Fractographic Signs of Gigacycle Fatigue and Hydrogenation of Heat-Resistant Steels after Long-Term Operation

We study the structure and distribution of hydrogen in 16GNM steel after its long-term (∼28 ⋅ 10 4 h) operation in the body of a drum-boiler after a large number of startups and shutdowns (1830) destroyed in the course of pressure testing after maintenance. We establish the distribution of local hy...

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Bibliographic Details
Published in:	Materials science (New York, N.Y.) Vol. 56; no. 6; pp. 727 - 738
Main Authors:	Smiyan, О. D., Student, О. Z.
Format:	Journal Article
Language:	English
Published:	New York Springer US 01-05-2021 Springer Springer Nature B.V
Subjects:	Boilers Characterization and Evaluation of Materials Chemistry and Materials Science Crack propagation Equipment and supplies Fatigue failure Fracture surfaces Heat resistant steels Heating High temperature Hydrogen Hydrogenation Low cycle fatigue Materials Science Metal fatigue Shutdowns Solid Mechanics Structural Materials hydrogenation of the metal fractographic signs of gigacycle fatigue hydrogen fracture mechanism sites of fracture initiation
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Summary:	We study the structure and distribution of hydrogen in 16GNM steel after its long-term (∼28 ⋅ 10 4 h) operation in the body of a drum-boiler after a large number of startups and shutdowns (1830) destroyed in the course of pressure testing after maintenance. We establish the distribution of local hydrogen content in different zones across the thickness of the wall and show that hydrogenation affects the mechanism of low-cycle fatigue fracture of the metal. However, we also recorded fractographic signs of gigacycle fatigue. In particular, fracture processes were initiated not from the surface of the boiler body but at a certain depth from the surface in agreement with the distribution of hydrogen in the wall. Moreover, we discovered atypical rounded fragments on the fracture surface caused by the simultaneous influence of hydrogen and gigacycle fatigue via the insignificant fluctuations of temperature and stresses. Their number noticeably exceeds the number of controlled shutdowns but is consistent with insignificant deviations of the technological parameters from the regulated requirements, which are, as a rule, not recorded in the process of operation. This specific feature should be taken into account in the evaluation of the resource of equipment operating under the conditions of combined influence of the elevated temperatures and hydrogenation of the metal.
ISSN:	1068-820X 1573-885X
DOI:	10.1007/s11003-021-00489-3