Studies on the Behavior of Ni-20Cr Plasma Spray Coatings Applied on Boiler Tube Steels in Molten Salt (Na2SO4-60%V2O5) Environment at 900°C

• Published in: Corrosion (Houston, Tex.) Tex.), 2006-06, Vol.62 (6), p.533-540
• Main Authors: Sidhu, B.S., Prakash, S.
• Format: Article
• Language: English
• Subjects: Aluminum; Applied sciences; Boiler tubes; Chemical bonds; Coatings; Corrosion; Corrosion environments; Corrosion mechanisms; Corrosion rate; Corrosion resistance; Exact sciences and technology; Hot corrosion; Ions; Metallic coatings; Metals. Metallurgy; Molten salts; Nickel chromium alloys; Production techniques; Salts; Scale (corrosion); Sodium sulfate; Spalling; Steel; Surface treatment; Vanadium pentoxide
• ISSN: 0010-9312; 1938-159X
• DOI: 10.5006/1.3279912

ABSTRACTThe corrosion of metals and alloys in oxidizing/sulfidizing atmospheres at elevated temperatures has become a matter of increasing concern.1 Metals and alloys sometimes experience accelerated oxidation when their surfaces are covered with a thin film of fused salt in an oxidizing gas atmosphere at elevated temperatures. In hot corrosion, metals and alloys are subjected to degradation at much higher rates than in gaseous oxidation, with a porous nonprotective oxide scale formed at their surface and sulfides in the substrate.2-5 Some fuel oil contains sodium, vanadium, and sulfur as impurities that form complex vanadates through a reaction in the combustion systems. These compounds deposit on the surface of the materials and induce accelerated oxidation.6-7 The maintenance costs for replacing broken pipes in some installations are very high and have been estimated to be about 54% of the total production costs.8 One possible way to attack these problems is to use thin antiwear and antioxidation coatings with good thermal conductivity, such as plasma-sprayed nickel-based or iron-based and chromium-nickelbased alloyed coatings.8-10 Thermal spray coatings are used widely to protect the alloy substrate against high-temperature corrosion and erosion.11-16 The oxidation behavior of plasma-sprayed coatings was studied by Hidalgo,8 et al., with an aim to reduce maintenance costs and down time at power generating plants. Protective coatings are being used on structural alloys in energy conversion and utilization systems to protect their surface from oxidation and erosion. Almost any material can be used for plasma spraying on almost any type of substrate. This flexibility is probably one of the major reasons for the rapid expansion of this technology. Applications for plasma spraying include corrosion, temperature, and abrasion-resistant coatings. The technique also helps