New Advances in Flexible Riser Monitoring Techniques Using Optical Fiber Sensors

2012 ◽  
Author(s):  
Sérgio R. K. Morikawa ◽  
Arthur M. B. Braga ◽  
Claudio S. Camerini ◽  
Carla C. Kato ◽  
Roberth A. Llerena ◽  
...  
Keyword(s):  
Structural Damage ◽  
Laboratory Tests ◽  
Failure Modes ◽  
Fiber Optic ◽  
Gas Production ◽  
Strain Sensors ◽  
Brazilian Coast ◽  
Outer Sheath ◽  
Flexible Pipes ◽  
Flexible Risers

Petrobras oil and gas production in the deep and ultra deepwater fields in Campos Basin and other provinces off the Brazilian coast heavily relies on flexible pipes. Maximizing the availability and reliability of an extensive offshore pipeline network poses innumerous challenges to the Company, which is steadily moving towards a condition based approach to maintenance of their flexible risers. In this context, Petrobras, in cooperation with its academic partners, has launched a comprehensive R&D program named MONFLEX, focusing on novel techniques for structural monitoring of flexible risers. Years of field experience have demonstrated that one of the most frequent failure modes of flexible pipes is the sequential rupture of wires in their tensile armor layers [1]. The MONFLEX Program has explored a range of different technologies in order to timely detect and monitor the growth of this class of progressive structural damage. Some of the proposed approaches have relied on video cameras pointed towards fixedly mounted targets on the riser outer sheath, vibration and acoustic methods, these in a wide frequency range, and techniques based on fiber optic strain sensors. All three have been experimentally deployed in the field and are currently being evaluated. Among those, fiber optic monitoring is the one that has shown the better promise of becoming the chosen method for detecting wire ruptures in the riser’s armor layers. The fiber optic based monitoring system developed in the MONFLEX R&D Program has been named MODA, which, in Portuguese, stands for Direct Wire Optical Monitoring. The MODA system consists in instrumenting all the wires of the riser’s external tensile armor layer with fiber Bragg grating strain sensors. In flexible risers already in operation, a window in the polymeric outer sheath of the pipe is temporarily opened in order to allow the sensors installation, and then repaired with a protective, anticorrosive layer. Even though in MODA the strain sensors are installed in the external armor layer, full scale laboratory tests have demonstrated that the algorithm employed to treat and analyze the real time data provided by the system is capable of instantaneously detecting ruptures of wires either in the external or internal layers of the tensile armor. The proposed contribution will report the later results of extensive laboratory tests and field trials performed with the MODA system.

Whistling of Pipes With Narrow Corrugations: Scale Model Tests and Consequences for Carcass Design

2013 ◽  
Author(s):  
Joachim Golliard ◽  
Stefan Belfroid ◽  
Erik Bendiksen ◽  
Casper Frimodt
Keyword(s):  
Prediction Model ◽  
Gas Production ◽  
Scale Model ◽  
Small Scale ◽  
Operational Conditions ◽  
Flexible Pipes ◽  
Cavity Opening ◽  
Flexible Risers ◽  
Onset Velocity ◽  
Operational Envelope

Pipes for gas production and transport with a corrugated inner surface, as used in flexible pipes, can be subject to Flow-Induced Pulsations when the flow velocity is larger than a certain velocity. This onset velocity is dependent on the geometry of the corrugations, the operational conditions and the geometry of the topside and subsea piping. In this paper, small-scale tests performed on corrugated tubes are reported. The tested geometries include both “classical” profiles, similar to the inner profile of agraff flexible risers, and profiles with less typical variations, such as narrower and/or deeper cavities, or irregular pitch. These tests were performed in order to evaluate the validity of a prediction model developed earlier for the onset of pulsations, for corrugated pipes with these kinds of atypical variations, which are found on a new type of carcass designs. The mechanism of Flow-Induced Pulsations in corrugated pipes is discussed, as well as the principle of the prediction model. The experimental results show that the validity of the model remains reasonable in most cases, except when the cavities are very narrow. In this case, the model becomes overly conservative. This limitation can be attributed to the fact that, for very narrow cavities, the cavity opening becomes too small compared to the boundary-layer momentum thickness, effectively destroying any instability of the shear layer. Furthermore, the shift towards higher frequencies of the acoustic source term due to narrower cavities, and the possible coupling with higher acoustic modes, is considered. The results of the analysis are used to evaluate the onset velocity and whistling behavior of a newly developed carcass design of flexible risers. A previous analysis has indicated that the particular geometry profile of the new design improves the whistling behavior by pushing the onset velocity outside the typical operational envelope of flexible risers. The analysis confirms that the new design will be less prone to whistling than flexible risers with classical agraff carcasses.

