Carburization Resistance of High-Cr, High-Ni Weld Overlayed Furnace Tubes for Ethylene Pyrolysis

摘要

The carburization behavior of furnace tubes with high-Cr, high-Ni alloy weld overlay has been evaluated. A thick layer of 45 % Cr, 50 % Ni, 1 % Mo alloy was welded on the inner surface of conventional HP-mod, type cast tubes using the Plasma Powder Welding (PPW) technique. The evaluation was conducted both in laboratory under accelerated conditions and in the field tests. The results show that if the PPW layer was applied, no carburization was observed in the base material under the conditions after 4 years operation where severe carburization occurred in conventional tubes already after 1 year. Using the Larson-Miller parameter and the equilibrium phase diagrams of the PPW and HP-mod, alloy compositions, the carburization tube life are predicted to be more than three times longer than that of conventional tubes. This significant tube life improvement can be explained by the very slow carburization of the PPW layer due to the presence of a continuous chromium oxide surface layer which is a barrier for carbon diffusion from the surface into the PPW layer in combination with the effect of the PPW / base material interface which is a barrier to carbon diffusion into the base material. The continuous, self healing and anti-catalytic chromium oxide surface layer is also expected to suppress the catalytic coke formation which results in longer run length.