The Experts below are selected from a list of 72 Experts worldwide ranked by ideXlab platform
A. Stacey - One of the best experts on this subject based on the ideXlab platform.
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Review and Assessment of Fatigue Data for Offshore Structural Components Containing Through-Thickness Cracks
Volume 5: Materials Technology; CFD and VIV, 2008Co-Authors: Y. H. Zhang, A. StaceyAbstract:In recent years, structural integrity management schemes for offshore installations have placed increased reliance on the use of Flooded Member detection (FMD) as the principal inspection method. This method can be routinely employed in a remotely operated vehicle, which enables a large number of Members to be inspected fairly quickly at a much reduced cost compared to using diver operated techniques. However, reliance on FMD for safety assurance requires that welded joints retain sufficient fatigue life and static strength after through-thickness cracking. A comprehensive examination of published work containing data on fatigue lives beyond through-thickness cracking in offshore structures was carried out, resulting in the development of a database of 281 relevant tests. The database was used to perform a statistical assessment of the effects of different testing conditions and geometrical parameters on the remaining fatigue life beyond the occurrence of through-thickness cracking, N3 , which was represented by a parameter Re. Whilst the data showed a large amount of scatter, it was found that Re depends strongly on chord thickness, loading mode, type of joint and testing environment. In some cases, a significant amount of remaining life existed. This was often associated with T-type tubular joints with thin chord thickness under out-of-plane loading and a seawater (with CP) environment. The influence of the relevant parameters on Re is discussed and attributed to their effect on crack shape, stress distribution, cracking location and crack propagation path.Copyright © 2008 by British Crown and TWI Ltd.
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Reliability Based Assessment for Fatigue Integrity Management
Volume 5: Materials Technology; CFD and VIV, 2008Co-Authors: M. Manzocchi, N. Shetty, A. StaceyAbstract:Reliability analysis can be used to assess the risk of structural failure in ageing offshore installations and to subsequently optimise inspection plans. This paper describes the findings of a joint industry project to develop and implement a methodology for system reliability updating based on the results of in-service inspections. The effects of different combinations of inspection techniques, namely Flooded Member detection (FMD) and magnetic particle inspection (MPI), and inspection intervals on the component reliability were examined. Additionally, a case study was performed to demonstrate the system reliability of actual structures with inspection histories. A comprehensive methodology for updating the assessment of system reliability of offshore structures based on in-service inspection results was developed. The methodology allows several important features associated with system reliability, i.e. redundancy, stress redistribution and correlation between the random variables, to be accounted for. The structural reliability is given in terms of an overall reliability for combined fatigue and pushover. The study demonstrated that the methodology may be used to target inspections to those areas of the structure with low fatigue life and low redundancy.© 2008 ASME
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The Effect of Multiple Member Failure on the Predicted Reliability of Fixed Jacket Structures
Volume 5: Materials Technology; CFD and VIV, 2008Co-Authors: D. Sanderson, A. Nelson, A. StaceyAbstract:Current offshore inspection practice relies on the detection of gross damage, such as Flooded Member detection. Such an inspection philosophy relies upon the structure’s ability to withstand gross damage for an inspection interval based on the large reserve factors on the jacket design strength in both the undamaged and damaged conditions. This requires a demonstration of the structure’s strength in all of the possible damaged conditions with the most critical Member removed. However, the load originally carried by the critical Member is redistributed to other neighbouring Members which must consequently have an impact on the design fatigue lives of other Members and increase the probability of more Members failing. Ignoring the effects of stress redistribution due to Member failure could therefore result in under-prediction of the probability of a second Member failing and hence an optimistic prediction of platform reliability. This paper aims to quantify the effects of stress redistribution on the prediction of platform reliability. Stress and ultimate strength analyses were performed on three platforms