Abstract:
Surface engineering of ASTM A213 TP347H boiler steel was done by detonation-gun spraying of a
Ni – 20Cr coating with the aim to enhance the corrosion resistance of the steel. High-temperature
corrosion behaviour was investigated for the uncoated and coated boiler steel in a simulated boiler
environment (Na2SO4 – 60%V2O5) at 900 C for 50 cycles. Each cycle consisted of 1 hour heating in
the silicon carbide tube furnace followed by 20 minutes cooling in air. Measurement of mass change
was used to approximate the kinetics of corrosion. X-ray diffraction (XRD) and scanning electron
microscopyyenergy dispersive spectroscopy (SEMyEDS) were used to characterise the corrosion
products. To ascertain the rate of corrosion the parabolic rate constants (kp) were obtained from the
slope of the linear regression fitted of (cumulative weight gainyarea)2 versus number of cycles for the
uncoated as well as the coated substrates. It was observed that the behaviour of uncoated steel was
not parabolic and it suffered corrosion in the form of peeling up and spallation of its oxide scale. On
the contrary, the Ni – 20Cr coated steel followed a parabolic rate law and showed reduced rates of
corrosion in comparison with its uncoated counterpart. The loss of material owing to high temperature
corrosion of the steel was reduced appreciably after the application of the coating
