voestalpine Böhler Welding provides high-temperature corrosion and oxidation-resistant welding consumables for the overlay welding of boiler tubes and other components to achieve optimal operation of waste incineration plants. Overlay cladding of new or corroded parts has become the primary solution to combat characteristic corrosion in waste incineration plants. Due to the high chloride containing atmosphere, nickel-base filler materials need to be used.
Alloy 625 has excellent heat and corrosion resistance and is commonly used in steam generation with a service temperature up to 450°C. It is frequently applied in the cladding of membrane walls, evaporators and preheaters.
Alloy 686 has a very high pitting resistance equivalent number PREN and, thanks to a higher nickel and molybdenum content, it has an higher resistance to corrosion in reducing environment, making it suitable for the cladding of heater pipes with temperatures above 450°C.
For the corrosion and oxidation resistance of the weld overlay, not only the chemistry of the welding consumable used is decisive. The welding process and the welding parameters have a direct influence on the overlay chemistry. To optimize this resistance, a low Fe content is aimed for, which is why low heat input techniques are used. By optimizing the GMAW pulse process, Böhler Welding has developed the clad pulse process to reduce the dilution with the base material during welding and thus lower the Fe content of the overlay.
For new components, welding overlays are applied to membrane walls in workshops using special stationary equipment.
For corroded components, mobile welding units can be used on site in the combustion chamber to renew and repair the corrosion protection layers. Various welding techniques can be used, the most common one being the pulse GMAW process, but other techniques such as thermal spraying can also be used. Arc spraying, using solid or cored wires with specific chemistry, is a good alternative to the pulse GMAW.
When accessibility to the automated equipment is limited, manual SMAW or GTAW is used in cladding processes.
Weld overlays are applied on single tubes in workshops with stationary equipment. The preferred welding process is GMAW pulse welding. To avoid tube distortion, running cold water is injected into the tubes in order to cool them down during the welding process.
Special wear plates, designed to withstand abrasion at high temperatures, are used to protect the chute from the abrasion of waste when feeding the combustion chamber.
