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Research Paper

Fatigue Life Prediction for Crack Repair Welding in Bolted Joints of Gas Turbine Exhaust Casing

가스터빈 배기 케이싱 볼트 결합부의 균열 보수 용접에 대한 피로 수명 예측

Dae-Ock Kim1
,
Hyeokju Bae2
,
Hwangki Cho3*
,
Dongwoo Sohn4
김 대옥1
,
배 혁주2
,
조 황기3*
,
손 동우4
1Manager, Factory Automation Design Team of Tooling Center, Hyundai Motor Group, Ulsan, 44259, Korea
2Undergraduate Student, Department of Mechanical Engineering, Korea Maritime & Ocean University, Busan, 49112, Korea
3Postdoctoral Research Fellow, Department of Mechanical Engineering and Global R&E Program for Interdisciplinary Technologies of Ocean Renewable Energy, Korea Maritime & Ocean University, Busan, 49112, Korea
4Professor, Division of Mechanical Engineering, Korea Maritime & Ocean University, Busan, 49112, Korea
1현대자동차 툴링센터 자동화설계팀 매니저
2한국해양대학교 기계공학부 학사과정
3한국해양대학교 기계공학과 및 해양신･재생에너지 융합기술 글로벌 혁신인재 양성사업단 박사후연구원
4한국해양대학교 기계공학부 교수
*Corresponding Author
28 February 2025. pp. 63-73
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Abstract

Combined cycle power plants are frequently subjected to frequent startups and shutdowns due to the operational characteristics of gas turbines. In particular, thermal fatigue failure commonly occurs at the bolted joints of exhaust casings, as the high-temperature working fluid repeatedly comes into contact with ambient air at room temperature. For the purposes of cost and time efficiency, cracks that exert a negligible effect on plant operation are often repaired through welding before returning the component to service. However, the residual stress and plastic deformation induced during the welding process complicate the assessment of their effects on the structural integrity of the casing. Therefore, it is necessary to predict the fatigue life of crack-repaired welded casings to determine the permissible duration of their continued operation. In this study, finite element analysis and fatigue analysis were sequentially conducted to estimate the fatigue life based on the stress and strain amplitudes experienced under operating conditions. The results revealed that the fatigue life of the crack-repaired welded casing was reduced by up to 32% compared to that of an undamaged casing, representing the most pronounced reduction observed in the study. Furthermore, eight different weld bead sizes were investigated to account for variations in crack sizes. It was observed that the fatigue life decreased as the bead width and height decreased, while an increase in bead length further contributed to the reduction in fatigue life.

Keywords
gas turbine exhaust casing
crack repair welding
finite element method
residual stress
fatigue life

복합화력발전소는 가스터빈의 특성상 잦은 기동과 정지에 노출되며, 특히 배기부의 케이싱은 고온의 작동 유체가 실온 상태의 외기와 만나기 때문에 볼트 체결부에서 열 피로 파괴가 발생한다. 비용과 시간의 효율성을 위해 운전에 경미한 영향을 미치는 균열 부위는 용접 보수 작업 후 운용된다. 그러나 용접 과정에서 발생한 잔류 응력과 소성 변형이 케이싱에 미치는 영향을 조사하기 어렵기 때문에 균열 보수 용접 케이싱의 피로 수명을 예측하여 운전을 얼마나 지속할 수 있는지 연구할 필요가 있다. 본 연구에서 유한요소해석과 피로해석을 순차적으로 수행하여, 운전 조건에 따른 응력 및 변형률 진폭을 기반으로 피로 수명을 계산했다. 균열이 없는 건전 케이싱에 비해 균열 보수 용접 케이싱은 피로 수명이 최대 32% 감소했다. 또한 다양한 균열 형태를 고려하여 8가지 크기의 용접 비드를 사용했으며, 폭과 높이가 줄어들고 길이가 길어질수록 피로 수명이 감소하는 경향을 보였다.

키워드
가스터빈 배기부 케이싱
균열 보수 용접
유한요소해석
잔류 응력
피로 수명
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Information
  • Publisher :Computational Structural Engineering Institute of Korea
  • Publisher(Ko) :한국전산구조공학회
  • Journal Title :Journal of the Computational Structural Engineering Institute of Korea
  • Journal Title(Ko) :한국전산구조공학회 논문집
  • Volume : 38
  • No :1
  • Pages :63-73
  • Received Date : 2024-11-11
  • Revised Date : 2024-11-27
  • Accepted Date : 2024-11-27
  • DOI :https://doi.org/10.7734/COSEIK.2025.38.1.63
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