Wear of Outer Sheath Materials in Flexible Pipes: Testing Methodology

2017 ◽  
Author(s):  
Einar Øren ◽  
Marit Larsen ◽  
Frode Andres Kvilhaug ◽  
Bjørn Melve
Keyword(s):  
Measurement Method ◽  
Wear Test ◽  
Test Apparatus ◽  
Comparative Tests ◽  
Test Methodology ◽  
Outer Sheath ◽  
Flexible Pipes ◽  
Pin On Disc ◽  
Flexible Risers ◽  
Arch Support

Outer sheath wear of polymers in flexible risers has been experienced with risers anchored with guide tubes and bellmouths. In addition, wear damages have been observed at touch down points and on subsea arch support structures. A wear test methodology was developed with the purpose to mimic the observations from pipes in operation. The test apparatus used was similar to a pin-on-disc measurement method, but with emphasis on reproducing the exact environment and temperature. Comparative tests have been done between different materials, and for some conditions the differences are significant.

Carcass Failures in Multilayer PVDF Risers

2013 ◽  
Author(s):  
Knut-Aril Farnes ◽  
Claus Kristensen ◽  
Steinar Kristoffersen ◽  
Jan Muren ◽  
Nils Sødahl
Keyword(s):  
Failure Modes ◽  
Load Model ◽  
Flexible Pipes ◽  
Flexible Risers

Statoil have experienced failures in a number of flexible risers due to collapse, overload, tearing and unspiraling of the carcass in pipe structures with multi-layer PVDF pressure barrier. The paper will discuss the carcass failure modes that are characteristic for multilayer flexible pipes with particular focus on the failures due to carcass tearing. The nature of the carcass tearing problem is explained and suggestions for load model and operational policy for mitigation risk of new failures is presented.

Increased safety and improved operation of pipelines with integrated condition sensing in flexible risers and flowlines

2014 ◽  
Vol 54 (1) ◽  
pp. 295 ◽  
Author(s):  
Bo A. Andersen
Keyword(s):  
Condition Monitoring ◽  
Failure Modes ◽  
Optimum Level ◽  
Steel Pipes ◽  
Offshore Production ◽  
Flexible Pipes ◽  
Accurate Picture ◽  
Maximum Period ◽  
Integrity Management ◽  
Flexible Risers

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.

Qualified Assessment for Lifetime Extension of Flexible Risers

2015 ◽  
Author(s):  
Bernt J. Leira ◽  
Svein Are Løtveit ◽  
Stig Berge ◽  
Dag Fergestad ◽  
Nina Langhelle
Keyword(s):  
Flexible Riser ◽  
Term Operation ◽  
Integrity Assessment ◽  
Design Life ◽  
Outer Sheath ◽  
Flexible Pipes ◽  
Flexible Risers ◽  
Lifetime Extension

There have been many challenges with respect to long term operation of flexible pipes, in many cases with the need to replace or repair them before the end of the initial design life. The number of identified failure mechanisms and observed failure events is also increasing. In the present paper, some typical issues that arise during the process of integrity assessment and qualification for lifetime extension are outlined. More detailed considerations are illustrated in relation to a particular case study. This involves elaboration of the different steps which are required in order to be able to extend the lifetime of a flexible riser for the case of corrosive annulus environments. The particular case of an outer sheath damage is applied for the purpose of illustration.

