Evaluation of an unusual superheated steam pipe failure

“…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%

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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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“…The experience with improved graphitization resistance (through increased activation energy) with increasing Mo in case of ductile irons [e.g., (Ref 32)] likely contributes to the general understanding that increased Mo in carbon steels increases graphitization resistance, permitting operating temperatures higher than for the plain carbon steels. Interestingly however, the most widely publicized graphitization-related (Ref 6,7,9,10,23,30)] and appear to be occurring at an increasing rate, with no such failures reported for C steel base metal.…”

Section: Results: C-mo Steelmentioning

confidence: 99%

An Updated Assessment of Graphitization of Steels in Elevated Temperature Service

Foulds

Shingledecker

2014

J. of Materi Eng and Perform

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Recent experience with damage and failure due to graphitization in electric power plant piping of carbon (C) and carbon-molybdenum (C-Mo) steel suggests that the previously developed time-temperature curves for graphitization prediction, first published over two decades ago, merit review. Recent data were combined with an exhaustive review of available literature. As with the earlier research, available experience data with reported approximate extent of graphitization and nominal service exposure conditions were analyzed for the predictions. When the data were combined, the database consisted of 281 data points. The data are in contrast to the roughly 40 points used in the prior research. The nature of the expanded C steel weldment database was such that the analysis could not effectively discriminate between all of the five graphitization levels used in previous research efforts. In this analysis, it was found that the level of graphitization as a function of time and temperature could be categorized into three broad ''risk'' ranges-defined as low, moderate, and significant, and that the curves delineating these ranges could be developed in a statistically conservative manner. These conservative time-temperature prediction curves are offered as an update to the previous time-temperature curves. Although the data for C-Mo steel base metal and weldments and on C steel base metal were inadequate for a full quantitative analysis, the experience with these materials cases is presented within the context of the C steel weldment risk curves and preliminary time-temperature conditions warranting concern for graphitization are offered. Finally, a partial validation of the risk curves is presented in examination of power plant piping that had operated for over 400,000 h.

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Evaluation of an unusual superheated steam pipe failure

Cited by 12 publications

References 3 publications

Graphitization in Low Alloy Steel Pressure Vessels and Piping

Graphitization in Low Alloy Steel Pressure Vessels and Piping

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

An Updated Assessment of Graphitization of Steels in Elevated Temperature Service

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