Abstract
Corrosion Resistant Alloys (CRAs) are routinely utilized to mitigate against the complex damage mechanisms encountered in refining operations that carbon and low alloy steels are highly susceptible to. However, CRA materials can suffer similar corrosion damage when improperly manufactured or exposed to aggressive environments. In this paper, three modes of CRA failure observed at a client’s site were analyzed in a lab and mitigation strategies proposed.
Tower trays near the top of a crude tower made of UNS S41008 martensitic stainless steel (SS) failed as a result of localized under-salt corrosion due to formation of amine hydrochloride salts. Appropriate crude pre-treatment was implemented to mitigate this corrosion mechanism.
UNS N06625 flexible hoses located at the inlet of a reformer in a hydrogen plant failed upon start-up during a turnaround. It was found that these materials were heavily sensitized with embrittling phases present at the austenite grain boundaries. Improper annealing processes at the manufacturing plant likely caused the sensitization of the microstructure.
Downstream of the reformers, UNS S30403 austenitic SS tube ends of the boiler feed water heat exchanger underwent a failure. The tube to fixed tube sheet seal weld failed as a result of fatigue cracking originating at a lack of weld deposit location. Ensuring a proper weld profile in compliance with the weld procedure would reduce such stress riser concentrations.
