CMT CLADDING TOWER FOR FINNED WALLS

The large water-tube boilers used in commercial and industrial power generation use heating surfaces called finned walls made from tubes and flat iron. Due to the changing trends in fuels and the burning of increasingly difficult and aggressive fuels, it is necessary to develop additional anti-corrosion protection for the finned walls. Hardfacing is the most efficient way to protect the finned wall surfaces. 

“To surface the finned tubes, we use a cladding tower from Fronius Welding Automation that is approximately 15 meters high,” explains Arkadiusz Osuch, managing director of FAKOP. “It can accommodate two 12-meter-high and 1.6-meter-wide finned walls and is operated by two elevator platforms, each equipped with innovative CMT welding technology.” 

Iron in the weld metal diluted to less than 3%

Many challenges are associated with the process of overlay welding. The ratio of base material to applied alloy is crucial for the effectiveness of the corrosion protection. The aim is to keep the ratio as low as possible while ensuring good fusion between the base material and the protective layer. A lower base material content ratio means longer equipment service life. 

Jaroslaw Olej, senior welding expert, confirms that “The mixing ratio is now regularly below 3%.” 

Before the management of FAKOP decided to purchase a mechanical CMT welding system, the finned walls were surfaced using other techniques. 

In order to satisfy the high quality demands of their customers, FAKOP's welding technology production engineers pay attention to every detail during the pretreatment of finned walls. Once the surface pretreatment is complete, the finned walls move on to overlay welding, which takes place in dust- and rust-free conditions.

The welding process is crucial

When opting for the Fronius welding tower, a key factor was the use of CMT technology. Its advantage lies in the digital process control, which independently detects short circuits and supports droplet detachment by retracting the welding wire. This creates a back-and-forth motion that keeps the arc phase short and reduces heat input. The result is a material transfer that enables spatter-free cladding results with a particularly smooth surface, soft seam overlaps, and a consistent layer thickness.

“Nowadays, we find the majority of our customers require the CMT process,” says Olej, adding “You can safely say it’s established itself as the standard, and those who know how to use it properly enjoy good opportunities in the market.” 

Expertise comes up trumps

Welding expertise and experience are vital. For example, arc stability and the susceptibility to porosity largely depend on an equally optimal and constant wire speed. 

“From the inner liner to the welding torch, we are dealing with an enormous wire length of around 15 meters. That’s why it’s difficult to keep the speed completely stable - you need a reliable wirefeeder, a series of tests, and sufficient expertise,” says Piotr Ogórek, technology and development expert, explaining the importance of specialist knowledge in laying membrane walls. “A further criterion is the ideal position of the welding torch, because spatter will occur if the torch angle is set incorrectly,” Ogórek adds.

The stick-out and associated arc length are other significant quality-determining factors which–together with constant wire speed–contribute to reducing porosity. With the help of Fronius, the specialists at FAKOP adapted the properties of their TPS/i CMT power sources to achieve optimum application results without pore formation by adjusting the stick-out accordingly.