Effect of microstructure on low temperature hydrogeninduced cracking behaviour of nickel-based alloy weld metals

Dissertation

Matias Ahonen

Research output: ThesisDissertationMonograph

Abstract

Various nickel-based materials are susceptible to low temperature crack propagation (LTCP) in simulated PWR (pressurized water reactor) water at a temperature range of about 50 to 150 °C. Experimental evidence from various sources shows that the hydrogen content of the water has a decreasing effect on the fracture resistance, thus LTCP is widely regarded as a hydrogen-induced phenomenon. This thesis concentrates on the LTCP phenomenon of Alloy 182, 82, 152 and 52 weld metals. The studied materials were both all-weld metals and dissimilar metal weld (DMW) mock-ups. The material conditions studied in this work were as-welded (AW), post-weld heat treated (PWHT) and high temperature water pre-exposed. The experimental work was divided in fracture mechanical testing in an environment, microstructural examination of fracture surfaces and hydrogen thermal desorption measurements. The obtained J-R test results show that Alloy 182 is the most susceptible nickel-based weld metal to LTCP, whereas Alloy 52 retains its high fracture resistance in hydrogenated water with moderate hydrogen content. The results obtained for all-weld metal Alloy 52 showed, however, a clear reduction of fracture resistance when tested at a high hydrogen content (100 cm3 H2/kg H2O), whereas narrow gap mock-up Alloy 52 DMW appeared to be less susceptible to LTCP in the corresponding environment. Hydrogen concentrations of Alloy 182 and 152 weld metal samples decrease during the high temperature water exposure, even when exposed to water containing 30 cm3 H2/kg H2O, and the fracture resistance values of Alloys 182 and 152 are improved. A clear relation between the low fracture resistance values and intergranular/interdendritic type of fracture was observed. The effect of grain boundary carbides and their hydrogen trapping properties are discussed based on the obtained SEM/EDS and thermal desorption spectroscopy results and a model was applied in order to determine the activation energies for hydrogen desorption of Alloys 182 and 52. The different LTCP behaviour of Alloy 182 and 52 weld metals is believed to be caused mainly by different types of carbides dominating the hydrogen-induced fracture. The carbides may have an effect on hydrogen distribution at the grain/dendrite boundaries and the availability of hydrogen close to the crack tip, by acting as trapping sites for hydrogen and by affecting the strain distribution at the grain boundary area.
Original languageEnglish
QualificationDoctor Degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Hänninen, Hannu, Supervisor, External person
  • Karlsen, Wade, Advisor
Award date18 Sep 2015
Place of PublicationEspoo
Publisher
Print ISBNs978-951-38-8338-6
Electronic ISBNs978-951-38-8339-3
Publication statusPublished - 2015
MoE publication typeG4 Doctoral dissertation (monograph)

Fingerprint

Welds
Nickel
Hydrogen
Microstructure
Metals
Crack propagation
Fracture toughness
Temperature
Dissimilar metals
Carbides
Water
Grain boundaries
Fracture testing
Thermal desorption spectroscopy
Mockups
Thermal desorption
Mechanical testing
Pressurized water reactors
Crack tips
Energy dispersive spectroscopy

Keywords

  • nickel-based weld metals
  • low temperature crack propagation
  • hydrogen trapping
  • fracture resistance

Cite this

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title = "Effect of microstructure on low temperature hydrogeninduced cracking behaviour of nickel-based alloy weld metals: Dissertation",
abstract = "Various nickel-based materials are susceptible to low temperature crack propagation (LTCP) in simulated PWR (pressurized water reactor) water at a temperature range of about 50 to 150 °C. Experimental evidence from various sources shows that the hydrogen content of the water has a decreasing effect on the fracture resistance, thus LTCP is widely regarded as a hydrogen-induced phenomenon. This thesis concentrates on the LTCP phenomenon of Alloy 182, 82, 152 and 52 weld metals. The studied materials were both all-weld metals and dissimilar metal weld (DMW) mock-ups. The material conditions studied in this work were as-welded (AW), post-weld heat treated (PWHT) and high temperature water pre-exposed. The experimental work was divided in fracture mechanical testing in an environment, microstructural examination of fracture surfaces and hydrogen thermal desorption measurements. The obtained J-R test results show that Alloy 182 is the most susceptible nickel-based weld metal to LTCP, whereas Alloy 52 retains its high fracture resistance in hydrogenated water with moderate hydrogen content. The results obtained for all-weld metal Alloy 52 showed, however, a clear reduction of fracture resistance when tested at a high hydrogen content (100 cm3 H2/kg H2O), whereas narrow gap mock-up Alloy 52 DMW appeared to be less susceptible to LTCP in the corresponding environment. Hydrogen concentrations of Alloy 182 and 152 weld metal samples decrease during the high temperature water exposure, even when exposed to water containing 30 cm3 H2/kg H2O, and the fracture resistance values of Alloys 182 and 152 are improved. A clear relation between the low fracture resistance values and intergranular/interdendritic type of fracture was observed. The effect of grain boundary carbides and their hydrogen trapping properties are discussed based on the obtained SEM/EDS and thermal desorption spectroscopy results and a model was applied in order to determine the activation energies for hydrogen desorption of Alloys 182 and 52. The different LTCP behaviour of Alloy 182 and 52 weld metals is believed to be caused mainly by different types of carbides dominating the hydrogen-induced fracture. The carbides may have an effect on hydrogen distribution at the grain/dendrite boundaries and the availability of hydrogen close to the crack tip, by acting as trapping sites for hydrogen and by affecting the strain distribution at the grain boundary area.",
keywords = "nickel-based weld metals, low temperature crack propagation, hydrogen trapping, fracture resistance",
author = "Matias Ahonen",
note = "BA2126 132 p. + app. 13 p.",
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language = "English",
isbn = "978-951-38-8338-6",
series = "VTT Science",
publisher = "VTT Technical Research Centre of Finland",
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address = "Finland",
school = "Aalto University",

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Effect of microstructure on low temperature hydrogeninduced cracking behaviour of nickel-based alloy weld metals : Dissertation. / Ahonen, Matias.

