A review of nondestructive examination methods for new-building ships undergoing classification society survey

Classification societies require ship manufacturers to perform nondestructive examination (NDE) of ship weldments to ensure the welding quality of new-building ships. Ships can contain hundreds of kilometers of weld lines and 100% inspection of all welded connections is not feasible. Hence, a limited number of weldments are specified by rules of classification societies to be inspected on a sampling basis. There is a variation between the rules and guidelines used by different classification societies in terms of both philosophy and implementation which results in significant discrepancy in the prescribed checkpoints, numbers, and their locations. In this article, relevant sections of the rules of mainstream International Association of Classification Societies members are studied and potential ways of improving them are discussed. The authors have endeavored to make this study as comprehensive as much as possible. However, given the challenges of covering every single aspect and variable related to NDE in the classification societies’ rules and guidelines reviewed here, the authors can only attempt to cover the key features

Appraisal Of Mass Production Costs For Wave Energy Devices

The objective of this report is to express opinions on the order of possible costs obtainable by adopting a mass production approach to the construction of wave energy devices. From our investigations we believe the following points need to be emphasised. it is important to understand how a "cost" is derived and the relationship of the various elements within the total the designs will have to reconcile the best shape for energy absorption with less efficient but cheaper designs for production ultimately the structural cost of a device is the product of two elements: the mass in tonnes the manufacturing cost in £ per tonne The design development must aim to optimise this product to achieve the minimum cost. the eventual choice of the best device and material will need to consider all the factors in total cost. From the manufacturing point of view the key ratio which needs to be monitored is of course the cost/kw. For a device in a particular material this ratio is derived from the mass/output (tonnes/kw) and the cost/tonne (£/tonne) strategic planning will be required of both the manufacturing methods and facilities to suit the device design, again with particular attention to cost minimisation risk assessment should be included to see the effect of variances with the aim of reducing possible excesses cost reduction studies will be required during the detail design development stage and will be most successful if 'value analysis' type methods are used and emphasis placed on an iterative approach attacking the cost of all elements until a minimum figure is reached. As an example, prestressing materials make up half the material cost of the concrete Raft and are therefore a suitable target for cost reduction. This comment is relevant to all sections of the wave energy programme since the goal must be to find the minimum cost of power generation. When design and manufacturing methods can be reconciled, then significant savings in mass production costs in steel are possible. The concrete designs appear to have a reduced potential because of their size and jointing problems. We suggest that attention to manufacturing and launch out cost should be an ongoing activity once the conceptual design has been resolved. This should clarify design development programmes and by imposing disciplines prevent abort i ve development of non-productive ideas

Weld defect frequency, size statistics and probabilistic models for ship structures

Ships undergo cyclic loading which combined with weld defects can cause fatigue failure. Remaining fatigue life of structures containing defects can be estimated using the defect size. The defect data for ships is non-existent in literature or belong to old offshore structures. In this research, the data collected from two ships are presented. The statistical analysis of the data shows that the Hybrid Laser Welding has lower defect rates than other common arc welding processes indicating that less quality control inspection may be allowed. The defect length values from the studied ships were smaller than those from offshore structures

Friction stir welding of thin section aluminium extrusions for marine applications

This dissertation focuses on the development of a welding extrusion feeder, tool and schedule for implementation of defect-free butt welds on long, thin and complex-shape aluminium extrusions, as used by the marine industry. Viability of employing Friction Stir Welding (FSW) as a welding technology for joining long extrusions with a short-bed and bolt-on feeder to facilitate onsite fabrication of flat structures in shipbuilding is evaluated. An FSW feeder, tool and process control unit were designed, developed and integrated with an existing FSW platform, to facilitate implementation of continuous welds. Weld data acquired from literature review, experimentation, mechanical testing and metallographic analysis was used in design considerations for the development of a feeder. Subsequently, butt welds were implemented successfully on long 3 mm AA6082-T6 extrusions, during continuous FSW on the feeder. A specially adapted tool, the Floating Bobbin Tool, used with the feeder to implement butt welds was designed and developed from literature tool heuristics and weld trials. The tool eliminated the need for a backing bar and enabled tool-workpiece auto-alignment, beneficial with thin-section extrusions. Effect of rotational and weld speed and tool geometry of two tools (Tool 1 and 2), on weld forces and quality was tested, to establish optimum parameters for attaining high quality welds. Tool geometry had a profound effect on weld forces and integrity; Tool 2 welds exhibited superior and consistent weld quality, meeting maritime rules and standards and proving the adequacy of using FSW for joining long thin extrusions. Feeder process control, automation and optimisation, was implemented by process control unit devices, in addition to force and position control provided by the existing FSW platform. Owing to process control, automation and optimisation during continuous FSW of thin long and complex-shape aluminium extrusions, welding setup times and process variations are minimised and chances for defect-free welds increased, boosting production and cost savings in large panel fabrication in shipbuilding

Friction stir welding of thin section aluminium extrusions for marine applications

