Structures of high speed craft must generally satisfy requirements to strength and stiffness for ... more Structures of high speed craft must generally satisfy requirements to strength and stiffness for resisting local and global loads. In addition, classification societies specify minimum thickness of plating that are independent of the design loads. Such requirements are largely experience-based and are intended to provide the structure with a certain resistance to local effects such as impacts and abrasion. For high speed craft built in composite materials, the minimum thickness requirement often dictates the scantlings. The minimum thickness requirements are considered by many to discriminate against novel materials and designs since they are based on experience with conventional practice. A more rational approach based on functional requirements seems desirable. This paper outlines the factors that make it necessary to have local requirements that are additional to those based on explicit calculation of strength and stiffness under specified applied loadings. A simplified approach is proposed. This is based on the use of standardised tests to prove that a design with a new materials or layup has resistance to local abrasive or impact loads that is equivalent to that of a design that has been proven through successful service. For skin laminates of sandwich panels the existing Det Norske Veritas Rules for Classification of High Speed and Light Craft already allow lower thicknesses than those given by the minimum thickness formula, provided that equivalence can be demonstrated. The paper shows how this approach can be put into practice.
Journal of Reinforced Plastics and Composites, Nov 4, 2013
Bonded patch repairs are an efficient repair method for corroded or cracked metal structures, if ... more Bonded patch repairs are an efficient repair method for corroded or cracked metal structures, if welding is inconvenient. Avoiding the fire hazard of welding is a major reason for using patch repairs, but it can also be reduced distortions of the metal parts, protecting heat sensitive materials or equipment near the repair such as cables and so on. The lack of guidelines for performing such repairs has been a major hindrance for using this technology. A new recommended practice ‘Design, Fabrication, Operation and Qualification of Bonded Repair of Steel Structures’ has been published addressing: when a repair can be applied, which failure mechanisms need to be addressed, which material properties are needed, fabrication-related issues and in-service inspection. This paper will give a brief introduction to the document and its application areas.
Historically, successful introduction of new technologies in the offshore oiland gas industry has... more Historically, successful introduction of new technologies in the offshore oiland gas industry has been based on different strategies. With support from theindustry DNV formulated a Recommended Practice (RP) that defined systematicsfor Qualification of New Technology in 2001. Today, it has earned thereputation of an accepted industry practice. Experience gained from 10 years of industry use has been implemented in anupdated RP. The main improvements relate to:Qualification process alignment with business needs.Adaptation to technology development challenges.Facilitation of rapid improvement cycles based on preceding versions of thesame technology.Use of modern methods within systems engineering and dependability. Two industry examples illustrate how the improvements apply to the users of theupdated DNV-RP-A203:Fiber rope technology.Qualification of a new cold-repair technology for offshore units. Introduction This paper presents two case examples where the TQ systematics are of benefit. Then the principles along with the background and motives are summarized, andthe changes made to the DNV-RP-A203 are reviewed. The use of the TQ systematics in various project phases is explained withreference to the case examples. Applicability of evidence from precedingqualification is discussed, addressing how the problems of starting the TQprocess late can be overcome, how to effectively make incremental technologychanges and how to qualify technology for new ways of use. Background Throughout history, new technologies have been developed and used to captureopportunity and solve problems. In the offshore oil and gas industry, newtechnologies allowed oil producers to use floating installations and subseadevelopments to produce in deeper waters. Technologies have been developed andemployed, and then refined such that technologies have evolvedcontinually. However it can be problematic if new solutions are introduced without riskevaluation, or when an unknown service context is encountered. In each case, unanticipated problems may occur. In parallel with modern technology developments, engineering methods have alsodeveloped, most of all in the military, aerospace and nuclear industries. Theobjective was to move from a reactive approach to a proactive approach, aimingto anticipate potential accidents and take precautions for accidents that havenot yet occurred. Traditionally, standards have been written in a prescriptive format providingdetails for acceptable designs. Hence, interpretation of the standard tends tobe straight forward, and it is simple to verify compliance with it. Thepotentially streamlined and predictable processes are an advantage of theprescriptive approach. A disadvantage is - however - that it tends to lock theindustry to specific solutions where innovation and development would bebetter. Another disadvantage is potential application of an inadequate standardin the absence of a standard that covers the technology precisely. Use of astandard that is only partly relevant can allow serious flaws to slip throughthe design reviews. Inadequacy of standards may further threaten the success ofan innovation process, and in the final instance safety is at risk.