in 45m water depth with bracing configurations of varying structural redundancies, namely, single diagonal, inverted K and X-braced, to calculate the stress enhancement in all Members due to the individual failure of all other Members. These stress enhancements were input into probabilistic fracture mechanics models to calculate the increase in failure probability of these second Members due to the failure of a first Member. More than 1000 pushover analyses were performed to calculate the ultimate strength of the structures in all single-Member failed conditions and many hundreds of dual Member failed permutations for each jacket. A cross-correlation of the most significant stress redistribution results and pushover results was used to perform platform reliability assessments. The effect of including stress redistribution and dual Member pushover results was shown to reduce the predicted platform reliability for all bracing configurations, mainly due to a number of dual-Member failed conditions that weakened the jackets significantly. It is recommended that, in addition to performing single Member failed pushover analyses, there is a need to assess dual-Member failed conditions that drastically reduce platform strength.Copyright © 2008 by British Crown
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Risk management of through-thickness cracks in offshore fixed structures
1999Co-Authors: J. V. Sharp, A. StaceyAbstract:Despite the increasing number of ageing structures in the North Sea, the overall trend is for the level of inspection to decrease. The increased use of Flooded Member detection and visual techniques in preference to other techniques for in-service inspection of fixed platforms leads to situations where through-thickness cracks (TTCs) may be present in welded components, prior to their detection. TTCs have been observed offshore and in some cases growth of these cracks has led to Member separation. It is important to consider the capacity of welded components containing TTCs in the light of the original design requirements and the redundancy in the overall structure. Equations on the performance of welded joints and Members with TTCs have been derived from limited test data. In practice, such cracks can grow substantially beyond the through-thickness stage, depending on the frequency of inspection. In some joint types (e.g. ring stiffened) it is also known that when TTCs develop the remaining life is less than in conventional joints and the loss in load carrying area is also increased. Cracks in circumferential welds in tubulars, particularly when single-sided, are often only found at the through-thickness stage; data on the performance of this type of cracked joint are very limited. The implications on structural integrity of these factors are assessed. There is limited information on the effect of TTCs on the structural integrity of welded joints in frame structures. Additionally, it is important to note that the repair of components with TTCs requires a considerable amount of preparation time. Consequently, the integrity of the platform may be at risk for the duration of the repair. Overall, the extensive use of Flooded Member detection requires careful consideration of the additional risk factors arising from the presence of TTCs in components.
J Pearson - One of the best experts on this subject based on the ideXlab platform.
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A novel ultrasonic inspection system for Flooded Member detection offshore
Insight, 1996Co-Authors: D. G. Stirling, Gordon Hayward, J PearsonAbstract:The demand for oil and gas resources has led the search and recovery offshore, encountering in the process some of the most inhospitable working environments. The large structures employed to extract the hydrocarbons have to withstand very severe operating conditions, such as fatigue and corrosion. Consequently, there are regulatory guidelines regarding the monitoring of structural integrity for continuous safe operation. The size of installations and the cost of implementing work offshore have led to the requirement for fast and reliable inspection techniques to provide the necessary data on structural integrity. One ofthose techniques is Flooded Member Detection (FMD), which involves the detection of water in normally air-filled Members of steel jacket installations. Confirmation of water indicates the presence ofa through wall defect in that particular section of the structure. This paper presents on overview of the work involved in the design, development and trial implementation of a prototype ultrasonic FMD tool. The system is based around a multi-frequency ultrasonic array incorporating 1-3 connectivity ceramic/epoxy transducers, The system also comprises a data acquisition and analysis package linked to an expert knowledge base to provide automatic analysis of the ultrasonic data generated by the array.
