In September 2017, during a five-year special inspection of the WHPC jacket, 9 cracks were found, including 5 suspected weld defects less than 5mm deep that needed to be sanded.
Subsequently, an independent third-party investigation was conducted by DNVGL classification society in 2018, followed by preliminary comparative study of repair scheme for two large deep cracks N220 and N214 nodes from weld defects and an in-depth expert review evaluation for two proposed repair schemes – dry cabin method or unstressed grout clamp scheme towards end of 2019.
Finally, the latter scheme based on grout-clamp repair was selected.
An onshore grouting trial on reduced scale 2:1 was carried out successfully in early 2022 as proof-of-concept to showcase infill ability and strength development of ultra-high performance cementitious (UHPC) grout NaX® Q140-E, which is manufactured by Nautec.
This was then followed by actual site installation and grouting work implementation in late-2022.
- Supply of NaX® UHPC grout
- Technical Consultancy
Scope of Work
- Supply of grouting materials and technical consultancy on grouting implementation.
- The complex geometry of the structure to be repaired and strengthened entailed up to six different parts of steel clamps to be infilled 100% in one single grouting operation.
- Multiple grouting inlets had to be installed at strategic locations to ensure proper infilling of clamps.
- Onshore grouting trial on mock-up scale reduction 2:1 for proof-of-concept on proposed grouting inlet locations and subsequent post-trial inspection to confirm 100% in-filled clamp.
- The close collaboration between the client and Nautec and the technical support provided by Nautec resulted in successful implementation of the grouting solution.
- Early strength development of NaX® Q140-E is superior with 1-day strength 10 times higher than the market average for cold temperatures.
- The fatigue performance of NaX® Q140-E has been verified through a thorough test campaign with Leibnizt Universität, Hannover confirming that DNV-OS-C502 can be used conservatively for the fatigue life prediction of grouted connections using NaX® Q140-E.
Click here to download the project case history.