A test waterwall was fabricated so that alternatives to alloy 625 could be exposed in the first pass of the waste incineration plant Haderslev. The chemical environment from the waste incineration was also monitored by analyzing deposits and corrosion products from various locations in the boiler. 

In this paper, a detailed analysis was performed to define the variance between both Nickel alloys 825 and 625 Multi-alloys. A comprehensive experiment and testing was done to evaluate both mechanical and chemical properties for the flanges with weld overlay, fittings and pipe components. The results of the study indicated several challenges and the gaps between both materials. Therefore, an initiative was led to promote the current process in order to prevent reoccurrence and mitigate associated consequences of failure by investigating and defining the root cause analysis. In order to ensure bridging the gaps, the paper concludes with a list of recommendations for the actions taken towards the material and vendor quality in order to proceed forward with the corrective actions and precautions for utilization whenever different PMI readings are found in cladding to continue supplying high quality products as expected.

Weld overlay has been successfully used to mitigate high temperature corrosion issues in coal-fired boilers since the1990s, such as in waterwall and superheater/reheater area. Weld overlay is typically applied in shop or field by using Gas Metal Arc Welding (GMAW) process for boiler waterwall application, and the overlay welding is performed in vertical down welding mode (3G welding position) in subcritical and supercritical boiler waterwall applications. With the rapid development of coal-fired boiler market in China, ultra-supercritical boilers are becoming the dominated boiler type which often has spiral waterwall design. Most of ultra-supercritical coal-fired boiler waterwall consists of CrMo steel tubes, which could suffer severe high temperature corrosion attack after the installation of low NOx burners. It is expected that weld overlay could provide a long-term high temperature corrosion protection for ultra-supercritical boiler waterwall based on previous weld overlay study and application experience. However, for the spiral waterwall with inclined tube design, its field overlay welding is highly challenging and significantly different from typical vertical boiler waterwall overlay welding. The challenge and difference include welding position, welding sequence, welding parameters, and overlay properties, etc. This paper presents a successful field application of 309L stainless steel and 622 Ni-based alloy weld overlay on the spiral waterwall of an ultra-supercritical coal-fired boiler, including the welding development, simulation, and experience of overlay welding on the inclined tubes, along with the characterization of the weld overlay applied.