Project Aims
Inspection and assessment of flexible risers or pipelines on offshore facilities is required to satisfy both regulatory and safety requirements. Typically this is done at a basic level because of a lack of assessment methodologies and inspection techniques suited to these complex components.

Recognising this, the oil and gas industry has developed API Spec 17J which sets minimum standards for the design, specification, manufacture and testing of flexible pipe. A recommended practice was also prepared giving guidelines based on current best practices. The guideline (Guidelines for Integrity Monitoring of Unbonded Flexible Pipes) emphasises the need to collect data during the life of a pipeline/riser asset and the means to store and analyse the data.

FLEXSENS aims to provide this through the development of an intelligent Integrity Management System for flexibles.

The aim of the FLEXSENS project is to demonstrate that the key assessment and inspection technologies can be integrated such that pipeline designers and operators can make informed decisions on the maintenance and inspection requirements for their flexible assets (in particular risers).

To do this the project brought together the most up-to-date developments in sensing of flexible pipe with the best knowledge of design, failure mode assessment and integrity management strategy for flexible pipe systems. The complete system was then evaluated under a number of simulated riser fault conditions to both demonstrate the potential of an integrated inspection and assessment system to pipeline operators and to identify problems and issues which might affect the uptake of the technology by industry.

Project Partners

BHRSolutions provided fluid flow and pipeline pigging technology and test facilities.

CorrOcean Limited provided flexible riser inspection and monitoring technology.

MCS International provided pipeline design and integrity assessment knowhow.

Additional contributions were provided by Agip UK Ltd, RST LTD and the Robert Gordon Institute.

The project was also supported by the European Commission's Energie Programme (Project No: OG/229/98/UK/IE).

Integrity Assessment Software
The software is structured into data and rules on:

• pipe design & cross section
• pipe failure modes
• risk targets
• evaluation methods
• failure drivers
• experimental data from acoustic, position and vibration sensing.

The expert system shell codifies the rule base that underpins the Guidelines for Integrity Monitoring of Unbonded Flexible Pipes (based on the API 17J specification).

In essence the expert system performs a risk-based assessment by assigning probability and consequence of occurrence ratings (POR and COR), based on information specified by the user. For each pipe failure mode a risk level is evaluated as a combination of the numerical values assigned to POR and COR.

By means of an embedded decision rule base the expert system suggests an inspection/monitoring decision based on the calculated risk level.

Benefits

• Makes API guidelines easy to use and interpret.
• Makes best use of the judgments of technical specialists.
• Determines the level of inspection needed at any given time.
• Allows operators to anticipate potential failures and take appropriate remedial action.
• Ability to update management strategy based on monitored results.
• Transparent technical audit trial.

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Summary
Project Aim: to demonstrate that current knowledge of assessment strategies can be integrated with physical measuring devices in a combined tool to assist in the development and implementation of inspection strategies for an asset.

Project Partners: BHRSolutions, CorrOcean, MCS International and others, with part funding from the EC.

System Concept: a combination of knowledge-based Integrity Assessment software and modular inspection and measurement devices.

Integrity Assessment Software: structured software comprising a rule base within an expert system shell and embodies the API guidelines.

Riser Inspection Methods: low-cost screening of a range of parameters.

Benefits: easier application of management strategy and API guidelines on integrity assessment.


Flexible Riser Courtesy of Agip UK.

FLEXSENS System Concept
The approach that FLEXSENS takes is to looks at the life cycle of the asset covering design, operation (including changing operating conditions), maintenance, inspection and decommissioning. It will allow an operator to develop strategies (such as what to inspect, and how often) for individual assets and re-assess these as inspection results or asset operations change. The modular nature of the FLEXSENS inspection equipment will ultimately address a wide range of riser performance parameters as shown in Figure 2.

The system is based on two essential components: a software knowledge-based integrity assessment design tool which is used to determine and adapt integrity monitoring strategies and a pig-mounted inspection tool which uses smart sensors to measure changes in key pipeline characteristics.

Riser Inspection Methods
The FLEXSENS concept requires appropriate condition monitoring data to be input over the life of the riser. Sensing and measuring systems are thus part of the overall approach. The ability to carry out relatively low cost screening of a range of parameters relevant to the riser condition is the aim of the sensing and measuring system. The measurement and inspection carried out are listed below:

• Position and movement
• End pull out detection
• Ovality
• Pressure and temperature
• Vibration
• Annulus monitoring
• Leak detection

Some of these have still to be developed.

Each sensing device is an encapsulated module, which is capable of being mounted on standard and existing pipe intervention tools. The module has an intelligent data capture, system control and on board digital processing system. The modules are intended to operate in flexible pipes with internal bores as small as 4". However for the current demonstration programme the tool was tested in 10" flexible pipe.

The initial functionality has focussed on developing some effective screening tools which can quickly indicate changes in important characteristics of a flexible pipe. Figure 5 shows an example where measurements of changes in the profile of a riser can be used, for instance, to indicate loss of buoyancy. As a consequence the types of potential failure and risks have changed.

Any change in these key measures are used to review and amend the strategy originally developed in the Integrity Assessment software.