This dissertation focuses on the development of a welding extrusion feeder, tool and schedule for implementation of defect-free butt welds on long, thin and complex-shape aluminium extrusions, as used by the marine industry. Viability of employing Friction Stir Welding (FSW) as a welding technology for joining long extrusions with a short-bed and bolt-on feeder to facilitate onsite fabrication of flat structures in shipbuilding is evaluated. An FSW feeder, tool and process control unit were designed, developed and integrated with an existing FSW platform, to facilitate implementation of continuous welds. Weld data acquired from literature review, experimentation, mechanical testing and metallographic analysis was used in design considerations for the development of a feeder. Subsequently, butt welds were implemented successfully on long 3 mm AA6082-T6 extrusions, during continuous FSW on the feeder. A specially adapted tool, the Floating Bobbin Tool, used with the feeder to implement butt welds was designed and developed from literature tool heuristics and weld trials. The tool eliminated the need for a backing bar and enabled tool-workpiece auto-alignment, beneficial with thin-section extrusions. Effect of rotational and weld speed and tool geometry of two tools (Tool 1 and 2), on weld forces and quality was tested, to establish optimum parameters for attaining high quality welds. Tool geometry had a profound effect on weld forces and integrity; Tool 2 welds exhibited superior and consistent weld quality, meeting maritime rules and standards and proving the adequacy of using FSW for joining long thin extrusions. Feeder process control, automation and optimisation, was implemented by process control unit devices, in addition to force and position control provided by the existing FSW platform. Owing to process control, automation and optimisation during continuous FSW of thin long and complex-shape aluminium extrusions, welding setup times and process variations are minimised and chances for defect-free welds increased, boosting production and cost savings in large panel fabrication in shipbuilding

Feed forward control of welding process parameters through on-line ultrasonic thickness measurement

Accurate control of welding parameters, such as arc power and wire speed, is critical for successful and appropriate weld joint penetration. The thickness of components being welded is a key parameter in defining optimum arc power for successful penetration, but is not always known beforehand or well controlled in manual and automated welding operations. This paper presents a novel feed-forward, sensor enabled, arc process control strategy based on ultrasonic thickness measurement. An ultrasonic wheel probe, deployed simultaneously alongside the welding torch, enables plate thickness measurement when coupled with a low-latency thickness measurement algorithm deployed on a real-time controller. An automated GTAW fusion control strategy, based on wheel probe measured plate thickness, provides direct input control of arc current, welding torch travel speed and filler wire feed rate. A parametric relationship between ultrasonically measured sample thickness and key arc welding parameters for welding S275 mild steel samples of thickness between 4.1 mm and 6.1 mm was established and verified. It is demonstrated that the system can measure and derive plate thickness while adapting arc power in real-time, with sufficiently low-latency, to allow consistent weld seam and uniform penetration on variable thickness steel samples, which under normal open-loop circumstances lead to sample burn-through and excessive penetration

Shipbuilding and Ship Repair Workers around the World

Maritime trade is the backbone of the world’s economy. Around ninety percent of all goods are transported by ship, and since World War II, shipbuilding has undergone major changes in response to new commercial pressures and opportunities. Early British dominance, for example, was later undermined in the 1950s by competition from the Japanese, who have since been overtaken by South Korea and, most recently, China. The case studies in this volume trace these and other important developments in the shipbuilding and ship repair industries, as well as workers’ responses to these historic transformations

Optimising non-destructive examination of newbuilding ship hull structures by developing a data-centric risk and reliability framework based on fracture mechanics

This thesis was previously held under moratorium from 18/11/19 to 18/11/21Ship structures are made of steel members that are joined with welds. Welded connections may contain various imperfections. These imperfections are inherent to this joining technology. Design rules and standards are based on the assumption that welds are made to good a workmanship level. Hence, a ship is inspected during construction to make sure it is reasonably defect-free. However, since 100% inspection coverage is not feasible, only partial inspection has been required by classification societies. Classification societies have developed rules, standards, and guidelines specifying the extent to which inspection should be performed. In this research, a review of rules and standards from classification bodies showed some limitations in current practices. One key limitation is that the rules favour a “one-size-fits-all” approach. In addition to that, a significant discrepancy exists between rules of different classification societies. In this thesis, an innovative framework is proposed, which combines a risk and reliability approach with a statistical sampling scheme achieving targeted and cost-effective inspections. The developed reliability model predicts the failure probability of the structure based on probabilistic fracture mechanics. Various uncertain variables influencing the predictive reliability model are identified, and their effects are considered. The data for two key variables, namely, defect statistics and material toughness are gathered and analysed using appropriate statistical analysis methods. A reliability code is developed based Convolution Integral (CI), which estimates the predictive reliability using the analysed data. Statistical sampling principles are then used to specify the number required NDT checkpoints to achieve a certain statistical confidence about the reliability of structure and the limits set by statistical process control (SPC). The framework allows for updating the predictive reliability estimation of the structure using the inspection findings by employing a Bayesian updating method. The applicability of the framework is clearly demonstrated in a case study structure.Ship structures are made of steel members that are joined with welds. Welded connections may contain various imperfections. These imperfections are inherent to this joining technology. Design rules and standards are based on the assumption that welds are made to good a workmanship level. Hence, a ship is inspected during construction to make sure it is reasonably defect-free. However, since 100% inspection coverage is not feasible, only partial inspection has been required by classification societies. Classification societies have developed rules, standards, and guidelines specifying the extent to which inspection should be performed. In this research, a review of rules and standards from classification bodies showed some limitations in current practices. One key limitation is that the rules favour a “one-size-fits-all” approach. In addition to that, a significant discrepancy exists between rules of different classification societies. In this thesis, an innovative framework is proposed, which combines a risk and reliability approach with a statistical sampling scheme achieving targeted and cost-effective inspections. The developed reliability model predicts the failure probability of the structure based on probabilistic fracture mechanics. Various uncertain variables influencing the predictive reliability model are identified, and their effects are considered. The data for two key variables, namely, defect statistics and material toughness are gathered and analysed using appropriate statistical analysis methods. A reliability code is developed based Convolution Integral (CI), which estimates the predictive reliability using the analysed data. Statistical sampling principles are then used to specify the number required NDT checkpoints to achieve a certain statistical confidence about the reliability of structure and the limits set by statistical process control (SPC). The framework allows for updating the predictive reliability estimation of the structure using the inspection findings by employing a Bayesian updating method. The applicability of the framework is clearly demonstrated in a case study structure