Failure of SS 304H Convection Preheater Coil of Hydrogen Reformer Due to Polythionic Acid Stress Corrosion Cracking (PASCC)

摘要

Failure of austenitic stainless steel type SS304H (UNS S30409) due to Polythionic Acid Stress Corrosion Cracking (PASCC) is not a common phenomena in recent times of petroleum refining industry as proper material selection and shutdown procedures are adopted. However, such cracking is still prevailing sporadically due to certain design deficiencies and not following shut down procedure meticulously. The coil had first time failed at the weld joint in 1992 shut down after 8 years of service and the same was repaired. In March 2009 shutdown, the recurrence of such cracks were observed again hence investigated. This paper deals with the failure investigation and metallographic studies. Detailed analysis including Scanning Electron Microscopy along with Energy Dispersive Spectroscopy were carried out. Failure of SS 304H tube is attributed to Polythionic Acid Stress Corrosion Cracking. Remedial measures such as neutralization followed by nitrogen purging prior to shutdown is also discussed in the paper.