Cyclic high temperature corrosion behaviour of P91/P22 dissimilar super-heater pipe joints of 70 MW CFBC boilers under Na₂SO₄ + V₂O₅ salt deposit exposure

Abstract

Thermal super-heater tubes in thermal power stations (TPS) are subjected to extreme adverse conditions that can lead to hot corrosion. Thermal super-heater tubes in thermal power plants are exposed to severe high-temperature oxidation and hot-corrosion conditions that can lead to material degradation. The alloys SA335 P91 and SA218 P22 are used in the super-heater tubes due to their exceptional strength and resistance to oxidation and corrosion at elevated temperatures. These properties are largely attributed to the alloy’s composition, which includes elements like molybdenum and chromium. The candidate materials of SA335 P91 and SA218 P22 have been welded using the PCGTAW technique, and E70S2 filler material was employed. In this study, cyclic hot-corrosion behaviour of the dissimilar joints was evaluated under Na₂SO₄ + 60 wt% V₂O₅ salt-deposit exposure at 770 °C in a laboratory-air furnace. The microstructural changes and the corrosion products of the dissimilar joints were analyzed using SEM/EDS and XRD techniques. The investigated regions exhibited different net mass-change behaviour under the applied salt-deposit exposure, with the P91 HAZ specimen showing the lowest measured mass gain and the P22 specimen showing the highest. Because one specimen was tested for each region, these results are considered specimen-specific observations rather than statistically validated differences in corrosion resistance. The passive film formation and the alloy structure were the main factors that affected the HTC and oxidation behaviour of the dissimilar joints. This research provides insights into the cyclic hot-corrosion behaviour of dissimilar P91/P22 welded joints under high temperature exposed to Na₂SO₄ + V₂O₅. The results provide a comparative assessment of the cyclic hot-corrosion behaviour of the P91/P22 dissimilar joint fabricated using E70S2 filler under the investigated laboratory conditions.

The authors' abstract, as published at the source. Next Materials, 2026 · DOI ↗