용접으로 인한 보강 및 비보강 원통관의 잔류응력과 변형 측정 실험연구

Abstract

용접으로 제작되는 구조물은 용접열에 의한 초기 형상결함과 잔류응력이 존재하게 된다. 초기 형상결함과 잔류응력응 정도의 차이는 있으나 대부분 구조물의 거동에 영향을 미치게 된다. 따라서 자수체의 최종강도를 정확히 추정하기 위하여는 용접으로 인한 잔류응력의 분포와 크기는 물론 변형의 경향을 ?컁피? 필요가 있다. 본 연구에서는 우선, 호칭경 300A 강과을 사용하였고, 보강 및 비보강 원통의 용접변형과 표면의 잔류응력만을 측정하여 그 결과를 해석하였다. 용접 입열량의 증가에 따라 변형과 잔류응력이 증가하였으며 축방향의 처짐변형은 심각하였다. 용접선 근처와 보강재가 위치한 곳에서 최대 잔류응력이 발생했으며 모재의 항복응력 보다 큰값으로 나타났다. 또한 축방향의 용섭선 길이가 증가 함에 따라 잔류응력 값도 증가됨을 볼 수 있었다.

The experimental study has been carried out in order to measure the magnitude of residual stresses(axial and circumferential) and deformation of cylindrical tube according to CO₂ welding. The effect of seam, butt joint and ring stiffening on the residualstresses and deformations was also investigated. The results of this study can be summarized as follows:

A. Deformation

1) In case of butt joint (stiffened and unstiffened tube) ;

Deformation rate of tube diameter increases progressively in accordance with heat input of welding. Maximum deflection is negligible in comparison with wall thickness. But in case of submerged body, such initial defects can cause serious problems.

2) In case of seam welding ;

Maximum deofrmation in was of the weld line is about 1.0mm as in butt joint. Circumferential deformation does not occure beyond 300mmdistance from the seam weld line. But the maximum deflection of weld line is 4.0mm, which may greatly reduce the axial strength.

B. Residual stresses

1) In case of seam weld;

·Residual stresses of axial and circumferential direction increase in accordance with the increment of seam weld length and is higher than the value of the yield stress of base metal in way of the weld line.

·Compressive and tensile components of residual stress diminish fluctuating like damped vibration from the weld line. The residual stress is vanished over 100mm off the weld line.

2) In case of butt weld (stiffened and unstiffened);

·residual stresses both in axial and hoop direction are higher than the yield stress of base metal at the weld line and stiffened position for tow cases.

·Axial load may cause stiffener buckling and radial pressure may cause inter-stiffener shell buckling.

The experimental study has been carried out in order to measure the magnitude of residual stresses(axial and circumferential) and deformation of cylindrical tube according to CO₂ welding. The effect of seam, butt joint and ring stiffening on the residualstresses and deformations was also investigated. The results of this study can be summarized as follows:

A. Deformation

1) In case of butt joint (stiffened and unstiffened tube) ;

Deformation rate of tube diameter increases progressively in accordance with heat input of welding. Maximum deflection is negligible in comparison with wall thickness. But in case of submerged body, such initial defects can cause serious problems.

2) In case of seam welding ;

Maximum deofrmation in was of the weld line is about 1.0mm as in butt joint. Circumferential deformation does not occure beyond 300mmdistance from the seam weld line. But the maximum deflection of weld line is 4.0mm, which may greatly reduce the axial strength.

B. Residual stresses

1) In case of seam weld;

·Residual stresses of axial and circumferential direction increase in accordance with the increment of seam weld length and is higher than the value of the yield stress of base metal in way of the weld line.

·Compressive and tensile components of residual stress diminish fluctuating like damped vibration from the weld line. The residual stress is vanished over 100mm off the weld line.

2) In case of butt weld (stiffened and unstiffened);

·residual stresses both in axial and hoop direction are higher than the yield stress of base metal at the weld line and stiffened position for tow cases.

·Axial load may cause stiffener buckling and radial pressure may cause inter-stiffener shell buckling.