Abstract: Aiming at the problem discovered in periodic inspection that corrosion holes were found densely below the liquid level of the reflux tank of the PTA plant and some of the corrosion holes had cracking, this paper analyzes the causes of the defect through production process analysis, medium and material research, crack field phased array detection, metallographic examination and comprehensive damage modes identification of the reflux tank. Meanwhile, the paper makes a safety assessment on the defect according to the standards of TSG21-2016 Supervision Regulation on Safety Technology for Stationary Pressure Vessel and GB/T 19624－2004 Safety Assessment for in-service Pressure Vessels Containing Defects. Then, the paper formulated the defects treatment methods.

Key words: PTA plant, reflux tank, stress corrosion cracking/SCC, corrosion pit, damage modes identification, safety assessment