Details
| Original language | English |
|---|---|
| Pages (from-to) | 189-200 |
| Number of pages | 12 |
| Journal | Engineering failure analysis |
| Volume | 97 |
| Publication status | Published - Mar 2019 |
| Externally published | Yes |
Abstract
Repetitive failures of high-temperature casing bolts of four 325 MW steam turbine units in a 1300 MW thermal power plant have been investigated. Ten of these Cr–Mo–V steel bolts were failed in less than two years, indicating the probability of repeatable phenomena of bolts. Working pressure and temperature of the turbine were 12.74 MPa and 535 °C, respectively. Failure analysis of the bolts including fractography, mechanical and microstructural analyses have been conducted. Results from mechanical tests indicated a dramatically reduction in impact toughness of the bolts. Results of fractography showed that the fracture mode is mostly intergranular brittle without any evidence of creep. Metallographic and chemical composition analyses of fracture surface showed the accumulation of carbides in grain boundaries. Two groups of specimens made of the failed bolts were undertaken different heat treatment including i) tempering and, ii) austenitizing and then tempering. It showed that the toughness properties of specimens were remarkably retrieved, specifically after the second heat treatment. Based on the results it was concluded that reversible temper embrittlement (RTE) were occurred in the bolts. Proposed criteria to prevent RTE were also applied and the results were discussed.
Keywords
- Cr-Mo-V steel, Failure analysis, Fractography, Turbine casing bolt
ASJC Scopus subject areas
- Materials Science(all)
- General Materials Science
- Engineering(all)
- General Engineering
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In: Engineering failure analysis, Vol. 97, 03.2019, p. 189-200.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Failure analysis of outer casing bolts of a 325 MW steam turbine
AU - Moshayedi, H.
AU - Moattari, M.
AU - Azizpour, K.
N1 - Publisher Copyright: © 2018
PY - 2019/3
Y1 - 2019/3
N2 - Repetitive failures of high-temperature casing bolts of four 325 MW steam turbine units in a 1300 MW thermal power plant have been investigated. Ten of these Cr–Mo–V steel bolts were failed in less than two years, indicating the probability of repeatable phenomena of bolts. Working pressure and temperature of the turbine were 12.74 MPa and 535 °C, respectively. Failure analysis of the bolts including fractography, mechanical and microstructural analyses have been conducted. Results from mechanical tests indicated a dramatically reduction in impact toughness of the bolts. Results of fractography showed that the fracture mode is mostly intergranular brittle without any evidence of creep. Metallographic and chemical composition analyses of fracture surface showed the accumulation of carbides in grain boundaries. Two groups of specimens made of the failed bolts were undertaken different heat treatment including i) tempering and, ii) austenitizing and then tempering. It showed that the toughness properties of specimens were remarkably retrieved, specifically after the second heat treatment. Based on the results it was concluded that reversible temper embrittlement (RTE) were occurred in the bolts. Proposed criteria to prevent RTE were also applied and the results were discussed.
AB - Repetitive failures of high-temperature casing bolts of four 325 MW steam turbine units in a 1300 MW thermal power plant have been investigated. Ten of these Cr–Mo–V steel bolts were failed in less than two years, indicating the probability of repeatable phenomena of bolts. Working pressure and temperature of the turbine were 12.74 MPa and 535 °C, respectively. Failure analysis of the bolts including fractography, mechanical and microstructural analyses have been conducted. Results from mechanical tests indicated a dramatically reduction in impact toughness of the bolts. Results of fractography showed that the fracture mode is mostly intergranular brittle without any evidence of creep. Metallographic and chemical composition analyses of fracture surface showed the accumulation of carbides in grain boundaries. Two groups of specimens made of the failed bolts were undertaken different heat treatment including i) tempering and, ii) austenitizing and then tempering. It showed that the toughness properties of specimens were remarkably retrieved, specifically after the second heat treatment. Based on the results it was concluded that reversible temper embrittlement (RTE) were occurred in the bolts. Proposed criteria to prevent RTE were also applied and the results were discussed.
KW - Cr-Mo-V steel
KW - Failure analysis
KW - Fractography
KW - Turbine casing bolt
UR - http://www.scopus.com/inward/record.url?scp=85059701209&partnerID=8YFLogxK
U2 - 10.1016/j.engfailanal.2019.01.044
DO - 10.1016/j.engfailanal.2019.01.044
M3 - Article
VL - 97
SP - 189
EP - 200
JO - Engineering failure analysis
JF - Engineering failure analysis
SN - 1350-6307
ER -