Thermal ageing and mechanical performance of narrow-gap dissimilar metal welds

Matias Ahonen, Sebastian Lindqvist, Esa Leskelä, Jari Lydman, Pekka Nevasmaa, Tommi Seppänen, Pentti Arffman, Ulla Ehrnsten, Teemu Sarikka, Roman Mouginot, Hannu Hänninen

Research output: Book/ReportReportProfessional

Abstract

NIWEL (Nickel-Base Alloy Welding Forum) project was primarily addressed to theneeds of the nuclear energy industry, and it was the fourth consecutive cooperative project on the dissimilar metal weld (DMW) topics. The main focus of the NIWEL project was to assess the effects of thermal aging on the performance of DMWs. Cooperation with PARENT (Program to Assess the Reliability of Emerging Nondestructive Techniques) program was also a part of the NIWEL project, and PARENT results are shortly presented in this report. The long-term behaviour of the DMWs is of particular interest in Finland, because the nuclear power plants are at critical stages of their lifetime: either beginning their operation or reaching lifetime extensions. In both cases, understanding of the aging phenomena is of utmost importance in order to ensure safe operation for lifetimes that can reach 60 years or even beyond that. With the exception of the fusion boundary region, the obtained microstructural characterization results on the weld metal and the base material did not show any clear indications of metallurgical changes. The fusion boundary region exhibits zones that are very narrow, some tens of micrometres or even less in width. The nanoindentation results show that the high local hardness mismatch between the soft carbon-depleted zone (CDZ) and very hard carbon-enriched zone in the Alloy 52 weld metal side of the fusion boundary, caused by PWHT, reduces due to thermalageing. Narrow-gap Alloy 52 DMW sustains its high performance, regarding ductile and brittle fracture properties adjacent to the fusion boundary between SA 508/Alloy 52 after thermal aging (10000 h at 400 °C) representative of 60 years of plant operation. Ductile-to-brittle transition temperature (T 42J ) measured after 10000 h aging is 12 °C, which gives a ΔT 42J of 47 °C as compared to the as-received material. Fracture toughness T0 was not significantly affected by thermal aging. Thus, it is assumed that thermal aging may promote brittle crack propagation and degrade material's capability to arrest the growing cracks at low temperatures, whereas the brittle crack initiation tendency of the material is not markedly affected. However, further investigations are needed to clarify the mechanisms explaining the differences. CDZ is the preferred crack path in all types of fracture mechanical tests applied in this study. However, crack deflections to the Alloy 52 weld metal side ofthe fusion boundary occur due to the small weld defects observed in the weld metal in tests, where the fracture mode is ductile.
Original languageEnglish
Place of PublicationEspoo
PublisherVTT Technical Research Centre of Finland
Number of pages189
ISBN (Electronic)978-951-38-8655-4
ISBN (Print)978-951-38-8656-1
Publication statusPublished - Jun 2018
MoE publication typeD4 Published development or research report or study

Publication series

NameVTT Technology
PublisherVTT
No.333
ISSN (Print)2242-1211
ISSN (Electronic)2242-122X

Fingerprint

Dissimilar metals
Thermal aging
Welds
Fusion reactions
Cracks
Metals
Carbon
Aging of materials
Ductile fracture
Brittle fracture
Nanoindentation
Crack initiation
Nuclear energy
Nuclear power plants
Superconducting transition temperature
Fracture toughness
Crack propagation
Welding
Hardness
Nickel

Keywords

  • dissimilar metal weld
  • Ni-base alloy
  • ageing
  • microstructure
  • fracture

Cite this

Ahonen, M., Lindqvist, S., Leskelä, E., Lydman, J., Nevasmaa, P., Seppänen, T., ... Hänninen, H. (2018). Thermal ageing and mechanical performance of narrow-gap dissimilar metal welds. Espoo: VTT Technical Research Centre of Finland. VTT Technology, No. 333
Ahonen, Matias ; Lindqvist, Sebastian ; Leskelä, Esa ; Lydman, Jari ; Nevasmaa, Pekka ; Seppänen, Tommi ; Arffman, Pentti ; Ehrnsten, Ulla ; Sarikka, Teemu ; Mouginot, Roman ; Hänninen, Hannu. / Thermal ageing and mechanical performance of narrow-gap dissimilar metal welds. Espoo : VTT Technical Research Centre of Finland, 2018. 189 p. (VTT Technology; No. 333).
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Ahonen, M, Lindqvist, S, Leskelä, E, Lydman, J, Nevasmaa, P, Seppänen, T, Arffman, P, Ehrnsten, U, Sarikka, T, Mouginot, R & Hänninen, H 2018, Thermal ageing and mechanical performance of narrow-gap dissimilar metal welds. VTT Technology, no. 333, VTT Technical Research Centre of Finland, Espoo.

Thermal ageing and mechanical performance of narrow-gap dissimilar metal welds. / Ahonen, Matias; Lindqvist, Sebastian; Leskelä, Esa; Lydman, Jari; Nevasmaa, Pekka; Seppänen, Tommi; Arffman, Pentti; Ehrnsten, Ulla; Sarikka, Teemu; Mouginot, Roman; Hänninen, Hannu.

Espoo : VTT Technical Research Centre of Finland, 2018. 189 p. (VTT Technology; No. 333).

