Metallurgical aspects of a blowdown pipe failure in a petrochemical plant

摘要

This study investigates the premature failure of AISI 304 stainless steel pipe in a blowdown unit used between boiler and blowdown vessel in a petrochemical plant. The first leak was reported in the elbow after a few weeks of service. The leak was repaired. The repaired unit showed a crack in the pipe in the vicinity of the elbow only after 6 months of service at 150 degrees C. Failed pipe and elbow were taken out of the system, in order to conduct a failure analysis. Visual inspection, optical and electron microscopy, electron dispersive spectroscopy (EDS) analysis, and hardness measurements were employed to identify failure cause. Results showed that intergranular stress assisted cracking facilitated by grain drop, due to oxidation at grain boundaries, were the main failure mechanisms. Possible mitigation strategies are suggested.