Unbonded flexible pipes have been widely used in offshore oil and gas developments as an alternative to traditional steel pipes due to their technical advantages and financial benefits particularly...
Unbonded flexible pipes have been widely used in offshore oil and gas developments as an alternative to traditional steel pipes due to their technical advantages and financial benefits particularly for high pressure and high temperature (HPHT) conditions and deep-water applications. In-line inspection (ILI) has been widely adopted as a key source of data for the integrity management of traditional steel pipelines. However, to date limited progress has been made in developing an efficient in-line inspection method suitable for unbonded flexible pipes due to the complexity of their structural characteristics, i.e. multiple layers of different materials and constructions.
The development of ILI technologies that can inspect all layers of unbonded flexible pipes would provide the industry with a step towards change in the integrity management of this asset type. With its specialist experience in design, analysis, manufacturing and operations of offshore unbonded flexible pipes around the world, combined with very strong technical capabilities in pipeline in-line inspection, ROSEN is now developing in-line inspection solutions and associated condition assessment methods to enhance the integrity management of flexible pipes. As a first stage in this development, we have been exploring what value, in terms of integrity management, can be extracted from data collected as ILI tools pass through flexibles.
This paper presents the initial findings from expert review of ILI data collected during normal ILI runs (targeted at the rigid steel pipeline) where the tool passes through an unbonded flexible pipe. It is apparent that by combining knowledge in ILI technology (limits of detection) and unbonded flexible pipes (structure/failure mechanisms), valuable data is available, and therefore certain assessments can be completed.
The primary information obtained was related to the end-fitting to flexible pipe-layer transition, carcass pitching and internal surface condition. The potential defects and relevant risks from the data can be assessed effectively, for example, in terms of irregular distances for the carcass pitching and spacing between the interlocked wraps, geometric anomalies of the inner diameter (ovalities, dents, etc.) with reference to relevant locations. The data can reveal very important information related to local carcass stress, etc., and can further help identify the possible root causes of damage from external loadings. Examples of external loading are gross tension, bending, torsion, external pressure collapse, or abnormal loadings due to external crushing and impact damage. In addition, depending on available data and the type of technology, we may also be able to assess the transition through the end fitting, the location of external structural features e.g. Mid Water Arch (MWA) clamp, the location of the bend stiffener, etc.
This paper will discuss the development of assessment processes that will allow operators to maximize the value of data collected by existing tools. Furthermore, it will investigate tool and sensor technologies, which – when combined with appropriate assessment methods – will provide more data to help with risk-based integrity management of unbonded flexible pipe.