Combining ultrasound non-destructive testing and bolting methods to improve reliability on bolted flange connections in offshore wind
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This paper introduces the research undertaken to improve the reliability of bolted flange connections in structural engineering, with offshore wind turbines being used as an example. The current problem is that bolts are often over-or under-loaded, leading to premature failure. This shows that the existing loading methods cannot be relied on to balance the strains, which is the root cause of the bolting problem. This work highlights the importance of good asset management of bolted flange connections in the safety aspects of bolted flange connections.
Combining ultrasound non-destructive testing and bolting methods to improve reliability on bolted flange connections in offshore wind
- 1. Combining ultrasound non-destructive testing and bolting methods to improve reliability on bolted flange connections in offshore wind 56th Annual British Conference on Non-Destructive Testing, UK 5 September 2017 Dominik Kujawski, Dr Shaun West and Henk van den Berg
- 2. 56th Annual British Conference on Non-Destructive Testing, UK | June 2016 |Kujawski, West & van den Berg Introduction The problem and the purpose of this paper To highlight the importance of bolts monitoring in critical flanges This paper introduces the research undertaken to improve the reliability of bolted flange connections in structural engineering on the example of offshore wind Research to improve the reliability of bolted flange connections Purpose of this paper Bolts are often over- or under-loaded and can lead to early failure Problem
- 3. 56th Annual British Conference on Non-Destructive Testing, UK | June 2016 |Kujawski, West & van den Berg Problem statement Current practise in the industry potential problems What does the literature tell us? - Offshore is exposed to high dynamic loads - Inaccurate selections of bolting resistance - Bolt cross torque results in loss of accuracy - Loss of transparency in the applied preload https://www.nrdc.org/stories/wind-farm-great-lakes-lets-give-it-twirl The root cause of bolting problem is the imbalance of strains
- 4. 56th Annual British Conference on Non-Destructive Testing, UK | June 2016 |Kujawski, West & van den Berg Introduction Why bolting is important? https://www.youtube.com/watch?v=A-FJI-U2chA Key facts - This is a critical aspect of the asset integrity - Connected surfaces can withstand huge pressure - For reliability bolts must be loaded correctly The ability to transfer load from one component to another requires safe and efficient designs
- 5. 56th Annual British Conference on Non-Destructive Testing, UK | June 2016 |Kujawski, West & van den Berg Background Why ultrasound monitoring is valuable? What does the literature tell us? - Advantage of ultrasound testing is accuracy - The bolt it stretches like a spring with applied load - Applied load is measured by the stretch amount The bolt elongation difficult to measure - ultrasound monitoring is considered as valuable
- 6. 56th Annual British Conference on Non-Destructive Testing, UK | June 2016 |Kujawski, West & van den Berg Background Current practise in the industry traditional torque sequence What does the literature tell us? - Done in three stages using a quadrant protocol - Intrinsic errors friction consumes 90% of the torque - The errors of 50% is common The sequence with the traditional torque technique increases the torque after completing every stage
- 7. 56th Annual British Conference on Non-Destructive Testing, UK | June 2016 |Kujawski, West & van den Berg Methodology A four step methodology was applied in this study Traditional torque Lab case 1 Target load 400kN Torque wrench Ultrasound NDT New method Lab case 2 Target load 400kN Combined methods Ultrasound NDT Statistical analyses Spread Distribution Cumulative percentage Box plot analysis Compare lab results with real project data Compare both cases in a table
- 8. 56th Annual British Conference on Non-Destructive Testing, UK | June 2016 |Kujawski, West & van den Berg Results and analysis Flange chart comparison of the both lab cases The crosstalk variations are one of the main reasons for the premature failure in the bolted connections Traditional torque lab case 1 New method lab case 2
- 9. 56th Annual British Conference on Non-Destructive Testing, UK | June 2016 |Kujawski, West & van den Berg Results and analysis Spread chart comparison of the load target deviations for both lab cases Traditional torque lab case 1 New method lab case 2 The targeted number of measurement results are 6% for lab case 1 and 28% for lab case 2
- 10. 56th Annual British Conference on Non-Destructive Testing, UK | June 2016 |Kujawski, West & van den Berg Results and analysis Distribution and cumulative percentage charts comparison for both lab cases Traditional torque lab case 1 New method lab case 2 Lab case 2 has a higher number of measurements closer to the targeted value of 400kN
- 11. 56th Annual British Conference on Non-Destructive Testing, UK | June 2016 |Kujawski, West & van den Berg Results and analysis Percentage deviation comparison of both lab cases Key findings - The percentage deviation for lab case 1 is from 20% above and more than 30% below - The percentage deviation for lab case 2 is less than 10% above and below Box plot chart provides a richer understanding of both lab cases and new method project application
- 12. 56th Annual British Conference on Non-Destructive Testing, UK | June 2016 |Kujawski, West & van den Berg Results and analysis Percentage deviation comparison of both lab cases and real project measurements Key finding - The percentage deviation for the real project measurements is less than 10% both above and below Box plot chart provides a richer understanding of both lab cases and new method project application
- 13. 56th Annual British Conference on Non-Destructive Testing, UK | June 2016 |Kujawski, West & van den Berg Results and analysis Comparison of traditional and new method tightening techniques in the lab environment Traditional torque New method Strain balance 60% spread 10% spread Time to complete a test flange 4 hours 2 hours Employees needed Regular Regular Transparency - Every bolt can be tracked Long-term asset management - Ultrasound testing provides quality assurance This table provides a direct comparison between the traditional and the new method
- 14. 56th Annual British Conference on Non-Destructive Testing, UK | June 2016 |Kujawski, West & van den Berg Results and analysis The key observations from the analysis were Initial findings confirmed that the new method increases the accuracy and reliability - Increased strain balance - Two times faster - Performed by regular employees - Increased transparency The new method increases the availability and reliability, decreasing unscheduled maintenance
- 15. 56th Annual British Conference on Non-Destructive Testing, UK | June 2016 |Kujawski, West & van den Berg Closing Conclusions This study of over 10,000 project data points confirms that the new method of tightening improves asset integrity in comparison to traditional approaches Tightening is challenging due to the increasing size of constructions The traditional tightening methods do not provide balanced loading It is possible to combine NDT and bolt tightening Confirmed by statistical analyses of 10,000 project data points
- 16. 56th Annual British Conference on Non-Destructive Testing, UK | June 2016 |Kujawski, West & van den Berg Thanks for your time!