A photo showing an extra large monopile lying at Sif's production site with Sif worker in front

Sif to Employ New Welding Method in Production of XXXL Monopiles

Dutch offshore wind foundation manufacturer, Sif, will be using a new welding technique in the production process of XXXL monopiles in its new production halls on the Maasvlakte, Rotterdam. The Cold Wire Tandem-Twin Narrow Gap SAW (CWTT-NGSAW) process is said to make welded joints stronger and welded connections more durable.

The method was developed by Sif’s Process Technology and Innovation (PT&I) department and has already been tried out at the company’s facility in Roermond. While the technique in itself is not new, it is rarely used in serial production such as in the manufacturing of offshore wind monopiles.

“Our welders have now been trained, and we have successfully applied the welding technique in Roermond, with very low reject rates. We owe this success to the joint effort of various departments within Sif and the commitment of our expert operators,” the company said in a social media post.

Monopiles that are being rolled out now are carrying 12-16 MW wind turbines and have diameters of up to 11 metres, and the latest XXXL monopiles weigh between 1,600 and 2,000 tonnes. With the addition of being installed far offshore, strong and durable welded joints are essential, especially for the circumferential welds that experience the most stress, Sif explained in an article posted on 10 July.

“A flawless weld is crucial to the design, construction and lifetime of these foundations, which must last at least 25 years,” the company said.

The NGSAW welding process traditionally often involves only one welding head and a maximum of two welding wires. For the serial production of XXXL monopiles, Sif will be welding simultaneously with multiple welding heads in a Narrow-Gap pre-processing operation using a welding machine with multiple welding heads, each with five welding wires.

According to the Dutch company, it had already used the method earlier, between 2016 and 2018, but it was not fully reliable and ready for mass production at the time.

“Because there was no urgent need to develop the technique further. With the arrival of the XXXL monopiles that need is now here, and we have further perfected the technique,” Sif said.

The company is currently building an extension to the monopile production facility at its Maasvlakte 2 site in Rotterdam. The first production line is expected to go into operation this month (July 2024).

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Following the first production going live this Summer, Sif expects the new manufacturing facilities to be in full operation in the first half of 2025.


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