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Effect of Carbide Equilibrium State on the High Temperature Hydrogen Attack Resistance of2.25Cr-1Mo Steel

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Steel components in refineries and petrochemical plants are exposed to conditions of temperatures higher than 200°C with high pressures of hydrogen. Such conditions avail the driving force needed for the hydrogen to dissociate and penetrate the steel surface. Once the atomic or nascent hydrogen is within the steel microstructure, it can react with the carbon present, usually in carbides, to form methane gas within the steel structure as suggested by the below reactions:
[C]α + 4[H]α → [CH4]gas (1)
where α refers to ferrite.

Product Number: MECC23-20193-SG
Author: M. A. M. Alshahrani;
Publication Date: 2023
$20.00
$20.00
$20.00

High temperature hydrogen attack is a damage mechanism that threatens the integrity of critical steel components in petrochemical plants and refineries when the hydrogen diffuses into the steel and reacts with the carbides within to produce pores containing methane. With the motivation of understanding the role of carbide stability on the reaction with hydrogen, samples of a classic 2.25Cr-1Mo steel were subjected to a variety of heat treatments that generate a variety of carbides, prior to exposure to highpressure hydrogen in an autoclave. Using quantitative carbide and microstructural characterisation, it has been possible to demonstrate the roles of four variables: (a) the non-equilibrium chemical composition of carbide; (b) the fraction of the carbide that is closest to the thermodynamic equilibrium state; (c) the location of where the depletion preferentially occurs.

High temperature hydrogen attack is a damage mechanism that threatens the integrity of critical steel components in petrochemical plants and refineries when the hydrogen diffuses into the steel and reacts with the carbides within to produce pores containing methane. With the motivation of understanding the role of carbide stability on the reaction with hydrogen, samples of a classic 2.25Cr-1Mo steel were subjected to a variety of heat treatments that generate a variety of carbides, prior to exposure to highpressure hydrogen in an autoclave. Using quantitative carbide and microstructural characterisation, it has been possible to demonstrate the roles of four variables: (a) the non-equilibrium chemical composition of carbide; (b) the fraction of the carbide that is closest to the thermodynamic equilibrium state; (c) the location of where the depletion preferentially occurs.

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