Keywords: Stainless Steel, Caustic Soda, Corrosion, Inclusions, Stress Corrosion Cracking
<p lang="en-GB" class="western" style="margin-bottom: 0.17in; line-height: 100%;"> Paper deals with the case studies of stainless steel piping corrosion in caustic soda transfer lines at a hydrocarbon processing plant, in Asian region. The lines were in service of transferring the caustic soda solution from storage tank farm to different process units, for subsequent use in reaction vessels. To maintain a minimum temperature of fluid to avoid its precipitation, the lines were accompanied with a steam heat-tracer, throughout the line route. The material of construction (MOC) of line was stainless steel type 316. After a period of about 3.5 years, 2” caustic line suffered fluid leakage, which was noticed through significant salt accumulation over insulation at one location. A valve was also noticed to leak through a weld at a 1.5” distribution line. The affected components were removed from service and subjected to detailed inspection and laboratory investigation, using advanced tools of metallurgical analysis and characterization. It was found that leakage in 2” line has occurred due to poor workmanship used during repair of a manufacturing defect at the affected location and leakage of valve has taken place due to use of improper welding practice (in case of subjected weld). In addition, significant role of metallurgical defects in the parent metal, were also disclosed to result in the observed failures. In addition, the contribution of process excursions can’t be completely ruled out. Finally, remedial measures are given to avoid the recurrence of such failure.</p>
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