A collaboration between Cambridge Vacuum Engineering, SSE Renewables, Sif Group, and The Welding Institute (TWI) used electron beam welding for a monopile destined for Dogger Bank, 130km off the northeast coast of England.
Monopiles are currently fabricated using conventional techniques such as submerged arc welding but the consortium has demonstrated that electron beam welding is quicker, cheaper, cleaner, more energy efficient while still producing high quality welds with excellent fatigue properties, the partners say.
The type of electron beam welding technology used – called Ebflow – is a new development within the electron beam welding industry. Instead of welding inside a costly and size-limiting vacuum chamber, Ebflow uses a local vacuum system that creates and maintains a vacuum around only the seam that is being welded. This technique makes it feasible to use electron beam welding on large structures, such as the biggest monopiles, reducing costs and improving productivity.
The technology – developed by Cambridge Vacuum Engineering (CVE) – has been shown to weld monopiles at least 25 times faster than current methods, while using 90% less energy, costing 88% less, and producing 97% less CO2 emissions than submerged arc welding (SAW) methods.
The project required installation of an Ebflow system at Sif’s Maasvlakte 2 facility in Rotterdam to perform several longitudinal welds on 2750 mm length seams on eight-metre diameter rolled cans with a wall thickness of between 67 and 85 mm.
Qualification of the welding machine, weld procedures and operators was witnessed by third party inspectors and the regulatory body DNV, which subsequently issued a technology qualification for electron beam welding and non-destructive testing (NDT) of the longitudinal seams produced with the process. Testing showed that Ebflow produces welds with fatigue strength that is at least as good, if not better, than equivalent arc welded joints.
The resulting can was incorporated into a monopile transition piece in January 2023 and is scheduled to be installed offshore as part of a foundation in Dogger Bank Wind Farm in late 2023.
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Olly Cass, SSE Renewables project director for Dogger Bank wind farm, said: “With monopile type foundations accounting for over 90% of foundations used in UK projects, Ebflow RPEB [reduced pressure, electron beam] could realise significant cost savings on future projects.
“These substantial savings will not only benefit the UK offshore engineering industry but could be passed on to UK energy consumers.
“We’re proud to be pioneering this innovative technique on Dogger Bank Wind Farm by demonstrating its capabilities on a critical offshore component and this would not have been possible without the great collaborative work with Cambridge Vacuum Engineering (CVE), Sif Group, and TWI. We’re excited about what could be achieved by scaling up this method to pick up the pace as we work towards net zero targets.”
Dogger Bank Wind Farm is a joint venture between SSE Renewables, Equinor and Vårgrønn. The farm is being built in three 1.2GW phases and is expected to start generating power this summer.
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