Research output: Book/ReportReportProfessional

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AU - Ahonen, Matias

AU - Lindqvist, Sebastian

AU - Leskelä, Esa

AU - Lydman, Jari

AU - Nevasmaa, Pekka

AU - Seppänen, Tommi

AU - Arffman, Pentti

AU - Ehrnsten, Ulla

AU - Sarikka, Teemu

AU - Mouginot, Roman

AU - Hänninen, Hannu

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N2 - NIWEL (Nickel-Base Alloy Welding Forum) project was primarily addressed to theneeds of the nuclear energy industry, and it was the fourth consecutive cooperative project on the dissimilar metal weld (DMW) topics. The main focus of the NIWEL project was to assess the effects of thermal aging on the performance of DMWs. Cooperation with PARENT (Program to Assess the Reliability of Emerging Nondestructive Techniques) program was also a part of the NIWEL project, and PARENT results are shortly presented in this report. The long-term behaviour of the DMWs is of particular interest in Finland, because the nuclear power plants are at critical stages of their lifetime: either beginning their operation or reaching lifetime extensions. In both cases, understanding of the aging phenomena is of utmost importance in order to ensure safe operation for lifetimes that can reach 60 years or even beyond that. With the exception of the fusion boundary region, the obtained microstructural characterization results on the weld metal and the base material did not show any clear indications of metallurgical changes. The fusion boundary region exhibits zones that are very narrow, some tens of micrometres or even less in width. The nanoindentation results show that the high local hardness mismatch between the soft carbon-depleted zone (CDZ) and very hard carbon-enriched zone in the Alloy 52 weld metal side of the fusion boundary, caused by PWHT, reduces due to thermalageing. Narrow-gap Alloy 52 DMW sustains its high performance, regarding ductile and brittle fracture properties adjacent to the fusion boundary between SA 508/Alloy 52 after thermal aging (10000 h at 400 °C) representative of 60 years of plant operation. Ductile-to-brittle transition temperature (T 42J ) measured after 10000 h aging is 12 °C, which gives a ΔT 42J of 47 °C as compared to the as-received material. Fracture toughness T0 was not significantly affected by thermal aging. Thus, it is assumed that thermal aging may promote brittle crack propagation and degrade material's capability to arrest the growing cracks at low temperatures, whereas the brittle crack initiation tendency of the material is not markedly affected. However, further investigations are needed to clarify the mechanisms explaining the differences. CDZ is the preferred crack path in all types of fracture mechanical tests applied in this study. However, crack deflections to the Alloy 52 weld metal side ofthe fusion boundary occur due to the small weld defects observed in the weld metal in tests, where the fracture mode is ductile.

AB - NIWEL (Nickel-Base Alloy Welding Forum) project was primarily addressed to theneeds of the nuclear energy industry, and it was the fourth consecutive cooperative project on the dissimilar metal weld (DMW) topics. The main focus of the NIWEL project was to assess the effects of thermal aging on the performance of DMWs. Cooperation with PARENT (Program to Assess the Reliability of Emerging Nondestructive Techniques) program was also a part of the NIWEL project, and PARENT results are shortly presented in this report. The long-term behaviour of the DMWs is of particular interest in Finland, because the nuclear power plants are at critical stages of their lifetime: either beginning their operation or reaching lifetime extensions. In both cases, understanding of the aging phenomena is of utmost importance in order to ensure safe operation for lifetimes that can reach 60 years or even beyond that. With the exception of the fusion boundary region, the obtained microstructural characterization results on the weld metal and the base material did not show any clear indications of metallurgical changes. The fusion boundary region exhibits zones that are very narrow, some tens of micrometres or even less in width. The nanoindentation results show that the high local hardness mismatch between the soft carbon-depleted zone (CDZ) and very hard carbon-enriched zone in the Alloy 52 weld metal side of the fusion boundary, caused by PWHT, reduces due to thermalageing. Narrow-gap Alloy 52 DMW sustains its high performance, regarding ductile and brittle fracture properties adjacent to the fusion boundary between SA 508/Alloy 52 after thermal aging (10000 h at 400 °C) representative of 60 years of plant operation. Ductile-to-brittle transition temperature (T 42J ) measured after 10000 h aging is 12 °C, which gives a ΔT 42J of 47 °C as compared to the as-received material. Fracture toughness T0 was not significantly affected by thermal aging. Thus, it is assumed that thermal aging may promote brittle crack propagation and degrade material's capability to arrest the growing cracks at low temperatures, whereas the brittle crack initiation tendency of the material is not markedly affected. However, further investigations are needed to clarify the mechanisms explaining the differences. CDZ is the preferred crack path in all types of fracture mechanical tests applied in this study. However, crack deflections to the Alloy 52 weld metal side ofthe fusion boundary occur due to the small weld defects observed in the weld metal in tests, where the fracture mode is ductile.

KW - dissimilar metal weld

KW - Ni-base alloy

KW - ageing

KW - microstructure

KW - fracture

M3 - Report

SN - 978-951-38-8656-1

T3 - VTT Technology

BT - Thermal ageing and mechanical performance of narrow-gap dissimilar metal welds

PB - VTT Technical Research Centre of Finland

CY - Espoo

ER -

Ahonen M, Lindqvist S, Leskelä E, Lydman J, Nevasmaa P, Seppänen T et al. Thermal ageing and mechanical performance of narrow-gap dissimilar metal welds. Espoo: VTT Technical Research Centre of Finland, 2018. 189 p. (VTT Technology; No. 333).