Abstract: This paper makes an in-depth analysis on the crack failure of column tray of the atmospheric tower in CDU & VDU. Analysis methods for material failure such as scanning electron microscopy and crystal phase microscopy are adopted to analyze the microstructure of the base metal of the failed tray caused by crack. It is determined that the failure is caused by stress corrosion cracking resulting from the tensile stress and Cl- interaction at the bottom of the tray; meanwhile, the alternating fatigue load due to the up-and-down vibration of the tray results in fatigue cracks, which is one of the reasons for the tray crack. Based on the main reasons for the cracking of the tray, the paper has developed scientific control measures to ensure the safe and reliable operation of the atmospheric tower.

Key words: atmospheric-vacuum distillation unit, tray, stress corrosion cracking/SCC, fatigue crack