ABSTRACT Adhesive bonding offers a simple and efficient way of joining structural components with... more ABSTRACT Adhesive bonding offers a simple and efficient way of joining structural components without weakening them by holes or welding.This article develops a new model to predict the fracture load of bonded overlap joints using a fracture mechanics approach. The bondline fracture resistance and effects of the nonlinear inelastic behaviour of structural adhesives are accounted for separately. For bonded single overlap joint configurations the model is expressed as simple explicit formulas.An experimental programme is presented where the design parameters that a designer can adjust to obtain the desired joint capacity are systematically varied. Comparison of test results with the predictions by current strength-of-materials capacity models highlights disparities between the theoretical predictions and experimental evidence. In contrast, the new model shows good agreement with the experimental results.It should be noted that the simple new formulas apply to a well-defined range of bonded overlap joint configurations and do not purport to apply in general to every other joint configuration.
Proceedings Of The Institution Of Mechanical Engineers, Part M: Journal Of Engineering For The Maritime Environment, Dec 1, 2004
This paper discusses a new approach to dealing with the dilemma that many designers of bonded joi... more This paper discusses a new approach to dealing with the dilemma that many designers of bonded joints face. They cannot demonstrate the required long-term performance of their bonded joints. At the same time there are no practical applications of bonded joints to build up in-service experience of load-carrying adhesively bonded joints in shipbuilding.
: This chapter starts with a brief summary of the use of bonded joints in marine engineering and ... more : This chapter starts with a brief summary of the use of bonded joints in marine engineering and the standards that may apply. Some recommendations for design of bonded joints follow. Since theoretical modelling shows some promise for bonded joints thus designed, this chapter focuses on failure prediction by use of theoretical models of such joints and discusses other bonded joint configurations only briefly. The effects of environmental exposure are briefly discussed. Predictions by a range of theoretical models are compared with experimental results for bonded joints leading to recommendations for failure prediction which allow reliable use of failure prediction in the design of a defined range of bonded joint configurations.
This chapter addresses bolt-adhesive joints to transfer both loads and moments. All our examples ... more This chapter addresses bolt-adhesive joints to transfer both loads and moments. All our examples are taken from maritime applications. Experience has shown that bolt-adhesive joints in the maritime industry are not designed for hybrid action where one joining method improves the performance of the other. Rather they are used in a fail-safe-mode where one joining method takes over should the
New technologies typically involve innovative aspects that are not addressed by the existing norm... more New technologies typically involve innovative aspects that are not addressed by the existing normative standards and hence are not assessable through common certification procedures. To ensure that new technologies can be implemented in a safe and reliable manner, a specific kind of assessment is performed, which in many industries, e.g., the energy sector, is known as Technology Qualification (TQ). TQ aims at demonstrating with an acceptable level of confidence that a new technology will function within specified limits. Expert opinion plays an important role in TQ, both to identify the safety and reliability evidence that needs to be developed, and to interpret the evidence provided. Hence, it is crucial to apply a systematic process for eliciting expert opinions, and to use the opinions for measuring the satisfaction of a technology's safety and reliability objectives. In this paper, drawing on the concept of assurance cases, we propose a goal-based approach for TQ. The approach, which is supported by a software tool, enables analysts to quantitatively reason about the satisfaction of a technology's overall goals and further to identify the aspects that must be improved to increase goal satisfaction. The three main components enabling quantitative assessment are goal models, expert elicitation, and probabilistic simulation. We report on an industrial pilot study where we apply our approach for assessing a new offshore technology.