Espoo : VTT Technical Research Centre of Finland, 2015. 149 p.

Research output: ThesisDissertationMonograph

TY - THES

T1 - Effect of microstructure on low temperature hydrogeninduced cracking behaviour of nickel-based alloy weld metals

T2 - Dissertation

AU - Ahonen, Matias

N1 - BA2126 132 p. + app. 13 p.

PY - 2015

Y1 - 2015

N2 - Various nickel-based materials are susceptible to low temperature crack propagation (LTCP) in simulated PWR (pressurized water reactor) water at a temperature range of about 50 to 150 °C. Experimental evidence from various sources shows that the hydrogen content of the water has a decreasing effect on the fracture resistance, thus LTCP is widely regarded as a hydrogen-induced phenomenon. This thesis concentrates on the LTCP phenomenon of Alloy 182, 82, 152 and 52 weld metals. The studied materials were both all-weld metals and dissimilar metal weld (DMW) mock-ups. The material conditions studied in this work were as-welded (AW), post-weld heat treated (PWHT) and high temperature water pre-exposed. The experimental work was divided in fracture mechanical testing in an environment, microstructural examination of fracture surfaces and hydrogen thermal desorption measurements. The obtained J-R test results show that Alloy 182 is the most susceptible nickel-based weld metal to LTCP, whereas Alloy 52 retains its high fracture resistance in hydrogenated water with moderate hydrogen content. The results obtained for all-weld metal Alloy 52 showed, however, a clear reduction of fracture resistance when tested at a high hydrogen content (100 cm3 H2/kg H2O), whereas narrow gap mock-up Alloy 52 DMW appeared to be less susceptible to LTCP in the corresponding environment. Hydrogen concentrations of Alloy 182 and 152 weld metal samples decrease during the high temperature water exposure, even when exposed to water containing 30 cm3 H2/kg H2O, and the fracture resistance values of Alloys 182 and 152 are improved. A clear relation between the low fracture resistance values and intergranular/interdendritic type of fracture was observed. The effect of grain boundary carbides and their hydrogen trapping properties are discussed based on the obtained SEM/EDS and thermal desorption spectroscopy results and a model was applied in order to determine the activation energies for hydrogen desorption of Alloys 182 and 52. The different LTCP behaviour of Alloy 182 and 52 weld metals is believed to be caused mainly by different types of carbides dominating the hydrogen-induced fracture. The carbides may have an effect on hydrogen distribution at the grain/dendrite boundaries and the availability of hydrogen close to the crack tip, by acting as trapping sites for hydrogen and by affecting the strain distribution at the grain boundary area.

AB - Various nickel-based materials are susceptible to low temperature crack propagation (LTCP) in simulated PWR (pressurized water reactor) water at a temperature range of about 50 to 150 °C. Experimental evidence from various sources shows that the hydrogen content of the water has a decreasing effect on the fracture resistance, thus LTCP is widely regarded as a hydrogen-induced phenomenon. This thesis concentrates on the LTCP phenomenon of Alloy 182, 82, 152 and 52 weld metals. The studied materials were both all-weld metals and dissimilar metal weld (DMW) mock-ups. The material conditions studied in this work were as-welded (AW), post-weld heat treated (PWHT) and high temperature water pre-exposed. The experimental work was divided in fracture mechanical testing in an environment, microstructural examination of fracture surfaces and hydrogen thermal desorption measurements. The obtained J-R test results show that Alloy 182 is the most susceptible nickel-based weld metal to LTCP, whereas Alloy 52 retains its high fracture resistance in hydrogenated water with moderate hydrogen content. The results obtained for all-weld metal Alloy 52 showed, however, a clear reduction of fracture resistance when tested at a high hydrogen content (100 cm3 H2/kg H2O), whereas narrow gap mock-up Alloy 52 DMW appeared to be less susceptible to LTCP in the corresponding environment. Hydrogen concentrations of Alloy 182 and 152 weld metal samples decrease during the high temperature water exposure, even when exposed to water containing 30 cm3 H2/kg H2O, and the fracture resistance values of Alloys 182 and 152 are improved. A clear relation between the low fracture resistance values and intergranular/interdendritic type of fracture was observed. The effect of grain boundary carbides and their hydrogen trapping properties are discussed based on the obtained SEM/EDS and thermal desorption spectroscopy results and a model was applied in order to determine the activation energies for hydrogen desorption of Alloys 182 and 52. The different LTCP behaviour of Alloy 182 and 52 weld metals is believed to be caused mainly by different types of carbides dominating the hydrogen-induced fracture. The carbides may have an effect on hydrogen distribution at the grain/dendrite boundaries and the availability of hydrogen close to the crack tip, by acting as trapping sites for hydrogen and by affecting the strain distribution at the grain boundary area.

KW - nickel-based weld metals

KW - low temperature crack propagation

KW - hydrogen trapping

KW - fracture resistance

M3 - Dissertation

SN - 978-951-38-8338-6

T3 - VTT Science

PB - VTT Technical Research Centre of Finland

CY - Espoo

ER -