PurposeFour thermal spray coatings were subjected to high temperature corrosive environments of oil‐fired boiler conditions to compare their corrosion protection under simulated conditions. The coatings included FeCrAl, Tafaloy 45CT, which were arc‐sprayed, 50Ni‐50Cr and Cr3C2‐NiCr, which were coated by high velocity oxy fuel spray (HVOF) method.Design/methodology/approachThe coating substrates used were SA213TP 347H, SA213 T11 and SA213 T22 alloys that are widely used as boiler tube materials. Specimens were covered with a synthetic ash mixture of 70 per cent V2O5‐20 per cent Na2SO4‐10 per cent NaCl and exposed to 550°C and 650oC°for 192 h (6 cycles). After high temperature corrosion tests, weight change curves were obtained; specimens were examined by metallographical techniques, scanning electron microscopy and EDX analyses.FindingsSalt deposits attacked steels and coatings during the exposure. The corrosion rates were strongly affected by the composition of the scale formed adjacent to the steels and coatings surfaces. Austenitic steel was only bare material that experienced uniform corrosion in the tests. Ferritic steels were primarily attacked by grain boundary corrosion. Thermally sprayed coatings were mainly attached through oxides and voids at splat boundaries. FeCrAl and 50Ni‐50Cr were prone to spalling. Tafaloy 45CT is also a promising method for producing homogenous coatings. Cr3C2‐NiCr 80/20 coating remained mostly intact.Originality/valueThis paper provides useful information about corrosion behaviours of four coatings used for common boiler tubes. It shows with a practical explanation how the bare material and coatings react in corrosion simulated environments.

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In this study, atmospheric corrosion of copper exposed for 4 years in 12 different cities of Iran with various climatic characteristics was determined by weight loss method. Also, the corrosivity index of each city was classified using environmental factors according to the ISO 9223 standard. The results indicated good agreement between two approaches recommended by ISO standards. Accordingly, the corrosion rate of copper in Iran can be predicted according to the empirical kinetic equation (D = r corr t b ). Morphology, chemical composition and crystalline phases of patinas in cities with different kinetic behaviours were compared via SEM, EDS and XRD, respectively.

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PurposeThe purpose of this paper is to study the effects of temperature, dissolved oxygen (DO) and velocity of seawater on corrosion behavior of three copper‐based alloys (admiralty brass, aluminum brass and Cu‐5Ni alloy used in condenser tubes).Design/methodology/approachA series of electrochemical tests were carried out in seawater at different temperatures and DO contents using both stationary and rotating‐disc electrodes in order to investigate the corrosion behavior of alloys under these conditions.FindingsIt was found that admiralty brass exhibited a significantly higher corrosion rate and Cu‐5Ni alloy was more resistant to corrosion than were the brasses. With increasing temperature, the corrosion rates of the brasses increased. Selective zinc dissolution took place over the whole temperature range. Increasing temperature decreased the corrosion rate of Cu‐5Ni alloy in seawater due to formation of a passive film. The passivation of the alloy could be explained by the presence of greater proportion of nickel at the metal surface. Brasses, especially admiralty brass, exhibited higher corrosion rates in high concentrations of DO, whereas the Cu‐5Ni alloy was virtually immune to corrosion under such conditions. Increasing the water velocity increased the corrosion rate of admiralty brass but velocity had no effect on the corrosion rate of aluminum brass and Cu‐Ni alloy.Originality/valueThis paper provides information about corrosion behavior of three copper alloys used for common condenser tubes. The study fulfilled the objective of the investigation and contributes to research on corrosion behaviors of copper alloys in seawater.