Weight-critical marine structures, such as high-speed craft, are often made of high-strength alum... more Weight-critical marine structures, such as high-speed craft, are often made of high-strength aluminium, and the usual joining method is welding. To improve the performance of high-speed craft there is a tendency to seeking lighter weight materials, especially in parts of the structure where weight-saving is particularly beneficial, such as in the superstructure. Light-weight materials can be fibre-reinforced composites. When joining
Composites Part A-applied Science and Manufacturing, Sep 1, 2009
On ships, tankers and similar vessels structural defects such as cracks and corrosion damage are ... more On ships, tankers and similar vessels structural defects such as cracks and corrosion damage are typically repaired by welding. However, welding is unwanted hotwork on floating offshore units (FOUs) such as floating, production, storage and offloading (FPSO) and floating, storage and offloading (FSO) vessels because it requires shutdown of parts of the vessel thus resulting in expensive production delays. Bonded fibre composite material patch repairs can be used as an alternative to overcome the hazards of hotwork associated with welding. The patches are bonded over the defect and the integrity of the original structure is hence restored. The patch repair technology can also be utilised to provide upgrades, such as life extensions and higher design requirements. A recommended practice (RP) has been developed that describes requirements for patch repairs used in FOUs. To provide flexibility and to fit different repair needs, the RP defines a range of Repair Classes that can be used depending on the urgency of the repair and the need for optimisation. The qualification effort increases with the degree of optimisation. The requirements are based on an extensive test program carried out in the laboratory (reported elsewhere) as well as experience from full-scale repair demonstrators. Two full-scale repair demonstrators were carried out on actual FOUs to demonstrate the feasibility of the RP for bonded composite patch repair. In addition the demonstrators also showed the viability of using bonded composite repairs under harsh conditions encountered in oil and gas exploration and production environments. The first repair was carried out to arrest a fatigue crack that had developed from the corner of a door, while the second repair was carried out to restore material loss on a heavily pitted deck floor. Both repair cases are used as examples to demonstrate the proposed qualification procedures whilst at the same time discussing the challenges and potential applications of this patch repair technology for FOUs in the oil and gas industry.
This paper shows work performed through a Joint Industry Project (JIP), aimed to enable repairs m... more This paper shows work performed through a Joint Industry Project (JIP), aimed to enable repairs made from composite materials to be applied to metallic structural components of offshore platforms in general and FPSOs in particular. The basic motivation was to provide a repair methodology that would cause a reduced impact to platform operations, particularly in classified areas. The focus on FPSOs derived from the fact that most of them are converted tankers, originally designed for overhauling in suitable docks from time to time. That is no longer possible once they are deployed as floating platforms, intended to stay in place for twenty years or more. An important prerequisite was that the repair procedure had necessarily to have the approval of the Classification Society of the platform. The project was conducted in three phases. The objective of the first phase was to develop a qualification procedure for the repair of relevant defects with adhesive patches and to demonstrate its feasibility with simple examples. Along phase two a Project Recommended Practice for Patch Repair was issued and more qualification tests were performed. Phase three consisted of a practical application of the Recommended Practice, accomplished within Petrobras by a repair at a ballast tank of the production semisubmersible platform P-20, in operation at Campos basin. The repair was accomplished by means of carbon fiber reinforcements within a vinylester matrix. This paper describes the P-20 repair case and the design of the bonded repair. A brief overview is presented of the installation of the repair, quality assurance issues and needs for future follow-up. The experimental and theoretical studies performed in support of the repair trial are briefly described. The successful repair trial demonstrates the utility of bonded repairs in managing the integrity of offshore steel structure assets. Introduction This paper shows the result of several years of research aimed to develop a cold repair technology for marine structures based on bonding of composite materials. The main objective was to minimize impact on the operational routine of a floating production platform, even if the repair takes place in a classified area. The work was done by means of a Joint Industrial Project (JIP) coordinated by Det Norske Veritas (DNV). The sponsors of the JIP were Petrobras, Petronas, Statoil, Norsk Hydro, Shell and ConocoPhillips. The role DNV plays on the usage of composite materials in offshore is well known, through the documentation it already produced on the subject. DNV is also the Classification Society of some production platforms in Brazil, making it easier to have the necesssary approval for a field trial of the technology.
