Corrosion Behavior of Different Materials in Environment of De-heavy Oil Column for Ethylene Glycol Production Plant from Syngas

Corrosion behavior of five materials in the environment of de-heavy oil column for ethylene glycol production plant from syngas (nitric acid mass fraction of 2%-8%, temperature of 116℃) was investigated by coupon corrosion testing on-site. The surface morphology and the depth of intergranular corrosion of the coupons after corrosion test were examined by scanning electron microscope (SEM) and optical microscope (OM). The results indicate that the stainless steel 904L and nitric acid grade stainless steel KY702, whose general corrosion rates were no more than 0.006 mm/a, had good general corrosion resistance, but they had very slight intergranular corrosion sensitivity, while the stainless steels 304L, 254SMO and nickel based alloy 825 had obvious intergranular corrosion sensitivity. Sensitization could affect seriously the intergranular corrosion of nickel based alloy 825 and stainless steel 254SMO. The intergranular corrosion rates of the sensitized stainless steel 254SMO and nickel based alloy 825 increased to 15 times and 16 times, respectively, as compared with their solid solution states.