Sif is introducing an innovative welding technique to make welded joints strong and welded connections durable: The Cold Wire Tandem-Twin Narrow Gap SAW (CWTT-NGSAW) process. The technique has already been used temporarily before but there was no need for further development until the arrival of the XXXL monopiles. The technique will also be implemented in the new Maasvlakte plant.
The latest XXXL monopiles weigh between 1,600 and 2,000 tonnes. At sea, these giant structures have to withstand extreme conditions such as current, wave action and salt water. These factors make a strong and durable welded joint essential, especially for the circumferential welds that experience the most stress.
Efficient welding
Speeding up the welding process without compromising the strength and quality of the welded connection is a challenge. The XXXL monopiles, which can be up to 100 metres long and have a circumference of 35 metres, require numerous weld connections with significant weld lengths and thicknesses. There are several ways to make the monopile welding process more efficient; including increasing the deposition rate, reducing the welding volume and/or increasing the duty cycle, Sif says.
The Cold Wire Tandem-Twin Narrow Gap SAW (CWTT-NGSAW) process
The new welding technique has been developed in-house, by Sif’s Process Technology and Innovation (PT&I) department. The NGSAW (Narrow Gap Submerged Arc Welding) welding process is not in itself a new technique. It has been used for decades in various industries, such as welding thick-walled reactors or pressure vessels. Traditionally, this often involves only one welding head and a maximum of two welding wires, and the Narrow-Gap technique is rarely used for series production, such as in the production of monopiles.
Sif’s new approach is said to change this. The company now welds simultaneously with multiple welding heads in a Narrow-Gap pre-processing operation. This means that one operator operates a welding machine equipped with multiple welding heads, each with five welding wires. This setup makes the welding process extremely efficient.
Although this technique has been used temporarily before, between 2016 and 2018, at that time it was not fully reliable and ready for mass production. 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.
Benefits of the new welding technology
Reduced welding volume: by reducing the welding volume, the amount of welding consumables required, energy consumption and welding time are being reduced. The fatigue strength of the weld increases, allowing designers to reduce material thickness and thus save costs.
Higher deposition rate: a non-current-carrying “cold wire” is added to the weld pool, achieving a higher deposition rate without additional energy consumption. This reduces welding time and preserves weld quality.
Implementation of the new technique at Sif
The transition to this new welding method also brings challenges, Sif says, such as the optimisation of welding parameters and process control. To meet these challenges, Sif have developed a welding head and a welding process adapted to it, which provide an operation (at least) as robust as we had before this transition.
Sif mentions that their welders have now been trained, and have successfully applied the welding technique in Roermond, with very low reject rates. The company is currently also having a large number of welding heads built for their new manufacturing halls on our Maasvlakte plant. Source: Sif
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