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Fitness For Purpose Evaluation Of Hydrogen Production Unit Centrifugally Cast Tubes: “Post Exposure” Metallographic And Mechanical Test

Picture for Fitness For Purpose Evaluation Of Hydrogen Production Unit Centrifugally Cast Tubes: “Post Exposure” Metallographic And Mechanical Test
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Product Number: 51321-16609-SG
Author: Marco De Marco/ Marco Palombo/ Gianluigi Cosso
Publication Date: 2021
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$20.00
$20.00

Centrifugal tubes resistant to high temperatures, whose nominal composition is 25 Cr, 35 Ni, 1 to 1.5 Nb, 0.4 C, Fe balance, have been examined both from a mechanical/metallurgic point of view and a design one in relation to the construction of furnaces to produce hydrogen by catalytic reforming (temperature 850 to 950°C and circumferential stress 10 to 15 MPa for approximately 11 years, i.e. 100,000 hours). An assessment of the Fitness for Purpose that considers the characteristics of the material as supplied might overestimate in a non-conservative way the material reliability. Therefore, based on a vast collection of results obtained with this type of material, the data acquired were gathered in a single method, which can be used as a practical tool for Fitness for Purpose evaluations and to proper schedule maintenance and inspections. Specifically, three different states of degradation of the tube material have been identified: as cast (new material, as supplied by the manufacturer), slightly degraded and moderately degraded. The mechanical properties at ambient temperature (hardness and upper yield point), the microstructure and creep resistance have been considered, on the whole, to define Larson- Miller stress-parameter curves for each of the above conditions. The method obtained allows for a reliable assessment of the residual life and more accurate planning of inspections and/or replacements of tubes showing greater degradation, considering the most appropriate resistance curve (intended as the relationship between acting stress and the Larson-Miller parameter) for the actual conditions of the material, identified on tubes in operation with diametral measurements, hardness tests, metallographic replicas or, if possible, fast non-time-dependent destructive tests (e.g. micrographs).

Keywords: Steam reforming, furnace, residual life, creep, hydrogen production, Larson-Miller Parameter, Asset Integrity Management, inspection planning

Centrifugal tubes resistant to high temperatures, whose nominal composition is 25 Cr, 35 Ni, 1 to 1.5 Nb, 0.4 C, Fe balance, have been examined both from a mechanical/metallurgic point of view and a design one in relation to the construction of furnaces to produce hydrogen by catalytic reforming (temperature 850 to 950°C and circumferential stress 10 to 15 MPa for approximately 11 years, i.e. 100,000 hours). An assessment of the Fitness for Purpose that considers the characteristics of the material as supplied might overestimate in a non-conservative way the material reliability. Therefore, based on a vast collection of results obtained with this type of material, the data acquired were gathered in a single method, which can be used as a practical tool for Fitness for Purpose evaluations and to proper schedule maintenance and inspections. Specifically, three different states of degradation of the tube material have been identified: as cast (new material, as supplied by the manufacturer), slightly degraded and moderately degraded. The mechanical properties at ambient temperature (hardness and upper yield point), the microstructure and creep resistance have been considered, on the whole, to define Larson- Miller stress-parameter curves for each of the above conditions. The method obtained allows for a reliable assessment of the residual life and more accurate planning of inspections and/or replacements of tubes showing greater degradation, considering the most appropriate resistance curve (intended as the relationship between acting stress and the Larson-Miller parameter) for the actual conditions of the material, identified on tubes in operation with diametral measurements, hardness tests, metallographic replicas or, if possible, fast non-time-dependent destructive tests (e.g. micrographs).

Keywords: Steam reforming, furnace, residual life, creep, hydrogen production, Larson-Miller Parameter, Asset Integrity Management, inspection planning

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