Graphitization in Low Alloy Steel Pressure Vessels and Piping

Pérez, Iván Uribe; Silveira, T.L. da; Silveira, Tito Fernando da; Furtado, H.C.

doi:10.1007/s11668-010-9414-z

Cited by 16 publications

(6 citation statements)

References 4 publications

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“…5(h) and 5(i), and the ~100-μm diameter of the spherical graphite formed after 85 699.2 h at 773 K is consistent with those of similar previously reported. 5,6,16) However, in this study, elongated graphite are also observed at the grain boundaries, as shown in Figs. 5(a)-5(g); notably, these confirm the occurrence of graphitization at 673 K. This indicates that graphitization at 673 K can be a concern in service materials, although the ASME Code and other specifications describe graphitization as a phenomenon to consider above 698 K. 4,9,10) Hereafter, these two types of precipitated graphite will be called "elongated graphite" and "spherical graphite".…”

Section: Discussionmentioning

confidence: 42%

“…The morphology of graphite particles that appear in carbon steels by long-term exposure to high temperatures is usually spherical, 2,3,[5][6][7]16) as shown in Figs. 5(h) and 5(i), and the ~100-μm diameter of the spherical graphite formed after 85 699.2 h at 773 K is consistent with those of similar previously reported.…”

Section: Discussionmentioning

confidence: 99%

“…The chain-like aligned graphite particles tend to appear along weld heataffected zones and cause failure by their linkage across the matrix. 2,5,6) It is also implied that deformed microstructures are more susceptible to graphitization. 2,3,7) In addition, the strength of steel is reduced by the disappearance of pearlite.…”

Section: Introductionmentioning

confidence: 99%

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Graphitization Behaviors of Creep-ruptured 0.3% Carbon Steel at 673 to 773 K

et al. 2021

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Graphitization in carbon steels must be prevented because it reduces the amount of carbon in the matrix, which degrades the material performance due to loss in strength. In addition, when graphite particles are aligned, they can cause fracture by their linkage. The safety management standards for carbon steels in high-temperature applications state that graphitization should be considered at 698 K and above. The number of reported cases on graphitization in steels below 698 K is limited, and the mechanism has not yet been well investigated. This paper reports the finding of unprecedented graphitization at 673 K in creep-ruptured carbon steel and an elongated form of graphite that appears after a much shorter time at 673-773 K than other previously reported times. Furthermore, the formation mechanism of this elongated graphite is discussed. Dislocations and inclusions in the vicinity of grain boundaries may facilitate graphitization kinetics at these temperatures.

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Section: Discussionmentioning

confidence: 42%

Section: Discussionmentioning

confidence: 99%

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Graphitization Behaviors of Creep-ruptured 0.3% Carbon Steel at 673 to 773 K

et al. 2021

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“…1) In addition, as cementite is a metastable phase in the Fe-C system, it decomposes into iron and carbon during long-term exposure to elevated temperatures, results in the precipitation of graphite. This phenomenon is called graphitization and the occurrence is reported in low carbon 2,3) , medium carbon 4) , and high carbon steels. 5) Graphitization is a time-and temperature-dependent phenomenon that degrades the mechanical properties of the steels and increases the risk of component failure used at elevated temperatures.…”

Section: Introductionmentioning

confidence: 99%

Prediction of Graphitization Behavior during Long-Term Creep in Carbon Steels

2023

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Carbon steels with ferrite and pearlite microstructures suffer from graphitization by the decomposition of cementite when exposed to elevated temperatures for long periods. Graphitization degrades the mechanical properties of the steels and increases its risk of failure. Therefore, by considering the extended life span of a thermal power plant, where carbon steels are used at elevated temperatures, evaluation of graphitization risk is necessary. This study evaluates the effect of temperature, stress, time, and chemical composition for both elongated and spherical graphitization using logistic regression of previously reported graphitization conditions in long-term creep ruptured specimens and establishes a prediction formula for graphitization occurrence. In addition, the accuracy of the prediction formula was validated by investigating the graphitization behavior of other carbon steels.

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“…For examples, carbon steel tubes can be subjected to "spheroidization" to which lamellar iron carbides decompose into spheroidized iron carbides (Chatterjee,2012, Liu et al , 2017. Furthermore, these tubes can also be susceptible to "graphitization" where iron carbides dissociate to form ferrite matrix and nodular graphite (Perez , 2011). Both microstructural changes negatively affect the mechanical properties.…”

Section: Introductionmentioning

confidence: 99%

A metallurgical investigation on a failed superheater tube used in a thermal biomass power plant

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et al. 2021

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This article described the investigation of the failed superheater tube made of SA210 Grade C used in a biomass power plant. Visual inspection, microstructural examination, chemical analysis and hardness measurement were employed to analyze the causes of the superheater tube failure. Results from the investigation showed that the major cause of this failure was mainly related to the long-term overheating, resulting in the occurrence of the excessive thermal oxidation and graphitization. The excessive thermal degradation accelerated the reduction of the wall tube and promoted the build-up of the stress acting on the tube. Graphitization degraded the microstructure of the tube, reducing the mechanical performance of the tube. The combined effects from the severe thermal oxidation and graphitization attributed to the premature failure of the tube. It is therefore advised to use the correct material, SA213 T22, in the failed section. Material specification examination for superheater regions prior to tube installations should be performed to avoid the use of the inappropriate material. The temperature monitoring and mapping in this section were also suggested.

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Graphitization in Low Alloy Steel Pressure Vessels and Piping

Cited by 16 publications

References 4 publications

Graphitization Behaviors of Creep-ruptured 0.3% Carbon Steel at 673 to 773 K

Graphitization Behaviors of Creep-ruptured 0.3% Carbon Steel at 673 to 773 K

Prediction of Graphitization Behavior during Long-Term Creep in Carbon Steels

A metallurgical investigation on a failed superheater tube used in a thermal biomass power plant

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