Failure Analysis of Rapid Crack Propagation on CO<sub>2</sub> Low Pressure Flash Column

Low Pressure (LP) flash column is one of the equipment at CO 2 removal plant, operated since 2003 with a design pressure and temperature of 1.75 kg/cm 2 g and 90 °C, respectively. The LP flash column functions as a place for the CO 2 gas to be absorbed by aMDEA and produces lean amine. At turn around in 2021, a crack with a length approximately 5 cm was found on the inside of the top part of the LP flash column (shell area near weld). Repairment was carried out by providing a crack stopper on the crack tip, gouging, non-destructive evaluation (NDE) and welding. However, when NDE was applied, new cracks appeared around the initial crack. Some inspection and testing were further carried out to find the root cause and appropriate repair method. The results indicate that the crack has a branching pattern and its propagation cuts through trans-granular grain. Upon further analysis, there was unusually higher chloride content on the crack surface area and hardness value was higher (202-209 HB) than standard hardness value for ASTM A240-304L (≤ 201 HB) which indicates the crack was caused by chloride stress corrosion cracking (Cl-SCC). Excessive load or stress caused cracks to propagate rapidly and uncontrolled. Based on ASME PCC-2, the Butt Weld Insert Plate was selected as the repair method due to its suitability for a wide range of defects, its ability to reduce crack propagation and its provision of a permanent repair solution. Another NDE was conducted after the repair to ensure that the repairs were properly executed, with no welding defects or new cracks in the repair area. The results confirmed that there were no defects in the shell material following the installation of the butt weld insert plate.