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An intelligent ultrasonic inspection system for Flooded Member detection in offshore structures
IEEE transactions on ultrasonics ferroelectrics and frequency control, 1993Co-Authors: Gordon Hayward, J Pearson, G. StirlingAbstract:An ultrasonic system for automatic underwater inspection of steel jacket offshore installation is described. It is based on the unambiguous detection of water ingress in normally sealed tubular Members, thereby providing an indication of through-wall structural failure. A novel transducer design, based on a dual frequency array of 1-3 connectivity thickness drive transducers, is used to provide the required sensitivity and act also as an environmental monitor for input to an expert system, which performs automatic data analysis. Although intended primarily for operation on a remotely operated vehicle, the system may be employed satisfactorily by a driver. A series of test trials is described, and the prototype is shown to perform very well for all intended modes of operation. >
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Evaluation of a novel ultrasonic technique for reliable detection of Flooded Members in offshore installations
Ultrasonics Symposium, 1991. Proceedings., IEEE 1991, 1991Co-Authors: G. Stirling, Gordon Hayward, J PearsonAbstract:Flooded Member detection (FMD) of offshore oil installations involves the detection of sea water in normally air-filled structural Members of steel jacket installations. The design and trial implementation of a prototype FMD tool, based around a multi-frequency ultrasonic array, incorporating composite transducer technology and providing data analysis using an expert system are described. Problems associated with more conventional ultrasonic techniques are discussed and improvements offered by the new system are highlighted with a series of operational trials. The tool has a novel ultrasonic array which provides improved efficiency over conventional sensors, and a multi-transducer feature permits identification of corrosion and bad contact conditions generally encountered
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IMPROVED ULTRASONIC Flooded Member DETECTION FOR INSPECTION OF OFFSHORE STRUCTURES
Ultrasonics International 91, 1991Co-Authors: G. Stirling, Gordon Hayward, J PearsonAbstract:The maintenance costs for offshore structures are increased as a result of the hazardous operating environment. Consequently, there is a reliance on maintenance and inspection systems which are efficient and reliable with the potential for automation. One such technique which fulfils these criteria is Flooded Member detection (FMD). The identification of water inside previously air-filled tubular structural Members signifies the presence of a through wall defect. An improved Ultrasonic FMD system is described incorporating an array of sensors based on 1-3 composite transducer technology, integrated with an Expert System for automated data interpretation and decision making.
Michael Burdekin - One of the best experts on this subject based on the ideXlab platform.
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Department of Instrumentation and Analytical Science;
2010Co-Authors: Mijarez R. P. Gaydecki, Michael BurdekinAbstract:Abstract: Structural Flooded Member detection of offshore oil platforms involves the detection of seawater in their normally hollow steel crossbeam Members. NDT methods such as ultrasound have been used to inspect for the presence of water in these applications, often in conjunction with remote operating vehicles. Alternatively, a guided wave sensor system is now being developed which can be permanently attached to a sub-sea installation and that can be powered by the action of the seawater. Upon activation the transducer is able to transmit encoded information to monitoring systems at deck level. Present work has focused on the assessment of guided waves and their attenuation not only due to steel joints and distance but also due to leaky waves coupled into surrounded water. Low frequency excitation exhibits lower attenuation depending on the selected mode, however also can be exposed to acoustic interference leading to a poor SNR. A compromise between these factors has been considered in this application for the successful transmission and reception of encoded information. Low power narrow bandwidth chirp signals were employed with 21 kHz PZT transducers to excite axi-symmetric modes in tubes. Experiments have been carried out using excitations of 0.5V and 5V respectively for water loaded steel k-joints scale model of 4mX0.18mX0.007m an
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Continuous structural monitoring of oil rig sub-sea structures for Flooded Member detection using underwater ultrasound
Insight - Non-Destructive Testing and Condition Monitoring, 2007Co-Authors: Rito Mijarez, Patrick Gaydecki, Michael BurdekinAbstract:An underwater ultrasound system for detecting flooding in the hollow sub-sea structures of offshore steel oil rigs is presented. A sensor, attached to a sub-sea structure and powered by seawater, transmits underwater ultrasound chirp -encoded signals to a real-time digital signal processing monitoring system at surface level. Experiments performed using a jointed steel pipe structure I ton in weight, with dimensions of 7 m x 0.5 m x 16 mm, completely immersed in seawater showed excellent performance using a central excitation frequency of 38 kHz, over distances of 100 m.
