A refinery experienced an unexpected shutdown due to a power outage linked to an extreme weather condition. The loss of power lasted for 1 week and the utilities were down for a total of 2 weeks. As a consequence of the steam tracing being down for that long, heavy products like the Vacuum Tower Bottom (VTB) solidified in the piping systems. During the unplugging effort, a leak was discovered on a VTB piping circuit constructed of austenitic stainless steel. Therefore, before beginning to restart the unit and the refinery, an investigation had to be carried out to identify the origin and extent of the problem.

The cracking was initiated from the inside and propagated in a short period of time. The failure investigation identified the stress corrosion cracking by chlorides to be the mechanism involved, due to an inappropriate product used during the unplugging of the circuit. The consequences could have been much worse as cracking only affected a limited part of the circuit but could have impacted it entirely which would have resulted in a much higher economic impact for the plant. In circumstances like the one encountered after a major power outage where the resources are stretched in a short timeframe between the different recovery efforts, the need of having guidance for the “unplugging of heavy product lines” is key to ensure the integrity of equipment and the safety of people.

This paper describes the investigation that was performed to identify the corrosion mechanism involved and especially the reason why it took place.

Subject
Circuits, Water, Piping, Crack initiation, Transgranular stress corrosion cracking, Inspection, Refineries, Stainless steel, Caustic stress corrosion cracking, Steam, Chlorides, Stress corrosion cracking, Chloride stress corrosion cracking
Keywords:
stress corrosion cracking, stainless steel, unplugging, chlorides
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2021
Association for Materials Protection and Performance (AMPP)
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