during the early design stages of a subsea development, it can become technically or commercially prohibitive to retrofit. With different staff managing the opex and capex budgets, it can be difficult to make an argument for upfront investment, even where this is a relatively small value. This is true especially at the early stages of asset design when the opex budgets may not have been identified.

Commonly, integrity management systems focus on present-day status based on historical conditions. Very little time, however, is devoted to considering the system’s future suitability. Equally, subsea systems tend to be considered on a component-by-component basis which can mean that the bigger picture of the system integrity is missed.

Improving data quality

There are various methods and processes that an operator can adopt to improve the quality of inspection data gathered by ROVs. One way is to provide the ROV operator with a detailed set of inspection requirement documents prepared in advance of the survey. Alternatively, an integrity specialist can act as a client representative offshore during the inspection campaign so that decisions can be made on-site, limiting the need for follow-up surveys.

Software solutions are available that can analyze online process data quality, and use the data to undertake an integrity assessment for the system. The integrity status of the system is updated on a “continual/live” basis, preventing continued damage that may not have been detected until the next periodic review.