Abstract: The lower head of the steam water separator of the external blast regeneration adsorption dryer equipped on the high sulfur air compressor suddenly breaks and falls off during use. The macro morphology, chemical composition, microstructure, micro morphology and corrosion products of failure fracture were comprehensively analyzed by direct reading spectrometer, metallographic microscope, scanning electron microscope and energy dispersive spectrometer. The results show that the failure mode of the head was erosion corrosion fracture. When the steam water mixture containing sulfide and chloride washed the head at high speed, the alternating erosion failure process of passivation, fluid erosion, electrochemical corrosion and repassivation occured. Because of the existence of banded structure, the head has anisotropy, which intensifies erosion corrosion cracking.