위상배열초음파탐상검사에 의한 보일러관 용접부의 결함 판별

Abstract

본 연구에서는 보일러관 용접부에 발생하는 주요 결함을 대상으로 ASME BPVC 제5장 4절에 근거하여 위상배열초음파탐상검사의 결함종류 판별과 결함크기 해상 특성을 확인하기 위해 방사선투과검사를 병행하여 수행하고 그 결과를 분석하였다. 이를 통해 위상배열초음파탐상검사는 용입부족, 융합불량 및 균열과 같은 면상결함군과 슬래그 및 기공과 같은 구상결함군의 결함종류 판별은 가능하였다. 그러나 각 군에서 형상이 유사한 결함의 종류를 판별하는 것은 용이하지 않음을 확인하였다. 결함의 크기가 합격, 불합격 여부에 영향을 미치는 슬래그는 방사선투과검사와 비교하여 결함의 위치나 방향에 무관하게 과소 예측되었고, 기공은 결함의 위치나 방향에 따라 과대 또는 과소 예측되는 특성을 보이므로 결함크기 판별에 주의를 요한다.|Coal-fired power plants have depended on radiography testing(RT) entirely for NDE of welding points in boiler tubes. But Nuclear safety law’s amendment caused many problems to use RT. Phased array ultrasonic testing(PAUT) is adapted instead of RT for NDE of welding points in boiler tubes these days. Unfortunately, PAUT doesn’t give us the discrimination characteristics about flaws distinction and flaws size clearly. In this thesis, analyse the distinction characteristic of flaws types and the detection characteristics of flaws size using PAUT for boiler tube welding points. This study’s conclusions are followings. First, PAUT can be used for NDE of welding points in boiler tubes because it can detect the flaws over depth 0.2 mm and length 0.5 mm. Second, PAUT can distinct between planar flaws and rounded flaws, but it is hard to tell apart the types of flaw respectively. Third, We pay attention to the discrimination of flaws size because PAUT tends to underestimate the flaw size of slag and underestimate or overestimate the flaw size of porosity.; Coal-fired power plants have depended on radiography testing(RT) entirely for NDE of welding points in boiler tubes. But Nuclear safety law’s amendment caused many problems to use RT. Phased array ultrasonic testing(PAUT) is adapted instead of RT for NDE of welding points in boiler tubes these days. Unfortunately, PAUT doesn’t give us the discrimination characteristics about flaws distinction and flaws size clearly. In this thesis, analyse the distinction characteristic of flaws types and the detection characteristics of flaws size using PAUT for boiler tube welding points. This study’s conclusions are followings. First, PAUT can be used for NDE of welding points in boiler tubes because it can detect the flaws over depth 0.2 mm and length 0.5 mm. Second, PAUT can distinct between planar flaws and rounded flaws, but it is hard to tell apart the types of flaw respectively. Third, We pay attention to the discrimination of flaws size because PAUT tends to underestimate the flaw size of slag and underestimate or overestimate the flaw size of porosity.