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51318-11142-Weld preferential high temperature sulfidation

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Very different corrosion behavior was observed between adjacent welds. This paper describes the investigation to identify the corrosion mechanism, trying to understand the influence of filler metal composition and welding parameters.

Product Number: 51318-11142-SG
Author: Matthieu Devallée / Xavier Roumeau / Francois Dupoiron
Publication Date: 2018
Industry: Petroleum Refining
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An extensive inspection campaign was executed in a West European refinery on circuits potentially subjected to high temperature low silicon carbon steel sulfidation (<0.1wt.%). This effort came on the top of the existing refinery sulfidation inspection plan for carbon steel piping. Ultrasonic testing (UT) measurements showed no excessive corrosion on any inspected components.

However, after these inspections were completed, a pinhole leak occurred on a weld in the Crude Distillation Unit (CDU) Heavy Gasoil (HGO) circuit. This circuit operates at 350°C (660°F), the HGO sulfur concentration ranges between 1.5 wt. % & 2.5 wt.%, and the Total Acid Number (TAN) is below 0.15 mg KOH/g. The affected piping spool was sent for metallurgical investigation, results indicating severe weld preferential corrosion whereas the surrounding base metals were not corroded.

Additional inspections were performed and results showed that 60% of this circuit circumferential welds were affected, with 30% below the retirement thickness and 30% that would have reached the retirement thickness before the next Turn-Around. Very different corrosion behavior was observed between adjacent welds, and even sometimes on the same weld, changing from no corrosion to heavy corrosion.

This paper describes the investigation that was performed to identify the corrosion mechanism, specifically trying to understand the influence of filler metal composition and welding parameters used on the corroded parts.

Key words: sulfidation, weld preferential corrosion, oxygen, silicon, carbon steel, welding process

 

 

An extensive inspection campaign was executed in a West European refinery on circuits potentially subjected to high temperature low silicon carbon steel sulfidation (<0.1wt.%). This effort came on the top of the existing refinery sulfidation inspection plan for carbon steel piping. Ultrasonic testing (UT) measurements showed no excessive corrosion on any inspected components.

However, after these inspections were completed, a pinhole leak occurred on a weld in the Crude Distillation Unit (CDU) Heavy Gasoil (HGO) circuit. This circuit operates at 350°C (660°F), the HGO sulfur concentration ranges between 1.5 wt. % & 2.5 wt.%, and the Total Acid Number (TAN) is below 0.15 mg KOH/g. The affected piping spool was sent for metallurgical investigation, results indicating severe weld preferential corrosion whereas the surrounding base metals were not corroded.

Additional inspections were performed and results showed that 60% of this circuit circumferential welds were affected, with 30% below the retirement thickness and 30% that would have reached the retirement thickness before the next Turn-Around. Very different corrosion behavior was observed between adjacent welds, and even sometimes on the same weld, changing from no corrosion to heavy corrosion.

This paper describes the investigation that was performed to identify the corrosion mechanism, specifically trying to understand the influence of filler metal composition and welding parameters used on the corroded parts.

Key words: sulfidation, weld preferential corrosion, oxygen, silicon, carbon steel, welding process

 

 

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51318-11625-Cracking of Duplex Stainless Steel in Refining Operations

Product Number: 51318-11625-SG
Author: Sudhakar Mahajanam / Fred Addington / Adarsh Ranganathan / Yuting Mao / Joanna Folse / Chloe Lins / Cesar Espinoza
Publication Date: 2018
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In this paper, case studies related to DSS cracking are presented specific to the refining industry. Two cases of chloride stress corrosion cracking (Cl-SCC) of 2205 DSS tubing are presented.
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51318-11071-Corrosion Behavior of Naphthenic Acids Isolated from Vacuum Gas Oil Crude Fractions

Product Number: 51318-11071-SG
Author: Yathish Kurapati / Winston Robbins / Gheorghe Bota / David Young
Publication Date: 2018
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Corrosion behavior of native naphthenic acids in two VGO fractions are compared with white oil solutions of the acids isolated from them by solid phase extraction (SPE). Tests are per the in-house “pretreatment-challenge” protocol on carbon steel and 5Cr steel samples.
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51318-11046-The investigation of Incoloy 800H Relaxation Crack Mechanisms

Product Number: 51318-11046-SG
Author: Yunjo Ro / Ihho Park / Gyutae Park / Jaewoong Kim
Publication Date: 2018
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In the present study, detailed microstructure of the crack-tip region of a failed tube was examined using SEM, TEM and EBSD to clarify the relaxation crack mechanism.  Details of the microstructural findings and a proposed mechanism of stress relief cracking will be discussed.

 
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