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Continuous monitoring guided wave encoded sensor for oil rig Flooded Member detection
Insight - Non-Destructive Testing and Condition Monitoring, 2005Co-Authors: Rito Mijarez, Patrick Gaydecki, Michael BurdekinAbstract:Structural Flooded Member detection of offshore oil platforms involves the detection of seawater in their normally hollow steel crossbeam Members. NDT methods such as ultrasound have been used to inspect for the presence of water in these applications, often in conjunction with remote operating vehicles. Alternatively, a guided wave sensor system is now being developed which can be permanently attached to a sub-sea installation and that can be powered by the action of the seawater. Upon activation, the transducer is able to transmit encoded information to monitoring systems at deck level. Present work has focused on the assessment of guided waves and their attenuation not only due to steel joints and distance but also due to leaky waves coupled into surrounded water. Low-frequency excitation exhibits lower attenuation depending on the selected mode, however this can also be exposed to acoustic interference leading to a poor SNR. A compromise between these factors has been considered in this application for the successful transmission and reception of encoded information. Low-power narrow-bandwidth chirp signals were employed with 21 kHz PZT transducers to excite axisymmetric modes in tubes. Experiments have been carried out using excitations of 0.5 V and 5 V respectively for a water-loaded steel k-joints scale model and a cylindrical bridge steel structure with several k-joints. Important results have been attained, moreover in order to reduce acoustic noise a real-time digital signal processing board has been used to perform digital filtering and signal identification.
G. Stirling - One of the best experts on this subject based on the ideXlab platform.
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An intelligent ultrasonic inspection system for Flooded Member detection in offshore structures
IEEE transactions on ultrasonics ferroelectrics and frequency control, 1993Co-Authors: Gordon Hayward, J Pearson, G. StirlingAbstract:An ultrasonic system for automatic underwater inspection of steel jacket offshore installation is described. It is based on the unambiguous detection of water ingress in normally sealed tubular Members, thereby providing an indication of through-wall structural failure. A novel transducer design, based on a dual frequency array of 1-3 connectivity thickness drive transducers, is used to provide the required sensitivity and act also as an environmental monitor for input to an expert system, which performs automatic data analysis. Although intended primarily for operation on a remotely operated vehicle, the system may be employed satisfactorily by a driver. A series of test trials is described, and the prototype is shown to perform very well for all intended modes of operation. >
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Evaluation of a novel ultrasonic technique for reliable detection of Flooded Members in offshore installations
Ultrasonics Symposium, 1991. Proceedings., IEEE 1991, 1991Co-Authors: G. Stirling, Gordon Hayward, J PearsonAbstract:Flooded Member detection (FMD) of offshore oil installations involves the detection of sea water in normally air-filled structural Members of steel jacket installations. The design and trial implementation of a prototype FMD tool, based around a multi-frequency ultrasonic array, incorporating composite transducer technology and providing data analysis using an expert system are described. Problems associated with more conventional ultrasonic techniques are discussed and improvements offered by the new system are highlighted with a series of operational trials. The tool has a novel ultrasonic array which provides improved efficiency over conventional sensors, and a multi-transducer feature permits identification of corrosion and bad contact conditions generally encountered
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IMPROVED ULTRASONIC Flooded Member DETECTION FOR INSPECTION OF OFFSHORE STRUCTURES
Ultrasonics International 91, 1991Co-Authors: G. Stirling, Gordon Hayward, J PearsonAbstract:The maintenance costs for offshore structures are increased as a result of the hazardous operating environment. Consequently, there is a reliance on maintenance and inspection systems which are efficient and reliable with the potential for automation. One such technique which fulfils these criteria is Flooded Member detection (FMD). The identification of water inside previously air-filled tubular structural Members signifies the presence of a through wall defect. An improved Ultrasonic FMD system is described incorporating an array of sensors based on 1-3 composite transducer technology, integrated with an Expert System for automated data interpretation and decision making.
