New solutions in a professional chain. Our profession is very much in development. Both the demand for wind turbines and their scope are increasing with every year that passes, and that has an impact that sends ripples through the chain. It all starts with strong foundations that require as little maintenance as possible and weigh as little as possible.

John Goessens and his engineering team at Sif work with a range of partners on the innovation of manufacturability and the production process for new designs and foundations. ‘We are on the cusp of new developments and that gives us a glimpse into the future,' says John. 'It’s fantastic to be able to work on something that is bigger than yourself.’

Experienced pioneers

Sif is the largest supplier of offshore foundations for wind projects (OWF) in Europe, alongside Ørsted and Siemens Gamesa. In 2001, Sif produced the first OWF, but we have been building experience in tubulars for oil and gas platforms since 1948. ‘This knowledge and experience gives a real edge,’ explains John, ‘but we don’t keep it to ourselves; we work as partners. To us, an efficient, high-quality, and environmentally-friendly chain is just as important as our own ambitions.’

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Big, bigger, biggest

In 2001, we created the first foundations with a four-metre diameter – today eight metres is very common. It’s not just the size that’s on the increase – the demand, series capability, and need for efficiency in the production process are all growing. ‘We’re continually adapting our hoisting equipment, drilling templates, and machinery to the changing requirements,' says John. 'Our newest machinery has even been designed to cope with an increase up to eleven metres.’ With every year that has passed, it has become more and more obvious that the plant in Roermond would be too small for this level of growth, and the Maasvlakte in Rotterdam emerged as the ideal location for a second assembly and coating facility. With the long, deep-sea wharf, installation vessels can dock even closer, which saves a considerable amount of installation time and money.

Slip joint: testing and measuring

After installation, maintenance of the foundations is extremely labour-intensive and costly. With the monopile that we’re using, the high maintenance factor is largely due to the use of bolts in the joint between the upper section (the transition piece) and the lower section (the monopile). The old concrete grout joint would experience movement over time, and that was a problem. Two pilots – ‘slip joint’ and ‘double slip joint’ – are currently researching and testing new solutions. ‘As an example, we’re researching a joint that comprises two conical parts that slide into one another and clamp together through their own weight, rendering bolts and concrete unnecessary,' adds John. 'Another advantage is that the transition piece and monopile joint can be under water since we no longer need to carry out any maintenance on the joint. This opens up the possibility of making the monopile shorter and lighter, which brings even more benefits when it comes to logistics and installation. Sif is taking an active role in this research by providing input on fabrication options and the construction of prototypes, both scale models and full scale.’

Rough yet precise

‘With the slip joint, the challenge that we face is the precision of the rolling, and with the enormous diameters, things are very tight,' says John. 'We’re looking at how the calculations can be fully optimized and what this will mean for overall affordability.’ John has been working at Sif for 23 years and enjoys being as close to the product as possible. ‘In engineering, we work with enormous steel tubulars every day and that still has an air of excitement about it – on the diagrams and when you’re standing between them, when they’re being welded together and when they’re erected out at sea. Yes, I’m extremely proud that I can play a part in all of this!’