At the KEMA laboratories, three types of corrosion concerning heat exchangers in coal gasifiers were studied in detail: (1) resistance of materials to general corrosion (sulfidation); (2) down-time corrosion; and (3) interaction between stress/strain and corrosion (corrosion-assisted cracking). A combination of optical and scanning electron microscopy and special sample preparation techniques gave excellent information about the corrosion mechanisms of sulfidation and down-time corrosion. The slow strain rate testing technique was applied to classify materials according to resistance to corrosion-assisted cracking. Critical temperatures for cracking were determined.