Application of Laser Thermography for Detection of Weld Cracks in Steel Structures

Soonkyu Hwang; Chisung Kim; Hoon Sohn

doi:10.22725/JSRP.2025.3.1.1

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2025 Vol.3, Issue 1 Next Page

Research Article

Application of Laser Thermography for Detection of Weld Cracks in Steel Structures 강구조물 용접균열 검출을 위한 레이저 열화상 시스템 응용

30 June 2025. pp. 1-8

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Abstract

This study presents a laser-based infrared thermographic technique for detecting weld cracks in steel bridge structures. To enable field application, the system was redesigned to be lightweight and portable by simplifying hardware and data processing components. The system includes a laser excitation unit, an infrared camera, and a control unit, integrated for synchronized operation. Field tests were conducted on U-rib welded joints of an in-service steel box girder bridge. The proposed method visualized fine cracks (30–80 µm) by analyzing abnormal heat propagation patterns and applying phase-locked image processing. To improve detection accuracy, a threshold was determined using a Weibull distribution fit, and image noise was reduced through median filtering. Results confirmed that the system can detect subsurface cracks beneath coating layers in a non-contact and real-time manner. This study demonstrates the feasibility of using active thermography for on-site inspection of welded joints, contributing to automated maintenance of large-scale steel structures.

Keywords

laser thermography

lock-in amplitude

non-destructive testing

weld crack detection

본 연구는 강교량 구조물의 용접부 균열을 비접촉 방식으로 탐지하기 위한 레이저 기반 열화상 기법을 제안한다. 레이저 열화상 기법의 현장 적용을 위해 시스템 하드웨어를 경량화하고 데이터 처리 절차를 간소화하여 휴대 및 운용성을 강화하였다. 제안된 시스템은 레이저 가진부, 열화상 카메라, 제어부로 구성되며, 동기화된 방식으로 작동한다. 실제 강박스거더교량의 U-rib 용접부를 대상으로 현장 실험을 수행하였으며, 레이저 가진에 따른 표면 열전달 패턴 분석을 통해 균열 폭 30–80 µm 수준의 미세 균열을 시각화하였다. 영상처리 과정에서는 위상잠금 기법과 Weibull 분포 기반 임계값 산정, 중간값 필터링을 적용하여 영상 노이즈를 제거하고 균열 영역을 효과적으로 추출하였다. 실험 결과, 도막층 아래 존재하는 균열을 실시간으로 비접촉 탐지할 수 있음이 확인되었으며, 제안 기술이 현장 용접균열 탐상 기술로 활용될 수 있는 가능성을 제시한다.

키워드

레이저 열화상

위상잠금 진폭

비파괴검사

접합부 용접 균열

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Information

Publisher :Korean Institute of Bridge and Structural Engineers
Publisher(Ko) :한국교량및구조공학회
Journal Title :Journal of Structure Research and Practice
Journal Title(Ko) :한국교량및구조공학회 논문집
Volume : 3
No :1
Pages :1-8
Received Date : 2025-04-30
Accepted Date : 2025-05-14
DOI :https://doi.org/10.22725/JSRP.2025.3.1.1

Journal of Structure Research and Practice ISSN:3022-4241(Print) 3022-7267(Online) 한국교량및구조공학회 논문집

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