Abstract
Field reproduction of intergranular stress corrosion cracking (IGSCC) through two year exposure test in coal gas transport lines using U-bend specimens and laboratory reproduction of IGSCC were carried out in order to clarify the effects of environmental factors such as electrode potential, pH and temperature on crack initiation and propagation.
1) IGSCC of mild steel was reproduced by field exposure test in coal gas transport line. Cracks initiated at corrosion pits within crevices.
2) The critical depth of corrosion pits for IGSCC initiation was estimated about 70 μm by the application of the extreme value analysis.
3) The possible cracking region was assessed based on the high-and low potential sweep rates polarization curves and stability of the corrosion products as indicated by the potential/pH diagram.
4) Degradation of mild steel in the coal gas liquid was classified into four regions:
I) HE region (TGSCC): less noble than -1 000 mV vs S.C.E.
II) SCC region(IGSCC): -700- 500 mV vs S.C.E.
III) Fissure region (TG):-550-500mV vs S.C.E.
IV) General corrosion region : more noble than- 500 mV vs S.C.E.
