Testing of degradation of alloy 800 H in impure helium at 760 °C

The base metal, weld metal and heat affected zone specimen of alloy 800 H were exposed to impure helium at 760 °C for up to 1500 h. Helium impurities included 100 vppm of H2, 500 vppm of CO and 100 vppm CH4. The weight gain of alloy 800 H specimens were found to be higher than those of ferritic and austenitic stainless steel tested in similar environment. On the surface, corrosion product layers contained Cr and also Ti or Mn and other oxides. In some cases spalling of these layers was observed. Under corrosive layers the C, O, Ti, Cr and Al rich formations were also found. The exposure had no significant effect to hardness and micro hardness of tested alloy.