The paper discusses how large-deflection theory forms the basis of the strength and deflection re... more The paper discusses how large-deflection theory forms the basis of the strength and deflection requirements for FRP single-skin laminates in the High Speed and Light Craft Rules of Det Norske Veritas (DNV). In the current version of the DNV rules the restrictions set for allowable deflections limit the benefits of using a non-linear formulation. The paper examines the benefits of using a non-linear formulation within the current deflection limits, and the potential benefits of relaxing these limits. The current non-linear formulation is evaluated and compared with non-linear finite element calculations.
A new standard for site-specific design of free fall lifeboats has been developed, aiming at prov... more A new standard for site-specific design of free fall lifeboats has been developed, aiming at providing for sufficiently safe lifeboat designs. The objective has been to develop a standard that follows the same reliability-based safety philosophy and design principles as those implemented and used for design of conventional fixed and floating offshore structures. The standard is intended to cover all aspects involved in the design process for a free fall lifeboat, providing requirements that shall be met in design as well as guidance on how to meet these requirements. The following aspects are covered: Safety philosophy and design principles, metocean conditions, loads, materials, structural design, operational requirements, occupant safety and comfort, model testing and full scale testing, installation, equipment, and qualification of lifeboat concepts. The new standard is published both as an OLF Guideline by the Norwegian Oil Industry Association OLF and as a DNV Offshore Standard, DNV-OS-E406, by Det Norske Veritas. The paper presents the highlights of the new standard with emphasis on topics which are critical for design of free fall lifeboats, first of all structural safety, human safety and comfort, and headway.
This paper reports on a series of tensile pull off tests on Composite T-joints as part of a compr... more This paper reports on a series of tensile pull off tests on Composite T-joints as part of a comprehensive test programme undertaken under the auspices of the EUCLID RTP3.21 project on “Survivability, Durability and Performance of Naval Composite Structures”. The tests have been developed to evaluate joints suitable for use with large composite superstructures i.e. a hangar on a frigate type warship. To assess the performance of these joints under quasi-static and dynamic loading, test procedures have been developed using both shock table facilities and conventional servo-hydraulic test machines. The test procedures are fully complementary to ensure that test results can be directly compared. Test results established that the joint failed within the interface between the base sandwich laminate and the joint overlaminate. As joint assembly is a secondary process this is to be anticipated. Both the dynamic and quasi-static test results showed similar tensile loading performances; for quasi-static testing core shear failure immediately preceded joint failure, whereas no core failure was noted for the dynamic tests. These results suggest that the joint and base sandwich laminate chosen for the EUCLID RTP3.21 project are well matched
The paper describes experimental and numerical techniques to study the structural design and beha... more The paper describes experimental and numerical techniques to study the structural design and behaviour of thick-adherend DLS joints that are based on steel /steel and steel/composites and epoxy adhesives, with focus on long overlap joints. A standard fabrication method was followed to produce 60 specimens of various dimensions and materials.
Oil and gas exploration and exploitation in deep and ultra-deep waters challenges classical riser... more Oil and gas exploration and exploitation in deep and ultra-deep waters challenges classical riser technology and configuration. New technologies, including carbon fiber as composite armors, influence weight and strength of the riser. This can allow for more simple configurations compared with conventional ones, simplifies installation procedures and eventually lead to reduced costs. The new fiber reinforced cross section sheaths requires new analytical models in the local stress analysis tools. The current paper explores efficient and accurate implementations of orthotropic laminate sheaths into classical cross section simulation tools. The model is based on a classic partition of the analysis scheme into a combined load and response model consisting of an axisymmetric and pure bending part. The suggested model is based on full 3D elasticity solution that allows for thick cylindrical laminates taking into account all stress and strain components. The model is compared with 3D Abaqus results for a number of different lay-ups and the results show excellent agreement with the more advanced 3D simulations in both axisymmetric and bending response modes. The laminate, a thermoplastic composite layer with carbon fibers, is used as a component in an unbonded flexible pipe. The cross-sectional analysis is thus performed in the classical way.