Gordon Hayward - One of the best experts on this subject based on the ideXlab platform.
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A novel ultrasonic inspection system for Flooded Member detection offshore
Insight, 1996Co-Authors: D. G. Stirling, Gordon Hayward, J PearsonAbstract:The demand for oil and gas resources has led the search and recovery offshore, encountering in the process some of the most inhospitable working environments. The large structures employed to extract the hydrocarbons have to withstand very severe operating conditions, such as fatigue and corrosion. Consequently, there are regulatory guidelines regarding the monitoring of structural integrity for continuous safe operation. The size of installations and the cost of implementing work offshore have led to the requirement for fast and reliable inspection techniques to provide the necessary data on structural integrity. One ofthose techniques is Flooded Member Detection (FMD), which involves the detection of water in normally air-filled Members of steel jacket installations. Confirmation of water indicates the presence ofa through wall defect in that particular section of the structure. This paper presents on overview of the work involved in the design, development and trial implementation of a prototype ultrasonic FMD tool. The system is based around a multi-frequency ultrasonic array incorporating 1-3 connectivity ceramic/epoxy transducers, The system also comprises a data acquisition and analysis package linked to an expert knowledge base to provide automatic analysis of the ultrasonic data generated by the array.
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An intelligent ultrasonic inspection system for Flooded Member detection in offshore structures
IEEE transactions on ultrasonics ferroelectrics and frequency control, 1993Co-Authors: Gordon Hayward, J Pearson, G. StirlingAbstract:An ultrasonic system for automatic underwater inspection of steel jacket offshore installation is described. It is based on the unambiguous detection of water ingress in normally sealed tubular Members, thereby providing an indication of through-wall structural failure. A novel transducer design, based on a dual frequency array of 1-3 connectivity thickness drive transducers, is used to provide the required sensitivity and act also as an environmental monitor for input to an expert system, which performs automatic data analysis. Although intended primarily for operation on a remotely operated vehicle, the system may be employed satisfactorily by a driver. A series of test trials is described, and the prototype is shown to perform very well for all intended modes of operation. >
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Evaluation of a novel ultrasonic technique for reliable detection of Flooded Members in offshore installations
Ultrasonics Symposium, 1991. Proceedings., IEEE 1991, 1991Co-Authors: G. Stirling, Gordon Hayward, J PearsonAbstract:Flooded Member detection (FMD) of offshore oil installations involves the detection of sea water in normally air-filled structural Members of steel jacket installations. The design and trial implementation of a prototype FMD tool, based around a multi-frequency ultrasonic array, incorporating composite transducer technology and providing data analysis using an expert system are described. Problems associated with more conventional ultrasonic techniques are discussed and improvements offered by the new system are highlighted with a series of operational trials. The tool has a novel ultrasonic array which provides improved efficiency over conventional sensors, and a multi-transducer feature permits identification of corrosion and bad contact conditions generally encountered
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IMPROVED ULTRASONIC Flooded Member DETECTION FOR INSPECTION OF OFFSHORE STRUCTURES
Ultrasonics International 91, 1991Co-Authors: G. Stirling, Gordon Hayward, J PearsonAbstract:The maintenance costs for offshore structures are increased as a result of the hazardous operating environment. Consequently, there is a reliance on maintenance and inspection systems which are efficient and reliable with the potential for automation. One such technique which fulfils these criteria is Flooded Member detection (FMD). The identification of water inside previously air-filled tubular structural Members signifies the presence of a through wall defect. An improved Ultrasonic FMD system is described incorporating an array of sensors based on 1-3 composite transducer technology, integrated with an Expert System for automated data interpretation and decision making.