With the increasing use of flexible pipe technology - driven by the move to deeper, more marginal and more challenging conditions - the need for systematic management of the flexible pipes is becoming more apparent. In particular, the full implementation of Riser Integrity Management (RIM) plays a vital role to ensure an efficient and safe operation. This paper will discuss issues regarding Riser Integrity Management raised by operators and addressed to NKT Flexibles (NKTF) as the supplier. The discussion will include measurements and tests of flexible pipes, assessment and repair of possible damages, as well as assessment of change of regime e.g. change of location/ bore contents/ pressure/ temperature/ souring. Riser condition monitoring and inspection form an important part of integrity management together with processing and analyses of the monitored data. The present paper identifies and discusses available and emerging options for condition monitoring and for engineering assessments and remedial actions, and discusses the recently developed technology of embedded optical fiber monitoring for quantifying the integrity of the flexible risers during their service life. Introduction Early Flexible Pipe Development The development and use of flexible riser and pipeline technology for offshore oil and gas production is relatively young, however, flexible pipelines were applied for other purposes, before the introduction to the offshore industry. The concept of a flexible armored marine pipeline was first introduced and applied at a significant scale in the World War II project codenamed PLUTO (PipeLine Under The Ocean) for transporting fuel under the British Channel from the United Kingdom to Normandy, France. The design was based on high voltage marine power cable technology. The first commercial marine pipeline was installed between two Danish islands in 1964, also based on marine power cable technology. The step on to high pressure pipelines, reinforced against collapse, for the offshore industry was taken in 1972, applying technologies developed by IFP, France. Early Experiences Initially, flexible pipelines have been considered maintenance free and not in need for regular inspection. Since their first introduction, a vast number of improvements have been introduced to the design and manufacturing of the pipes, end-terminations and accessories.
The scope of this paper is to present the results from full scale testing of a flexible riser equipped with embedded sensors for distributed temperature sensing. Testing includes monitoring of accessories mounted on the riser, monitoring of hot spots such as trenched sections of the riser, and finally detection of breaches of the outer sheath. Furthermore, the applications of such a condition monitoring system within Riser Integrity Management (RIM) and production optimization will be discussed. For example, the temperature may be measured along a riser (or flowline) for evaluating the annulus environment and as a supplement to the flow assurance assessment, e.g. to avoid hydrate formation. MotivationWith the increasing use of flexible pipe technology -driven by the move of new offshore fields to deeper, more marginal and more challenging conditions -the need for systematic management of the flexible pipes is becoming more apparent. In particular, the full implementation of Riser Integrity Management (RIM) plays a vital role to ensure an efficient and safe operation. Riser condition monitoring and inspection form an important part of integrity management together with processing and analysis of the monitored data. In that respect, the recently developed technology within optical fiber monitoring offers unique possibilities for quantifying the integrity of the flexible risers during their service life. The advantage of an embedded monitoring system is the ability to continuously survey the riser condition, thus enabling operators to detect potential damages in due time. The embedded system will allow monitoring in critical areas (e.g. under a bend stiffener or inside an I-tube) where access is limited for externally mounted monitoring systems.
Unbonded flexible risers are a critical part of offshore field architecture bringing oil and gas from seabed to platforms on the surface. A failure in operation will result in stop of production and hence a significant loss of revenue. Risers are subject to a number of loading issues including internal and external pressure, vessel motions and current and wave actions. As a result, risers, endure significant strain levels which can impact on their integrity and functionality. The recent implementation of fiber optic monitoring embedded in flexible risers, is an important step towards turning risers into inspectable structures. The embedded monitoring systems ensure the asset can operate safely at its optimum level for the maximum period of time. The combined use of optical point sensors and fully distributed sensors allow various events to be monitored. This includes breach of outer sheath, condensate build up, polymer temperature, pipe temperature during shut in, fatigue and wire break. The traditional industry method for combating these issues has been extensive onshore testing on small sections of the riser allowing the operator to build up a bank of fatigue and reliability data which is used to statistically forecast the strains and stresses the riser will encounter. This data takes into account expected changes throughout the lifecycle of the riser, such as material degradation and environmental issues including storms and hurricanes. The main inspection method in operation to back this up has been expensive inspection campaigns by diver or ROV focusing on external damage. New advances in optical technology and riser manufacturing techniques mean that a suite of real-time monitoring can provide a far more accurate picture of a riser's condition during operation. This improves decision making by allowing structural and temperature issues to be detected at the earliest possible stage and rectified in the most efficient manner, ensuring risers satisfy safety and regulatory requirements and help maximize oilfield productivity. The enabled condition dependent maintenance of risers will reduce the need for expensive ROV operations for inspection. Real time riser monitoring is set to play an increasingly important role as the operators start to insist on the adoption of this technology in the risers delivered to them. As oil production reaches into deeper and deeper water depths, the real time understanding of the integrity of the risers will become paramount. This paper details the advances that have been made in optical monitoring and visualization techniques and their application within the intelligent riser.
Continuous condition monitoring of offshore production installations is a vital part of integrity management to ensure safe operation of the asset at its optimum level for the maximum period of time. The recent implementation of fiber-optic condition monitoring embedded into the structures of flexible risers and flowlines is an important step towards turning flexible pipelines into inspectable structures. Embedded sensors enable a suite of monitoring options for both real-time response and long-term changes, which can provide a highly accurate picture of a pipeline’s condition during operation. In this paper the author reports the results from extensive full-scale testing on flexible pipes instrumented with sensors, conducted in cooperation with a major operator. The testing includes detection of a breach of the outer sheath with ingress of seawater into the annulus, remote monitoring of the location of accessories mounted on the pipe—such as buoyancy modules—monitoring of the temperature at a buried section of a pipe in the seabed, identification of hotspots, detection of breaks of tensile armor wires, and monitoring of accumulated fatigue damage in tensile armor wires during operation. Reported failure modes from flexible pipes in operation are briefly discussed to show that the major failure modes reported across all operators through the years are covered by the NOV integrated sensing systems. The detection of structural and temperature issues with integrated condition sensing in flexible pipelines will allow operators to satisfy requirements for periodic inspection, which for rigid steel pipes is performed with intelligent pigging.
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