Structures of high speed craft must generally satisfy requirements to strength and stiffness for ... more Structures of high speed craft must generally satisfy requirements to strength and stiffness for resisting local and global loads. In addition, classification societies specify minimum thickness of plating that are independent of the design loads. Such requirements are largely experience-based and are intended to provide the structure with a certain resistance to local effects such as impacts and abrasion. For high speed craft built in composite materials, the minimum thickness requirement often dictates the scantlings. The minimum thickness requirements are considered by many to discriminate against novel materials and designs since they are based on experience with conventional practice. A more rational approach based on functional requirements seems desirable. This paper outlines the factors that make it necessary to have local requirements that are additional to those based on explicit calculation of strength and stiffness under specified applied loadings. A simplified approach is proposed. This is based on the use of standardised tests to prove that a design with a new materials or layup has resistance to local abrasive or impact loads that is equivalent to that of a design that has been proven through successful service. For skin laminates of sandwich panels the existing Det Norske Veritas Rules for Classification of High Speed and Light Craft already allow lower thicknesses than those given by the minimum thickness formula, provided that equivalence can be demonstrated. The paper shows how this approach can be put into practice.
Journal of Reinforced Plastics and Composites, Nov 4, 2013
Bonded patch repairs are an efficient repair method for corroded or cracked metal structures, if ... more Bonded patch repairs are an efficient repair method for corroded or cracked metal structures, if welding is inconvenient. Avoiding the fire hazard of welding is a major reason for using patch repairs, but it can also be reduced distortions of the metal parts, protecting heat sensitive materials or equipment near the repair such as cables and so on. The lack of guidelines for performing such repairs has been a major hindrance for using this technology. A new recommended practice ‘Design, Fabrication, Operation and Qualification of Bonded Repair of Steel Structures’ has been published addressing: when a repair can be applied, which failure mechanisms need to be addressed, which material properties are needed, fabrication-related issues and in-service inspection. This paper will give a brief introduction to the document and its application areas.
Historically, successful introduction of new technologies in the offshore oiland gas industry has... more Historically, successful introduction of new technologies in the offshore oiland gas industry has been based on different strategies. With support from theindustry DNV formulated a Recommended Practice (RP) that defined systematicsfor Qualification of New Technology in 2001. Today, it has earned thereputation of an accepted industry practice. Experience gained from 10 years of industry use has been implemented in anupdated RP. The main improvements relate to:Qualification process alignment with business needs.Adaptation to technology development challenges.Facilitation of rapid improvement cycles based on preceding versions of thesame technology.Use of modern methods within systems engineering and dependability. Two industry examples illustrate how the improvements apply to the users of theupdated DNV-RP-A203:Fiber rope technology.Qualification of a new cold-repair technology for offshore units. Introduction This paper presents two case examples where the TQ systematics are of benefit. Then the principles along with the background and motives are summarized, andthe changes made to the DNV-RP-A203 are reviewed. The use of the TQ systematics in various project phases is explained withreference to the case examples. Applicability of evidence from precedingqualification is discussed, addressing how the problems of starting the TQprocess late can be overcome, how to effectively make incremental technologychanges and how to qualify technology for new ways of use. Background Throughout history, new technologies have been developed and used to captureopportunity and solve problems. In the offshore oil and gas industry, newtechnologies allowed oil producers to use floating installations and subseadevelopments to produce in deeper waters. Technologies have been developed andemployed, and then refined such that technologies have evolvedcontinually. However it can be problematic if new solutions are introduced without riskevaluation, or when an unknown service context is encountered. In each case, unanticipated problems may occur. In parallel with modern technology developments, engineering methods have alsodeveloped, most of all in the military, aerospace and nuclear industries. Theobjective was to move from a reactive approach to a proactive approach, aimingto anticipate potential accidents and take precautions for accidents that havenot yet occurred. Traditionally, standards have been written in a prescriptive format providingdetails for acceptable designs. Hence, interpretation of the standard tends tobe straight forward, and it is simple to verify compliance with it. Thepotentially streamlined and predictable processes are an advantage of theprescriptive approach. A disadvantage is - however - that it tends to lock theindustry to specific solutions where innovation and development would bebetter. Another disadvantage is potential application of an inadequate standardin the absence of a standard that covers the technology precisely. Use of astandard that is only partly relevant can allow serious flaws to slip throughthe design reviews. Inadequacy of standards may further threaten the success ofan innovation process, and in the final instance safety is at risk.