On the Whistling of Corrugated Pipes With Narrow Cavities

2013 ◽  
Author(s):  
Joachim Golliard ◽  
Stefan Belfroid ◽  
Nestor Gonzalez Diez ◽  
Erik Bendiksen ◽  
Casper Frimodt
Keyword(s):  
Source Term ◽  
Gas Production ◽  
Small Scale ◽  
Acoustic Source ◽  
Operational Conditions ◽  
Flexible Pipes ◽  
Inner Surface ◽  
Flexible Risers ◽  
Onset Velocity ◽  
Cavity Width

Pipes with a corrugated inner surface, as used in flexible pipes for gas production and transport, can be subject to Flow-Induced Pulsations when the flow velocities are higher than a certain onset velocity. The onset velocity for classical corrugated pipes can be predicted on basis of the geometry of the corrugations, the operational conditions and the geometry of the topside and subsea piping. A newly developed inner carcass design for flexible pipes features smaller corrugation cavities. The effect of narrow cavities on the whistling of corrugated cavities is evaluated. In this paper, small-scale tests performed on corrugated tubes are reported. The tested geometries include both “classical” profiles, similar to the inner profile of agraff flexible risers, and profiles with less typical variations, such as deeper and narrower cavities. These tests were performed in order to evaluate the validity of a prediction model for the onset of pulsations, for corrugated pipes with these kinds of atypical variations. The experimental results show that the validity of the model remains reasonable, except when the cavities are very narrow. In this case, the model becomes overly conservative. The deviation is attributed to the momentum thickness of the boundary layer, which is too large compared to the cavity width. In this case, any instability of the shear layer is destroyed, which prevents whistling. Furthermore, the shift towards higher frequencies of the acoustic source term due to narrower cavities, and the possible coupling with higher acoustic modes, are considered.

Operators Experience With Flexible Risers

2002 ◽  
Author(s):  
Gudmund Per Olsen ◽  
Ketil Rongved
Keyword(s):  
Failure Modes ◽  
Lifetime Prediction ◽  
Norsk Hydro ◽  
The Future ◽  
Flexible Risers

Norsk Hydro has more than 150 flexible dynamic risers and service lines in operation. Norsk Hydro’s experience with flexible risers started in 1987 when Petrojarl 1 commenced test production at the Oseberg Field. The paper tells the story about Norsk Hydro’s experience through the 15 years of trials with a new and complicated product. This paper will focus on “what went wrong”. This may seem unfair to the product! However, without flexibles we would probably not have seen such successful field developments as the Troll B and C, Njord, Visund and Snorre B. Challenging production and installation schemes have been put forward and fulfilled. However, hopefully this paper can give an insight in failure modes, and so forth give input to enhanced solutions in order to avoid similar situations in the future. This paper gives an overview over the different approaches which have been taken to give a better qualification of the lifetime prediction of the risers. Some of the specific projects will be presented in detail in other papers on this conference.

Self-monitoring Properties of Concrete Columns with Embedded Cement-based Strain Sensors

2011 ◽  
Vol 22 (2) ◽  
pp. 191-200 ◽  
Author(s):  
Huigang Xiao ◽  
Hui Li ◽  
Jinping Ou
Keyword(s):  
Cyclic Load ◽  
Failure Modes ◽  
Concrete Structures ◽  
Concrete Columns ◽  
Strain Sensors ◽  
Strain Sensing ◽  
Self Monitoring ◽  
Good Strain ◽  
Displacement Transducers ◽  
Monotonic Load

Cement-based strain sensors (CBCC sensor) were fabricated by taking the advantage of piezoresistivity of CB-filled CBCC. CBCC sensors were centrally embedded into concrete columns (made with C40 and C80 concretes, respectively) to monitor the strain of the columns under cyclic load and monotonic load by measuring the resistance of CBCC sensors. The comparison between the monitored results of CBCC sensors and that of traditional displacement transducers indicates that CBCC sensors have good strain-sensing abilities. Meanwhile, CBCC sensors exhibit different failure modes that break later than C40 concrete columns, but a little earlier than C80 concrete columns. Therefore, the strength-matching principle between embedded CBCC sensors and concrete columns is proposed in this article to guarantee the sensing capacity of CBCC sensors in various concrete structures. The analytical results agree well with the experimental phenomena.

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