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Chemical Treatment To Mitigate Polythionic Acid SCC Without A Soda-Ash Wash: Laboratory And Plant Experience

Chemical Treatment To Mitigate Polythionic Acid SCC Without A Soda-Ash Wash: Laboratory And Plant Experience
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Different refiners have a variety of procedures in place for hydroprocessing reactor and reactor system shutdowns, depending on the scope of the work to be performed during the downtime. If activities are to be performed inside the reactor (e.g. inspection, maintenance, catalyst changeout, etc.) such that the reactor must be opened to air, shutdowns must include steps to address the various hazards. These same steps must also be applied to associated process equipment related to the reactor system susceptible to similar hazards and damage mechanisms. 

Product Number: 51322-17993-SG
Author: B.C. Rollins, K.J. Evans, N. Sutton, J. Esteban
Publication Date: 2022
Industries: Corrosion Monitoring and Control , Coatings
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$20.00
$20.00

A novel oxidative chemical treatment method is already being used to neutralize pyrophoric metal sulfides present in Hydroprocessing reactor systems. It is hypothesized that this treatment will similarly neutralize the iron sulfides which contribute to the formation of polythionic acids. A simple laboratory test has been developed to test the effectiveness of the chemical treatment. Previous experimental studies into polythionic acid stress corrosion cracking (PTASCC) have typically immersed stainless steel specimens in Saman’s solution, made by bubbling gaseous SO2 and H2S through the cell at controlled rates to produce a mixture of di-thionic through hexa-thionic acids along with sulfuric and sulfurous acids. In Saman’s solution, it can be difficult to obtain cracking even with the standard sensitizing heat treatments suggested in ASTM A2621. To circumvent these challenges, the current work uses standard U-bends (ASTM G302), coated with an air-sprayed suspension of iron sulfide powder. Specimens are suspended in saturated air (100% RH) at 50°C. Similarly, slow strain rate testing (SSRT) specimens were produced and tested using similar methods to identify the effect of exposure to FeS and various SCC mitigation and elimination treatments.

A novel oxidative chemical treatment method is already being used to neutralize pyrophoric metal sulfides present in Hydroprocessing reactor systems. It is hypothesized that this treatment will similarly neutralize the iron sulfides which contribute to the formation of polythionic acids. A simple laboratory test has been developed to test the effectiveness of the chemical treatment. Previous experimental studies into polythionic acid stress corrosion cracking (PTASCC) have typically immersed stainless steel specimens in Saman’s solution, made by bubbling gaseous SO2 and H2S through the cell at controlled rates to produce a mixture of di-thionic through hexa-thionic acids along with sulfuric and sulfurous acids. In Saman’s solution, it can be difficult to obtain cracking even with the standard sensitizing heat treatments suggested in ASTM A2621. To circumvent these challenges, the current work uses standard U-bends (ASTM G302), coated with an air-sprayed suspension of iron sulfide powder. Specimens are suspended in saturated air (100% RH) at 50°C. Similarly, slow strain rate testing (SSRT) specimens were produced and tested using similar methods to identify the effect of exposure to FeS and various SCC mitigation and elimination treatments.

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