ABSTRACT Adhesive bonding offers a simple and efficient way of joining structural components with... more ABSTRACT Adhesive bonding offers a simple and efficient way of joining structural components without weakening them by holes or welding.This article develops a new model to predict the fracture load of bonded overlap joints using a fracture mechanics approach. The bondline fracture resistance and effects of the nonlinear inelastic behaviour of structural adhesives are accounted for separately. For bonded single overlap joint configurations the model is expressed as simple explicit formulas.An experimental programme is presented where the design parameters that a designer can adjust to obtain the desired joint capacity are systematically varied. Comparison of test results with the predictions by current strength-of-materials capacity models highlights disparities between the theoretical predictions and experimental evidence. In contrast, the new model shows good agreement with the experimental results.It should be noted that the simple new formulas apply to a well-defined range of bonded overlap joint configurations and do not purport to apply in general to every other joint configuration.
Proceedings Of The Institution Of Mechanical Engineers, Part M: Journal Of Engineering For The Maritime Environment, Dec 1, 2004
This paper discusses a new approach to dealing with the dilemma that many designers of bonded joi... more This paper discusses a new approach to dealing with the dilemma that many designers of bonded joints face. They cannot demonstrate the required long-term performance of their bonded joints. At the same time there are no practical applications of bonded joints to build up in-service experience of load-carrying adhesively bonded joints in shipbuilding.
: This chapter starts with a brief summary of the use of bonded joints in marine engineering and ... more : This chapter starts with a brief summary of the use of bonded joints in marine engineering and the standards that may apply. Some recommendations for design of bonded joints follow. Since theoretical modelling shows some promise for bonded joints thus designed, this chapter focuses on failure prediction by use of theoretical models of such joints and discusses other bonded joint configurations only briefly. The effects of environmental exposure are briefly discussed. Predictions by a range of theoretical models are compared with experimental results for bonded joints leading to recommendations for failure prediction which allow reliable use of failure prediction in the design of a defined range of bonded joint configurations.
This chapter addresses bolt-adhesive joints to transfer both loads and moments. All our examples ... more This chapter addresses bolt-adhesive joints to transfer both loads and moments. All our examples are taken from maritime applications. Experience has shown that bolt-adhesive joints in the maritime industry are not designed for hybrid action where one joining method improves the performance of the other. Rather they are used in a fail-safe-mode where one joining method takes over should the
New technologies typically involve innovative aspects that are not addressed by the existing norm... more New technologies typically involve innovative aspects that are not addressed by the existing normative standards and hence are not assessable through common certification procedures. To ensure that new technologies can be implemented in a safe and reliable manner, a specific kind of assessment is performed, which in many industries, e.g., the energy sector, is known as Technology Qualification (TQ). TQ aims at demonstrating with an acceptable level of confidence that a new technology will function within specified limits. Expert opinion plays an important role in TQ, both to identify the safety and reliability evidence that needs to be developed, and to interpret the evidence provided. Hence, it is crucial to apply a systematic process for eliciting expert opinions, and to use the opinions for measuring the satisfaction of a technology's safety and reliability objectives. In this paper, drawing on the concept of assurance cases, we propose a goal-based approach for TQ. The approach, which is supported by a software tool, enables analysts to quantitatively reason about the satisfaction of a technology's overall goals and further to identify the aspects that must be improved to increase goal satisfaction. The three main components enabling quantitative assessment are goal models, expert elicitation, and probabilistic simulation. We report on an industrial pilot study where we apply our approach for assessing a new offshore technology.
