Deepwater pipeline inline inspection – a tool box approach

Summary

To ensure continuity of hydrocarbon supply, opportunities are sought by Exploration & Production companies in continually increasing water depths. A range of pipeline technologies and manufacture methods are generally employed to increase the technical feasibility of Deepwater developments. While a combination of pipeline types facilitates high pressure and high flow production, it also brings challenges for internal inspection techniques due to an amalgamation of demanding inspection criteria such as: heavy wall thickness, high temperature and pressure, flexible riser transit, trap constraints and internal diameter reductions.

To address these challenges, ROSEN is able to provide a holistic approach to inspection, whereby a portfolio of solutions can be considered, offering maximum flexibility to pipeline designers, with an aim to deliver optimum integrity data while also mitigating risk. This paper will discuss ROSENs toolbox approach to Deepwater pipeline inspection through presentation of case studies.

Introduction to the approach

Subsea pipeline systems pose numerous unique challenges for In Line Inspection (ILI), distinct from those encountered with onshore pipelines. These challenges stem from both the difficult access to underwater facilities and their connection to structures above the water's surface.

Figure 1: Example of a Deepwater Field Layout

Starting with the launching process, the inherent complexities become apparent, as the usual flow direction is from wells and production lines through manifolds and flow lines to the platform or FPSO. In most cases, pigging of the production lines is not feasible because neither the wellheads nor the manifolds are designed for such operations. For the flow lines, launchers are situated on a platform, vessel, or sometimes temporarily subsea. Given the intricacy of subsea launching operations, looped systems are often employed. Looped layouts consist of two parallel lines of the same diameter running between the manifold and the topside facility, with the possibility of a connected loop at the manifold. This arrangement allows both lines to be inspected in a single inspection run with the launcher and receiver at the same location, minimizing subsea activities (except for valve operations). When this option is unavailable along with restricted subsea launch and receive facilities, flow lines can be inspected using bidirectional tools, self-propelled umbilical tools or tethered tools.

The transportation of the medium presents its own set of challenges. Typically, a platform gathers flow from multiple flow lines, leading to an increase in overall volume for export, necessitating larger pipeline diameters. However, larger installations are costly, and riser pipelines are limited in maximum diameter. Consequently, dual or multi-diameter pipeline systems are often used. Additionally, platforms and production vessels experience movement due to waves, wind, currents, and tides, requiring flexibility in the respective pipeline segment (riser). To address this, various solutions are available, such as flexible risers, steel catenary risers, and lazy wave rigid risers. All of these can pose additional challenges for inline inspection (ILI).

Export pipelines typically run straight for long distances until they reach an onshore facility or the next platform. However, these systems often expand due to the declining production of old wells and the addition of production from new wells and platforms. This expansion usually involves the use of tie-ins, often realized with wye pieces. Moreover, the flow from the original pipeline may be very low and only increase after the new tie-ins, which can also present challenges for ILI tool velocity. Inspecting these systems through the new tie-ins often involves different pipeline diameters and navigating the passage of a wye typically with side flow.

Typically, subsea installations (wyes, manifolds, jumpers, tie-in spools) are compatible for pigging, particularly when considered in isolation, however these geometrical complexities may assume critical significance, particularly when situated in proximity to other installations like subsea connectors, valves, and tees. All of these challenges are compounded by operational conditions characterized by high flow velocities and high pressure. Considering the potentially severe consequences of issues during an ILI inspection of a subsea pipeline, it becomes evident how crucial and complex the preparation for such projects is, and why testing is sometimes key.

In response to the challenges raised by Deepwater environments, ROSEN is able to deliver flexible and customized inspection solutions, whereby tools are developed, manufactured and tested in-house. To identify the optimal solution the “ROSEN Toolbox” approach is employed. ROSEN is able to provide a holistic approach to inspection, whereby a portfolio of solutions can be considered, offering maximum flexibility to pipeline designers, with an aim to deliver optimum integrity data while also mitigating risk.

This technical paper examines the multifaceted challenges associated with Deepwater pipelines in the context of pigging and will discuss three case studies, highlighting the individual challenges and successful ROSEN solutions:

• Case Study 1: Safe passage of Magnetic Flux Leakage (MFL-A) tools in flexible pipes
• Case Study 2: A Deepwater Multi-diameter Gas Pipeline
• Service Overview: Deepwater high pressure riser inspection with self-propelled tethered tools

For the complete paper and/or further information contact Lauren Guest, ROSEN Europe.