MASTER THESIS Investigation of High-temperature Corrosion Behaviour of P9 steel and Alloy 800HT in HCl and H2S Atmospheres with Low Oxygen Pressure

The corrosion behaviour of Alloy 800HT and P9 steel was investigated in atmospheres mimicking the thermal cracking process of anthropogenic resources. The testing gas consisted of 3.8 vol.% HCl, 2.8 vol.% H2, 1.9 vol.% CO2, 0.3 vol.% CO, 0.02 vol.% H2S and N2 as balance. Additionally, experiments without HCl as corrosive component were performed to get more information about the influence of HCl on the high-temperature corrosion of the samples in mixed-gas atmospheres. The tests were performed between 24, 72 and 240 hours at 480 °C, 580 °C and 680 °C, respectively. All samples showed solid corrosion products on their surfaces. Selected specimens were cold mounted to analyse the microstructure of the corrosion layers. SEM (scanning electron microscopy) / EDX (energy-dispersive X-ray spectroscopy) were used as complementary analytical methods for investigation of the corrosion process. Additionally XRD (X-ray powder diffraction) analyses of single corrosion products were made. Mass loss determinations for every specimen were performed as well. The P9 steel showed an increasing mass loss with rising temperature, whereas alloy 800HT was quite resistant against HCl attack; only at lower temperatures the sulfidation of nickel led to an increase of the mass loss. The corrosion layers on the samples typically consisted of sulfide crystals on the outer layer, followed by an oxide/chloride scale with material depletion beneath it.