Weight-critical marine structures, such as high-speed craft, are often made of high-strength alum... more Weight-critical marine structures, such as high-speed craft, are often made of high-strength aluminium, and the usual joining method is welding. To improve the performance of high-speed craft there is a tendency to seeking lighter weight materials, especially in parts of the structure where weight-saving is particularly beneficial, such as in the superstructure. Light-weight materials can be fibre-reinforced composites. When joining
Composites Part A-applied Science and Manufacturing, Sep 1, 2009
On ships, tankers and similar vessels structural defects such as cracks and corrosion damage are ... more On ships, tankers and similar vessels structural defects such as cracks and corrosion damage are typically repaired by welding. However, welding is unwanted hotwork on floating offshore units (FOUs) such as floating, production, storage and offloading (FPSO) and floating, storage and offloading (FSO) vessels because it requires shutdown of parts of the vessel thus resulting in expensive production delays. Bonded fibre composite material patch repairs can be used as an alternative to overcome the hazards of hotwork associated with welding. The patches are bonded over the defect and the integrity of the original structure is hence restored. The patch repair technology can also be utilised to provide upgrades, such as life extensions and higher design requirements. A recommended practice (RP) has been developed that describes requirements for patch repairs used in FOUs. To provide flexibility and to fit different repair needs, the RP defines a range of Repair Classes that can be used depending on the urgency of the repair and the need for optimisation. The qualification effort increases with the degree of optimisation. The requirements are based on an extensive test program carried out in the laboratory (reported elsewhere) as well as experience from full-scale repair demonstrators. Two full-scale repair demonstrators were carried out on actual FOUs to demonstrate the feasibility of the RP for bonded composite patch repair. In addition the demonstrators also showed the viability of using bonded composite repairs under harsh conditions encountered in oil and gas exploration and production environments. The first repair was carried out to arrest a fatigue crack that had developed from the corner of a door, while the second repair was carried out to restore material loss on a heavily pitted deck floor. Both repair cases are used as examples to demonstrate the proposed qualification procedures whilst at the same time discussing the challenges and potential applications of this patch repair technology for FOUs in the oil and gas industry.
This paper shows work performed through a Joint Industry Project (JIP), aimed to enable repairs m... more This paper shows work performed through a Joint Industry Project (JIP), aimed to enable repairs made from composite materials to be applied to metallic structural components of offshore platforms in general and FPSOs in particular. The basic motivation was to provide a repair methodology that would cause a reduced impact to platform operations, particularly in classified areas. The focus on FPSOs derived from the fact that most of them are converted tankers, originally designed for overhauling in suitable docks from time to time. That is no longer possible once they are deployed as floating platforms, intended to stay in place for twenty years or more. An important prerequisite was that the repair procedure had necessarily to have the approval of the Classification Society of the platform. The project was conducted in three phases. The objective of the first phase was to develop a qualification procedure for the repair of relevant defects with adhesive patches and to demonstrate its feasibility with simple examples. Along phase two a Project Recommended Practice for Patch Repair was issued and more qualification tests were performed. Phase three consisted of a practical application of the Recommended Practice, accomplished within Petrobras by a repair at a ballast tank of the production semisubmersible platform P-20, in operation at Campos basin. The repair was accomplished by means of carbon fiber reinforcements within a vinylester matrix. This paper describes the P-20 repair case and the design of the bonded repair. A brief overview is presented of the installation of the repair, quality assurance issues and needs for future follow-up. The experimental and theoretical studies performed in support of the repair trial are briefly described. The successful repair trial demonstrates the utility of bonded repairs in managing the integrity of offshore steel structure assets. Introduction This paper shows the result of several years of research aimed to develop a cold repair technology for marine structures based on bonding of composite materials. The main objective was to minimize impact on the operational routine of a floating production platform, even if the repair takes place in a classified area. The work was done by means of a Joint Industrial Project (JIP) coordinated by Det Norske Veritas (DNV). The sponsors of the JIP were Petrobras, Petronas, Statoil, Norsk Hydro, Shell and ConocoPhillips. The role DNV plays on the usage of composite materials in offshore is well known, through the documentation it already produced on the subject. DNV is also the Classification Society of some production platforms in Brazil, making it easier to have the necesssary approval for a field trial of the technology.
The paper discusses how large-deflection theory forms the basis of the strength and deflection re... more The paper discusses how large-deflection theory forms the basis of the strength and deflection requirements for FRP single-skin laminates in the High Speed and Light Craft Rules of Det Norske Veritas (DNV). In the current version of the DNV rules the restrictions set for allowable deflections limit the benefits of using a non-linear formulation. The paper examines the benefits of using a non-linear formulation within the current deflection limits, and the potential benefits of relaxing these limits. The current non-linear formulation is evaluated and compared with non-linear finite element calculations.
A new standard for site-specific design of free fall lifeboats has been developed, aiming at prov... more A new standard for site-specific design of free fall lifeboats has been developed, aiming at providing for sufficiently safe lifeboat designs. The objective has been to develop a standard that follows the same reliability-based safety philosophy and design principles as those implemented and used for design of conventional fixed and floating offshore structures. The standard is intended to cover all aspects involved in the design process for a free fall lifeboat, providing requirements that shall be met in design as well as guidance on how to meet these requirements. The following aspects are covered: Safety philosophy and design principles, metocean conditions, loads, materials, structural design, operational requirements, occupant safety and comfort, model testing and full scale testing, installation, equipment, and qualification of lifeboat concepts. The new standard is published both as an OLF Guideline by the Norwegian Oil Industry Association OLF and as a DNV Offshore Standard, DNV-OS-E406, by Det Norske Veritas. The paper presents the highlights of the new standard with emphasis on topics which are critical for design of free fall lifeboats, first of all structural safety, human safety and comfort, and headway.
This paper reports on a series of tensile pull off tests on Composite T-joints as part of a compr... more This paper reports on a series of tensile pull off tests on Composite T-joints as part of a comprehensive test programme undertaken under the auspices of the EUCLID RTP3.21 project on “Survivability, Durability and Performance of Naval Composite Structures”. The tests have been developed to evaluate joints suitable for use with large composite superstructures i.e. a hangar on a frigate type warship. To assess the performance of these joints under quasi-static and dynamic loading, test procedures have been developed using both shock table facilities and conventional servo-hydraulic test machines. The test procedures are fully complementary to ensure that test results can be directly compared. Test results established that the joint failed within the interface between the base sandwich laminate and the joint overlaminate. As joint assembly is a secondary process this is to be anticipated. Both the dynamic and quasi-static test results showed similar tensile loading performances; for quasi-static testing core shear failure immediately preceded joint failure, whereas no core failure was noted for the dynamic tests. These results suggest that the joint and base sandwich laminate chosen for the EUCLID RTP3.21 project are well matched
The paper describes experimental and numerical techniques to study the structural design and beha... more The paper describes experimental and numerical techniques to study the structural design and behaviour of thick-adherend DLS joints that are based on steel /steel and steel/composites and epoxy adhesives, with focus on long overlap joints. A standard fabrication method was followed to produce 60 specimens of various dimensions and materials.
Oil and gas exploration and exploitation in deep and ultra-deep waters challenges classical riser... more Oil and gas exploration and exploitation in deep and ultra-deep waters challenges classical riser technology and configuration. New technologies, including carbon fiber as composite armors, influence weight and strength of the riser. This can allow for more simple configurations compared with conventional ones, simplifies installation procedures and eventually lead to reduced costs. The new fiber reinforced cross section sheaths requires new analytical models in the local stress analysis tools. The current paper explores efficient and accurate implementations of orthotropic laminate sheaths into classical cross section simulation tools. The model is based on a classic partition of the analysis scheme into a combined load and response model consisting of an axisymmetric and pure bending part. The suggested model is based on full 3D elasticity solution that allows for thick cylindrical laminates taking into account all stress and strain components. The model is compared with 3D Abaqus results for a number of different lay-ups and the results show excellent agreement with the more advanced 3D simulations in both axisymmetric and bending response modes. The laminate, a thermoplastic composite layer with carbon fibers, is used as a component in an unbonded flexible pipe. The cross-sectional analysis is thus performed in the classical way.
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Papers by Dag McGeorge